Scientific Data DocumentationInternational Classification Of Diseases - 9 (1975)ABSTRACTA classification of diseases may be defined as a system of categories to which morbid entities are assigned according to some established criteria. There are many possible choices for these criteria. The anatomist, for example, may desire a classification based on the part of the body affected whereas the pathologist is primarily interested in the nature of the disease process, the public health practitioner in aetiology and the clinician in the particular manifestation requiring his care. In other words there are many axes of classification and the particular axis selected will be determined by the interest of the investigator. A statistical classification of disease and injury will depend, therefore, upon the use to be made of the statistics to be compiled. Because of this conflict of interests, efforts to base a statistical classification a strictly logical adherence to any one axis have failed in the past. The various titles will represent a series of necessary compromises between classifications based on aetiology, anatomical site, circumstances of onset, etc., as well as the quality of information available on medical reports. Adjustments must also be made to meet the varied requirements of vital statistics offices, hospitals of different types, medical services of the armed forces, social insurance organizations, sickness surveys, and numerous other agencies. While no single classification will fit all the specialized needs, it should provide a common basis of classification for general statistical use; that is storage, retrieval and tabulation of data. A statistical classification of disease must be confined to a limited number of categories which will encompass the entire range of morbid conditions. The categories should be chosen so that they will facilitate the statistical study of disease phenomena. A specific disease entity should have a separate title in the classification only when its separation is warranted because the frequency of its occurrence, or its importance as a morbid condition, justifies its isolation as a separate category. On the other hand, many titles in the classification will refer to groups of separate but usually related morbid conditions. Every disease or morbid condition, however, must have a definite and appropriate place as an inclusion in one of the categories of the statistical classification. A few items of the statistical list will be residual titles for other and miscellaneous conditions which cannot be classified under the more specific titles. These miscellaneous categories should be kept to a minimum. It is this element of grouping in a statistical classification that distinguishes it from a nomenclature, a list or catalogue of approved names for morbid conditions, which must be extensive in order to accommodate all pathological conditions. The concepts of classification and nomenclature are, nevertheless, closely relate din the sense that some classifications (e.g. in zoology) are so detailed that they become nomenclatures. Such classifications, however, are generally unsuitable for statistical analysis. The aims of a statistical classification of disease cannot be better summarized than in the following paragraphs written by William Farr (1) a century ago: "The causes of death were tabulated in the early Bills of Mortality (Tables mortuaires) alphabetically; and this course has the advantage of not raising nay of those nice questions in which it is vain to expect physicians and statisticians to agree unanimously. But statistics is eminently a science of classification; and it is evident, on glancing at the subject cursorily, that any classification that brings together in groups diseases that have considerable affinity, or that are liable to be confounded with each other, is likely to facilitate the deduction of general principles. "Classification is a method of generalization. Several classifications may therefore, be used with advantage; and the physician, the pathologist, or the jurist, each from his own point of view, may legitimately classify the diseases and the causes of death in the way that he thinks best adapted to facilitate his inquiries, and to yield general results. "The medical practitioner may found his main divisions of diseases on their treatment as medical or surgical; the pathologist, on the nature of the morbid action or product; the anatomist or the physiologist on the tissues and organs involved; the medical jurist on the suddenness or the slowness of the death; and all these points well deserve attention in a statistical classification. "In the eyes of national statists the most important elements are, however, brought into account in the ancient subdivision of diseases into plagues, or epidemics and endemics, into diseases of common occurrence (sporadic diseases), which may be conveniently divided into three classes, and into injuries, the immediate results of violence or of external causes."BACKGROUNDEarly HistoryFrancois Bossier de Lacroix (1706-1777), better known as Sauvages, first attempted to classify diseases systematically. Sauvages' comprehensive treatise was published under the title Nosologia Methodica. A contemporary of Sauvages was the great methodologist Linnaeus (1707-1778), one of whose treatises was entitled Genera Morborum. At the beginning of the 19th century,t he classification of disease in most general use was one by William Cullen (1710-1790), of Edinburgh, which was published in 1785 under the title Synopsis Nosologiae Methodicae. The statistical study of disease, however, began for all practical purposes with the work of John Graunt on the London Bills of Mortality a century earlier. In an attempt to estimate the proportion of liveborn children who died before reaching the age of six years, no records of age at death being available, he took all deaths classed as thrush, convulsions, rickets, teeth and worms, abortives, chrysomes, infants, livergrown, and overlaid and added to them half the deaths classed as smallpox, swine pox, measles, and worms without convulsions. Despite the crudity of this classification his estimate of a 36 per cent mortality before the age of six years appears from later evidence to have been a good one. While three centuries have contributed something to the scientific accuracy of disease classification, there are many who doubt the usefulness of attempts to compile statistics of disease, or even causes of death, because of the difficulties of classification. To these, one can quote Major Greenwood (2): "The Scientific purist, who will wait for medical statistics until they are nosologically exact, is no wiser than Horace's rustic waiting for the rive to flow away". Fortunately for the progress of preventive medicine, the General Register Office of England and Wales, at its inception in 1837, found in William Farr (1807-1883)-its first medical statistician-a man who not only made the best possible use of the imperfect classifications of disease available at the time, but laboured to secure better classification and international uniformity in their use. Farr found the classification of Cullen in use in the public services of his day. It had not been revised so as to embody the advances of medical science, nor was it deemed by him to be satisfactory for statistical purposes. In the first Annual Report of the registrar General, therefore, he discussed the principles that should govern a statistical classification of disease and urged the adoption of a uniform classification. Both nomenclature and statistical classification received constant study and consideration by Farr in his annual "Letters" to the Registrar General published in the Annual Reports of the Registrar General. The utility of a uniform classification of causes of death was so strongly recognized at the first International Statistical Congress, held at Brussels, in 1853, that it requested William Farr and Marc d'Espine, of Geneva, to prepare "une nonmenclature uniforme des causes deces applicable a tous les pays". (3) At the next Congress, at Paris in 1855, Farr and d'Espine submitted two separate lists which were based on very different principles. Farr's classification was arranged under five groups: Epidemic diseases, Constitutional (general) diseases, Local diseases arranged according to anatomical site, Developmental diseases, and diseases that are the direct result of violence. D'Espine classified diseases according to their nature (gouty, herpetic, haematic, etc.). The Congress adopted a compromise list of 138 rubrics. In 1864, this classification was revised at Paris "sur le modele de celle de W. Farr", and was subsequently revised in 1874, 1880, and 1886. Although there was never any universal acceptance of this classification, the general arrangement, including the principle of classifying diseases by anatomical site, proposed by Farr has survived as the basis of the Internal List of Causes of Death.Adoption of International List of Causes of DeathThe International Statistical Institute, the successor to the International Statistical Congress, at its meeting in Vienna in 1891, charged a committee, of which Jacques Bertillon (1851-1922), Chef des Travaux statistiques de la ville de Paris, was chairman, with the preparation of a classification of causes of death. It is of interest to note that Bertillon was the grandson of Achille Guillard, a noted botanist and statistician, who had introduced the resolution requesting Farr and d'Espine to prepare a uniform classification at the First Statistical Congress in 1853. The report of this committee was presented by Bertillon at the meeting of the International Statistical Institute at Chicago in 1893 and adopted by it. The classification prepared by Bertillon was based on the classification of causes of death used by the City of Paris, which, since its revision in 1885, represented a synthesis of English, German, and Swiss classifications. The classification was based on the principle, adopted by Farr, of distinguishing between general diseases and those localized to a particular organ or anatomical site. In accordance with the instructions of the Vienna Congress made at the suggestion of L. Guillaume, the Director of the Federal Bureau of Statistics of Switzerland, Bertillon included three classifications: the first, an abridged classification of 44 titles; the second, a classification of 99 titles; and the third a classification of 161 titles. The Bertillon Classification of Causes of Death, as it was at first called, received general approval and was adopted by several countries, as well as by many cities. The classification was first used in North America by Jesus E. Monjaras for the statistics of San Luis de Potosi, Mexico. (4) In 1898, the American Public Health Association, at its meeting in Ottawa, Canada, recommended the adoption of the Bertillon Classification by registrars of Canada, Mexico, and the United States. The Association further suggested that the classification be revised every ten years. The meeting of the International Statistical Institute at Christiania in 1899, Bertillon presented a report on the progress of the classification, including the recommendations of the American Public Health Association for decennial revisions. The International Statistical Institute then adopted the following resolution: "The International Statistical Institute, convinced of the necessity of using in the different countries comparable nomenclatures: "Learns with pleasure of the adoption by all the statistical offices of North America, by some of those of South America, and by some in Europe, of the system of cause of death nomenclature presented in 1893: "Insists vigorously that this system of nomenclature be adopted in principle and without revision, by all the statistical institutions of Europe; "Approves, at least in its general lines, the system of decennial revision proposed by the American Public Health Association at its Ottawa session (1898); "Urges the statistical offices who have not yet adhered, to do so without delay, and to contribute to the comparability of the cause of the death nonmenclature." (5) The French Government therefore convoked at Paris, in August 1900, the first International Conference for the revision of the Bertillon or International Classification of Causes of Death. Delegates from 26 countries attended this Conference. A detailed classification of causes of death consisting of 179 groups and an abridged classification of 35 groups were adopted on 21 August 1900. The desirability of decennial revisions was recognized, and the French Government was requested to call the next meeting in 1910. Actually the next conference was held in 1909, and the Government of France called succeeding conference inn 1920, 1929, and 1938. Bertillon continued as the guiding force in the promotion of the International List of Causes of Death, and the revisions of 1900, 1910, and 1920 were carried out under his leadership. As Secretary-General of the International Conference, he sent out the provisional revision for 1920 to more than 500 persons, asking for comments. His death in 1922 left the International Conference without a guiding hand. At the 1923 session of the International Statistical Institute, Michel Huber, Bertillon's successor in France, recognized this lack of leadership and introduced a resolution for the International Statistical Institute to renew its stand of 1893 in regard to the International Classification of Causes of Death and to co-operate with other international organizations in preparation for subsequent revisions. The Health Organization of the League of nations had also taken an active interest in vital statistics and appointed a Commission of Statistical Experts to study the classification of diseases and causes of death, as well as other problems in the field of medical statistics. E. Roesle, Chief of the Medical Statistical Service of the German Health Bureau and a member of the Commission of Expert Statisticians, prepared a monograph that listed the expansion in the rubrics of the 1920 International List of Causes of Death that would be required if the classification was to be used in the tabulation of statistics or morbidity. This careful study was published by the Health Organization of the League of Nations in 1928. (6) In order to co-ordinate the work of both agencies, an international commission, known as the "Mixed Commission", was created with an equal number of representatives from the International Statistical Institute and the Health Organization of the League of Nations. This Commission drafted the proposals for the Fourth (1929) and the Fifth (1938) revisions of the International List of Causes of Death. The Sixth, Seventh, and Eighth Revisions The International Health Conference held in New York City in 1946 entrusted the Interim Commission of the World Health Organization with the responsibility of undertaking preparatory work for the next decennial revision of the International Lists of Causes of Death and for the establishment of International Lists of Causes of Morbidity (7). The International Conference for the Sixth Revision of the International Lists of Diseases and Causes of Death was convened in Paris in April 1949 by the Government of France and its secretariat was entrusted jointly to the competent French administrations and to the World Health Organization which had carried out the preparatory work under the Arrangement concluded by the governments represented at the International Health Conference in 1946 (7). The Sixth Decennial Revision Conference marked the beginning of a new era in international vital and health statistics. Apart from approving a comprehensive list for both mortality and morbidity and agreeing on international rules for selecting the underlying cause of death it recommended the adoption of a comprehensive programme of international co-operation in the field of vital and health statistics, including the establishment of national committee on vital and health statistics for the purpose of co-ordinating statistical activities in the country and to serve as a link between the national statistical institutions and the World Health Organization (8). The International Conference for the Seventh Revision of the International Classification of Diseases was held in Paris under WHO auspices in February 1955 (9). In accordance with a recommendation of the WHO Expert Committee on Health Statistics (10) this revision was limited to essential changes and amendments of errors and inconsistencies. The Eighth Revision Conference convened by WHO met in the Palais des Nations, Geneva, from 6 to 12 July 1965 (11). This revision was of more radical nature than the Seventh but left unchanged the basic structure of the Classification and the general philosophy of classifying diseases according to their aetiology rather than a particular manifestation.REPORT OF THE INTERNATIONAL CONFERENCE FOR THE NINTH REVISIONGeneral InformationThe International Conference for the Ninth Revision of the International Classification of Diseases convened by the World Health Organization met at WHO headquarters in Geneva from 30 September to 6 October 1975. The Conference was attended by delegations from 46 Member States: Algeria Nigeria Australia Norway Austria Poland Belgium Portugal Brazil Saudi Arabia Canada Singapore Chad Spain Denmark Sudan Egypt Sweden Finland Switzerland France Thailand German Democratic Republic Togo Germany, Federal Republic of Trinidad and Tobago Guatemala Tunisia Hungary Union of Soviet Socialist Republics India United Arab Emirates Indonesia United Kingdom of Great Britain Ireland and Northern Ireland Israel United Republic of Cameroon Italy United States of America Japan Venezuela Libyan Arab Republic Yugoslavia Luxembourg Zaire Netherlands, Kingdom of the The United Nations, the Organization for Economic Cooperation and Development, the International Labour Organization and the International Agency for Research on Cancer sent representatives to participate in the Conference, as did the Council for International Organizations of Medical Sciences and ten other international non- governmental organizations concerned with dental health, dermatology, gynaecology and obstetrics, mental health, dermatology, gynaecology and obstetrics, mental health, neurosurgery, ophthalmology, paediatrics, pathology, radiology, and rehabilitation of the disabled. The Conference was opened by Dr. A. S. Pavlov, Assistant Director-General, on behalf of the Director-General. Dr. Pavlov reviewed the history of the ICD, reminding delegates that it had developed from an International List of Causes of Death, first agreed in 1893. WHO took over responsibility with the Sixth Revision and its concern with the ICD is written into its Constitution. Since WHO took over, there had been a great extension of use of the ICD for the indexing and retrieval of records and for statistics concerning the planning, monitoring and evaluation of health services, besides its traditional use in epidemiology. The Conference elected the following officers: Chairman: Dr. R. H. C. Wells (Australia) Vice-Chairmen: Dr. J. M. Avilan-Rovira (Venezuela) Dr. G. Cerkovnij (USSR) Dr. I. M. Moriyama (United States of America) Mr. G. Paine (United Kingdom) Rapporteurs: Dr. M. S. Heasman (United Kingdom) Dr. (Mlle) M. Guidevaux (France) Secretariat: Dr. A. S. Pavlov (Assistant Director-General, WHO) Mr. K. Uemura (Director, Division of Health Statistics, WHO) Dr. K. Kupka (Chief Medical Officer, International Classification of Disease, WHO) (Secretary) Mr. H. G. Corbett (Statistician, International Classification of Diseases, WHO) Professor G. G. Avtandilov (USSR) (Temporary Adviser) The Conference adopted an agenda dealing with the Ninth Revision of the International Classification of Diseases, with several provisional supplementary classifications intended for use in conjunction with it, and with allied topics. Ninth Revision of the International Classification of DiseasesReview of activities in the preparation of the proposals for the Ninth Revision The procedures leading up to the Ninth Revision commenced in 1969 with the calling of a Study Group. The work had been planned and carried out so that the proposals before the Conference were in a much more advanced state of preparation than had been the case at earlier revisions. The intention was to have the completed manual, with its alphabetical index, in the hands of users in good time to allow for adequate training and familiarization in countries before its introduction. The progress of preparations for revision had been guided by further meetings of the Study Group and by meetings of Heads of Centres for Classification of Diseases. The first meeting of the Study Group considered that the revision ought to be a limited one. It soon became clear, however, that a much more radical revision was being demanded by specialists in many fields of medicine. Views were sought from individual consultants, international specialists bodies, the WHO Centres for Classification of Diseases and headquarters units. Regional offices arranged meetings so that representatives of Member States could give their views. The third meeting of the Study Group considered proposals incorporating views from all these sources, and on the basis of their recommendations draft proposals were circulated to Member States in mid-1973. Comments on the proposals were considered by the WHO Expert Committee on Health Statistics in June 1974 (12), and the proposals before the Conference were the results of its recommendations. Delegates from several countries spoke in support of the revision as proposed. In particular it was reiterated that clinical pressures had demanded an extensive revision at this stage on the grounds that he structure of several of the ICD chapters was out of touch with modern clinical concepts. The delegation from sweden, on behalf of the five Nordic countries (Denmark, Finland, Iceland, Norway and Sweden), put forward the view that the problems and cost associated with so extensive a change would be substantial since these countries had established a 5-digit version based on the ICD-8 which was widely used in computerized health information systems. They considered that this 5-digit version met to a large extent the clinical demands for greater specificity which the Ninth Revision was aiming at. The Conference noted the concern of the Nordic countries but, recognizing the need pointed out by several countries to satisfy clinical requirements by structural changes as well as by providing increased specificity, in general supported the scope of the proposed revision as presented to the Conference. History and Development of Uses of the ICD The Conference was reminded of the impressive history of the classification. Its origins lay in a list of causes of death, which was used for many years. At the Sixth Revision, the classification was extended to cover non-fatal conditions. Later the classification had been shown to be useful for the purposes of hospital indexing, particularly if adapted by means of some extra subdivision. More recently adaptations had been made for use in medical audit systems. The Ninth Revision proposals include a device designed to improve its suitability for use in statistics for the evaluation of medical care. For the future, it would have to be decided what kind of adaptation of the ICD would render it usable for Health Insurance Statistics, and whether it was possible to adapt it as a basis for central payment for medical services. All these uses tended to push the classification in the direction of more detail. At the other end of the scale it had to be remembered that there were demands from countries and areas where such sophistication was irrelevant but which nevertheless would like a classification based on the ICD so as to assess their progress in health care and in the control of sickness. General Characteristics of the Proposed Ninth Revision The general arrangement of the proposals for the ninth Revision considered by the Conference was much the same as in the eighth Revision, though with much additional detail. care had been taken to ensure that the categories were meaningful at the 3- digit level. There were certain innovations: (i) Optional fifth digits were provided in certain places: for example for the mode of diagnosis in tuberculosis, for method of delivery in chapter XI, for anatomical site in musculoskeletal disorders and for place of accident in the E code. (ii) An independent 4-digit coding system was provided to classify histological varieties of neoplasm, prefixed by the letter M (for morphology) and followed by a fifth digit indicating behavior. This code was for optional use in addition to the normal code indicating topography. (iii) The role of the E code for external causes had changed. In the Sixth, Seventh and Eighth Revisions, Chapter XVII consisted of two alternative classifications, one according to the nature of the injury (the N code) and one according to external cause (the E code). In the Ninth Revision it was proposed to drop the N prefix and consider only the nature of injury as part of the main classification. The E code becomes a supplementary classification to be used, where relevant in conjunction with codes form any part of the classification. For mortality statistics, however, the E code should still be used in preference to Chapter XVII in presenting underlying causes of death, when only one is used. (iv) The Ninth Revision proposals included dual classification of certain diagnostic statements. The Conference heard that the system had been introduced into the 1973 proposals after it had become obvious that there was a demand to classify diseases according to important manifestations, e.g. to classify numps encephalitis to a category for encephalitis. It would have been unwise to change the whole axis of the ICD to this basis, so the first proposal was to make the positioning according to manifestation alternative to the traditional placing according to aetiology. As a result of criticism, it is now proposed that the "traditional" aetiology codes, those marked with a+, should be considered primary, and the new codes, positioned in the classification according to manifestation and marked with an *, should be secondary, for use in applications concerned with the planning and evaluation of medical care. This system applies only to diagnostic statements that contain information about both etiology and manifestation and when the latter is important in its own right. (v) Categories in the Mental Disorders Chapter include descriptions of their content with a view to overcoming the particular difficulties in this field, where international terminology is not standard. The V code (formerly the Y code) continues to appear in Volume 1. These characteristics of the proposed revision were accepted by the Conference.Adoption of the Ninth Revision of the InternationalClassification of Diseases. The Conference, Having considered the proposals prepared by the Organization on the recommendations of the Expert Committee on Health Statistics (12), Recognizing the need for a few further minor modifications to meet the comments on points of detail submitted by Member States during the Conference, Recommends that the revised Detailed List of Categories and Sub-Categories in Annex I. to this report constitute the Ninth Revision of the International Classification of Diseases. Classification of Procedures in MedicineIn response to requests from a number of Member States, the Organization had drafted a classification of therapeutic, diagnostic and prophylactic procedures in medicine, covering surgery, radiology, laboratory and other procedures. Various national classifications of this kind had been studied and advice sough from hospital associations in a number of countries. The intention was to provide a tool for use in the analysis of health services provided to patients in hospitals, clinics, outpatient departments, etc. The Conference congratulates the Secretariat on this important development and Recommends that the provisional procedures classifications should be published as supplements to, and not as integral parts of the Ninth Revision of the International Classification of Diseases. They should be published in some inexpensive form and, after two or three years' experience, revised in the light of users' comments.Classification of Impairments and Handicaps The ICD provided the means of classifying current illness or injury; the classification of procedures provided a means of coding the treatment or other services consumed by the patient. There remained a need to classify impairments and the consequent handicaps or disadvantages. This was an area in which much development was occurring and a draft classification had been prepared by the Organization although this was to a large extent experimental and exploratory. It had been drafted after much consultation with agencies responsible for social services and rehabilitation. The Conference having considered the classification of Impairments and Handicaps believes that these have potential value and accordingly Recommends that the Impairments and Handicaps classifications be published for trial purposes as a supplement to, and not as an integral part of, the Ninth Revision of the International Classification of Diseases.Adaptations of ICD for the Use of Specialists The Conference noted three adaptations of the ICD which had been designed for the sue of specialists. The first was an adaptation for oncology-ICD-O. Coding was on three axes indicating the topography, morphology and behaviour of tumours. The 4-digit topography code was based on the list of sites of the malignant neoplasm section of Chapter II of the Ninth Revision of the ICD, but was to be used for any type of neoplasm. To this would be added a 4-digit code indicating histological variety of neoplasm, and a single-digit code indicating behaviour. It was intended that the code should be used by centres requiring to record extra detail about tumours, as an alternative to the Ninth Revision of ICD, with which it was entirely compatible. (A conversion guide would be available, enabling translation of codes by computer if desired.) Other adaptations had been produced for dentistry and stomatology and for ophthalmology. Each of these contains, a small volume, all conditions of interest to the specialist, selected from all chapters of the ICD, and provides additional detail by means of a fifth digit.Lay Reporting The Conference discussed the problem of securing badly needed morbidity and mortality statistics in countries still suffering from a lack of sufficiently qualified personnel. There was a divergence of opinion concerning the system of classification to be used where information about sickness or causes of death is necessarily furnished by persons other than physicians. Some delegates considered that the International Classification of Diseases in some simplified form (e.g. one of the tabulation lists) would serve this purpose while others believed that a system independent of the ICD needed to be established. A small working party, consisting of delegates from Member States with experience of the problem, was convened to consider the question in more detail and in the light of its reportThe Conference, Realizing the present problem involved in the full utilization of ICD by the developing countries in most of the regions; Recognizing the need for introducing a system which could provide useful and objective morbidity and mortality data for efficient health planning; Appreciating the field trials conducted in some countries for collection of morbidity and mortality information through non- medical health or other personnel and the experience thus obtained; Noting the concern of the World Health Organization for development and promotion of health services, particularly in the developing countries, as contained in resolutions EB55.R16 (13), WHA28.78 (14), WHA28.77 (15) and WHA28.88 (16), Recommends that the World Health Organization should (1) become increasingly involved in the attempts made by the various developing countries for collection of morbidity and mortality statistics through lay or paramedical personnel; (2) organize meetings at regional level for facilitating exchange of experiences between the countries currently facing this problem so as to design suitable classification lists with due consideration to national differences in terminology; (3) assist countries in their endeavor to establish or expand the system of collection or morbidity and mortality data through lay or paramedical personnel.Statistics of Death in the Perinatal Period and Related Matters The conference considered with interest the reports of the Scientific Group on Health Statistics Methodology relating to Perinatal Events (17) and the recommendations of the Expert Committee (12) on this subject. These were the culmination of a series of special WHO meetings attended by specialists from many disciplines. It had become clear that a review of the situation was needed in the light of certain developments in medical sciences, notably those leading to the improved survival of infants born at a very early gestational age. After discussion, the Conference Recommends that, where practicable, statistics in relation to perinatal deaths should be derived from a special certificate of perinatal death (instead of the normal death certificate) and presented in the manner set out in Annex II, which also includes relevant definitions. This annex also includes recommendations in respect of maternal mortality statistics.Mortality Coding Rules The Conference was made aware of the problems arising in selecting the underlying cause of death where this was the result of factors connected with surgical or other treatment. It was proposed that where ann untoward effect of treatment is responsible for death then this should be coded rather than the condition for which the treatment was given. Although there were views expressed by some delegates that this interfered with the traditional underlying cause concept, the Conference preferred the former view and accordingly Recommends that the modification rule in Annex III be added to the existing rules for selection of cause of death for primary mortality tabulation. The Conference was also informed that additional guidelines for dealing with certificates of death from cancer had been drafted and were being tested in several countries. If the tests showed that the guidelines improved consistency in coding, they would be incorporated into the Ninth Revision.Selection of a Single Cause for Statistics or Morbidity No rules had hitherto been incorporated into the ICD concerning the tabulation of morbidity. Routine statistics are normally based upon a single cause and the Conference considered that the application of the ICD to routine morbidity statistics had reached a point where international recommendations for selection of single cause for presentation of morbidity statistics was appropriate and accordingly Recommends that the condition to be selected for single-cause analysis for health-care records should be the main condition treated or investigated during the relevant episode of hospital or other care. If no diagnosis was made, the main symptom or problem should be selected instead. Whenever possible, the choice should be exercised by the responsible medical practitioner or other health-care professional and the main condition or problem distinguished from other conditions or problems. Short Lists for Tabulation of Mortality and Morbidity Difficulties had become apparent in the use of the present short lists A, B, C and D for the tabulation of mortality and morbidity. Their construction and numbering was such that confusion often arose and comparability of statistics based on different lists presented some difficulties. Proposed new lists were presented to the Conference in which totals were shown for groups of diseases and for certain selected individual conditions. Minimum lists of 55 items were recommended for the tabulation of mortality and morbidity and countries could add to these further items from a basic list of 275 categories. The Conference Recommends that the Special Tabulation Lists set out in Annex IV to this report should replace the lists for tabulation of morbidity and mortality and should be published as part of the International Classification of Diseases together with appropriate explanation and instruction as to their use.Multiple Condition Coding and Analysis The Conference noted with interest the extended use of multiple condition coding and analysis in a number of countries with a variety of ends in view. One example was the study of the interrelationship of various conditions recorded on a death certificate; another was to permit computer selection of the underlying cause of death. The Conference also noted the value of a store of multiple-coded national data on mortality and morbidity. The Conference expressed encouragement of such work but did not recommend that the ICD should contain any particular rules or methods of analysis to be followed.Different Disease-Coding Systems The Conference was reminded of the existence of other disease classifications and reviewed their attributes as a preliminary to discussion of the possible form of the Tenth Revision. Some of these classifications are developments from the International Classification of Diseases; other are multi-axial, enabling retrieval from different viewpoints but not primarily designed with the presentation of routine statistics in mind. In others, a unique code is given to each disease or term, enabling retrieval of specific conditions and assembly into alternative classifications according to need. These developments seemed to indicate some desire for greater flexibility and to raise doubts as to whether a single multi-purpose classification was any longer practicable. It was felt that multi-axial classification often destroyed the ability to retrieve disease terms. Allocating a unique code to a disease or term might be one way of over-coming problems caused by changes in classification.Tenth Revision of the International Classification of Diseases The Conference recognized the need to make an early start in planning the next revision of the classification and discussed a number of questions that needed to be settled before detailed work could begin. The most fundamental point was that the Organization's programme was no longer confined to disease classification alone. Many other reasons, social and economic, for contact with health services were now included in the main classification and supplementary classifications of procedures in medicine and impairments and handicaps had been added. These needed to be further developed and incorporated into a comprehensive and coordinated system of classifications of health information. The name of the Organization's programme should reflect the wider scope of its activities. Standardization of nomenclature on a multilingual basis was essential for conformity in diagnosis, and glossaries similar to the one developed for psychiatry might be provided for other specialties where diagnostic concepts were unclear. A lack of balance in the Eight Revision, which contained 140 categories for infectious diseases but only 20 for the whole of perinatal morbidity, had been retained in the Ninth Revision because of its essentially conservative nature, but such a restriction should not necessarily hold for the next revision. It was acknowledged that conflicts existed between the need for a fairly broad classification for the purpose of international comparisons and the desire for a very high degree of specificity for diagnostic indexing and for epidemiological research, and between the requirements of a classification usable at the community level in developing countries and one suitable for a national morbidity programme with access to a computer. The structure of the Tenth Revision was another question for urgent decision; should the present uni-axial system be retained or should there be a move to a multi-dimensional approach; should the coding and classification elements be separated so that the former could remain constant while the latter could be revised at shorter intervals than at present? The view of the Conference was that these questions should be decided within the next two or three years by the construction and trial of model classifications of various types. It was recognized that this would be an additional task to the normal work of the Organization in this area and would require the provision of extra resources. The Conference recognized the great value of the work already done and still being done on ICD; it also recognized the rapidly increasing demands for more flexibility than is available in the present structure of this classification. The Conference, Noting that the ICD, despite the present constraints upon resources, which it completely absorbs, is one of the most influential activities of WHO, Recommends that: (1) WHO should continue its work in developing revisions of the ICD and related classifications and that the Organization's activity in connexion with the revision of the ICD should be expanded; (2) the ICD programme should be given sufficient resources to enable it simultaneously to explore the needs for new departures in the realm of health classifications and how these can be met without detracting from the present revision process; the programme should also be enabled to carry out extensive field trials of the various alternative approaches that exist or which may emerge. The Conference expressed the hope that efforts would be made to retain the continuity of expertise that had been developed in the Organization, in the centres for classification of diseases and among numerous organizations and individuals throughout the world.Publication of the Ninth Revision The Conference was informed that although the Tabular List of the ICD (Volume 1) in English and French could be made available in published form by the end of 1976, it was unlikely that the alphabetical Index (Volume 2) could be published before the middle of 1977. The Russian and Spanish versions should follow the English and French fairly closely. Member States intending to publish national language versions would receive pre-publication copies of the various parts of the classification as and when they were completed by the Secretariat to enable them to adhere as nearly as possible to this timetable. Several delegates pointed out that the late appearance off the alphabetical indexes at the Eight Revision had resulted in a high rate of coding errors during the first year of use. Because of the large amount of work still to be done before the Ninth Revision can be published and because the training of coders requires that both volumes, including the alphabetical index, should be inn the hands of users some 12 months before it is due to come into use, The Conference Recommends that the Ninth Revision of the International Classification of Diseases should come into effect on 1 January 1979. Familiarization and Training in the Use of the Ninth Revision There were many aspects of the proposed revision, besides the change in the categories themselves, which would require very careful explanation to coders and to users of statistics based on the ICD. It was planned that familiarization courses would be organized by the WHO regional offices, to help Member countries in planning their own courses. The Conference noted with interest that WHO hoped to prepare a set of training material covering an instructional course for coders of approximately two weeks, to make sure that the instruction was as consistent as possible. WHO would also make available explanatory material for users of statistics.ADOPTION OF THE NINTH REVISION The Twenty-ninth World Health Assembly, meeting in Geneva in May 1976, adopted the following resolution with regard to the Manual of the International Classification of Diseases (Resolution WHA29.34) (18). The Twenty-ninth World Health Assembly, Having considered the report of the International Conference for the Ninth Revision of the International Classification of Diseases, 1. Adopts the detailed list of three-digit categories and optional four digit sub-categories recommended by the Conference as the Ninth Revision of the International Classification of Disease, to come into effects as from 1 January 1979; 2. Adopts the rules recommended by the Conference for the selection of a single cause in morbidity statistics; 3. Adopts the recommendations of the Conference regarding statistics of perinatal and maternal mortality, including a special certificate of cause of perinatal death for use where practicable; 4. Requests the Director-General to issue a new edition of the Manual of the International Classification of Disease (Resolution WHA29.35) (19). The Twenty-ninth World Health Assembly. Noting the recommendations of the International Conference for the Ninth Revision of the International Classification of Diseases in respect of activities related to the Classification, 1. Approves the publication, for trial purposes, of supplementary classifications of Impairments and Handicaps and of Procedures in Medicine as supplements to, but not as integral parts of, the International Classification of Diseases; 2. Endorses the recommendation of the Conference concerning assistance to developing countries in their endeavor to establish or expand the system of collection of morbidity and mortality statistics through lay or paramedical personnel; 3. Endorses the request made by the Executive Board in resolution EB57.R34 (20) to the Director-General that he investigate the possibility of preparing an International Nonmenclature of Diseases as an improvement to the Tenth Revision of the International Classification of Diseases.MANUAL OF THE NINTH REVISIONConventions Used in the Tabular List The Tabular List makes special use of parentheses and colons which needs to be clearly understood. When parentheses are used for their normal function of enclosing synonyms, alternative wordings or explanatory phrases, square brackets +...+ are employed. Round brackets (...) are used to enclose supplementary words which may be either present or absent in the statement of a diagnosis without affecting the code number to which it is assigned. Words followed by a colon +:+ are not complete terms, but must have one or other of the understated modifiers to make them assignable to the given category. "NOS" is an abbreviation for "not otherwise specified" and is virtually the equivalent of "unspecified" and "unqualified". As an example of the use of the above conventions, category 464.0, Acute laryngitis, includes the following terms: Laryngitis (acute): NOS Haemophilus influenzae +H. influenzae+ oedematous pneumococcal septic suppurative ulcerative This signifies that to this category should be assigned laryngitis, with or without the adjective "acute", if standing alone or if accompanied by one or other of the modifiers: Haemophilus influenzae +of which H. influenzae is an alternative wording+, oedematous, pneumococcal, septic, suppurative, or ulcerative. Influenzal, streptococcal, diphtheritic, tuberculous, and chronic laryngitis will be found in other categories.Dual Classification of Certain Diagnostic Statements The Ninth Revision of the ICD contains an innovation that there are two codes for certain diagnostic descriptions which contain elements of information both about a localised manifestation or complications and about a more generalised underlying disease process. One of the codes-marked with a dagger (+) - is positioned in the part of the classification in which the diagnostic description is located according to normal ICD principles, that relating to the underlying disease, and the other - marked with an asterisk (*) - is positioned in the chapter of the classification relating to the organ system to which the manifestation of complication relates. Thus tuberculous meningitis has its dagger code in the chapter for infectious and parasitic diseases, and its asterisk code in the nervous system chapter. The necessity for this arose from the desire of specialists and those concerned with statistics of medical care to have certain manifestations which are medical-care problems in their own right classified in the chapters relating to the relevant organ system. The ICD has traditionally classified generalised diseases and infectious disease entities which may affect several parts of the body to special chapters of the classification, and their manifestations are normally assigned to the same place, so that until now tuberculous meningitis has been classifiable only to the infectious and parasitic diseases chapter. The dagger and asterisk categories are in fact alternative positionings in the classification for the relevant conditions, enabling retrieval or statistical analysis from either viewpoint. It is, however, a principle of ICD classification that the dagger category is the primary code and that the asterisk code is secondary, so it is important where it is desired to work with the asterisk code, and both are used, to use some special mark or a predetermined positioning in the coded record, to identify which is the dagger, and which the asterisk, code for the same entity. The criteria adopted in the Ninth Revision are that asterisk categories are provided: (i) if the manifestation or complication represents a medical-care problem in its own right and is normally treated by a specialty different from the one which would handle the underlying condition, and (ii) if the information about both the manifestation and the underlying condition is customarily contained in one diagnostic phrase (such as "diabetic retinitis"), or (iii) if the category relating to the manifestation is subdivided according to the cause-an example is arthropathy in which the subdivisions relate to broad groups of causes. Other underlying condition/manifestation combinations exist which do not cause coding and retrieval problems and have therefore not been incorporated in the "dagger and asterisk" system. Examples are: (i) situations where the two elements are customarily recorded as discrete diagnostic phrases and can be dealt with simply by coding the two terms separately, e.g. certain types of anaemia which may be the consequence of other diseases; the classification of the anaemia is usually according to its morphological type and does not depend on the cause; (ii) where the manifestation is an intrinsic part of the basic disease and is not regarded as a separate medical-care problem; for example, cholera, dysentery, etc. in the infectious and parasitic diseases chapter do not have asterisk categories in the digestive system chapter; lower genito-urinary tract manifestations of venereal diseases, in the infectious and parasitic diseases chapter, do not have asterisk categories in the genito-urinary diseases chapter, although gonococcal salpingitis and orchitis do; (iii) where the ICD has traditionally classified the condition according to the manifestation, e.g. anaemia due to enzyme defect. The areas of the Classification where the dagger and asterisk system operates are limited; there are about 150 rubrics of each in which asterisk-or dagger-marked terms occur. They may take one of three different forms:- (i) if the symbol (+ or *) and the alternative code both appear in the title of the rubric, all terms classifiable to that rubric are subject to dual classification and all have the same alternative code, e.g. 049.0+ Lymphocytic choriomeningitis (321.6*) Lymphocytic: meningitis (serous) meningoencephalitis (serous) 321.2* Meningitis due to ECHO virus (047.1+) Meningo-eruptive syndrome (ii) if the symbol appears in the title but the alternative code does not, all terms classifiable to that rubric are subject to dual classification but they have different alternative codes (which are listed for each term), e.g. 074.2+ Coxsackie carditis Aseptic myocarditis of Coxsackie: newborn (422.0*) endocarditis (421.1*) myocarditis (422.0*) pericarditis (420.0*) 420.0* Pericarditis in diseases classified elsewhere Pericarditis (acute): Pericarditis (acute): Coxsackie (074.2+) tuberculous (017.8+) meningococcal (036.4+) uraemic (585+) syphilitic (093.8+) (iii) if neither the symbol nor the alternative code appear in the title, the rubric as a whole is not subject to dual classification but individual inclusion terms may be; if so, there terms will be marked with the symbol and their alternative codes, e.g. 078.5 Cytomegalic inclusion disease Cytomegalic inclusion virus hepatitis+ (573.1*) Salivary gland virus disease 424.3 Pulmonary valve disorders Pulmonic regurgitation: NOS syphilitic* (093.2+) The use of asterisk coding is entirely optional. It should never be employed in coding the underlying cause of death (only dagger coding should be used for this purpose) but may be used in morbidity coding and in multiple-condition coding whether in morbidity or mortality. Any published tabulations, whether according to the detailed list or one of the short lists, of frequencies based on asterisk coding should be clearly annotated "Based on ICD asterisk coding".Role of the E Code As explained in the Report of the International Revision Conference (see paragraph 1.3 (iii), page XVI), the E Code is now a supplementary classification that may be used, if desired, to code external factors associated with morbid conditions classified to any part of the main classification. For single-cause tabulation of the underlying cause of death, however, the E Code should be used as the primary code if, and only if, the morbid condition is classifiable to Chapter XVII (Injury and Poisoning).Gaps in the Numbering System It will be noticed that certain code number have not been used, leaving gaps in the numbering system. The reason for this practice was to avoid unnecessary change sin code numbers familiar to coders who have been using the Eighth Revision) has been moved to category 785.4; in order to avoid changing the code numbers of categories 446 (Polyarteritis nodosa and allied conditions), 447 (Other disorders of arteries and arterioles) and 448 (Diseases of capillaries), it was preferred to leave the code number 445 unused in the Ninth Revision.Glossary of Mental Disorders A glossary describing and defining the content of rubrics in Chapter V (Mental Disorders) was published separately from the Eighth Revision of the International Classification of Diseases. in the Ninth Revision, the glossary has been incorporated into the Classification itself (see pages 177-213). The glossary descriptions are not intended as an aid for the lay coder, who should code whatever diagnostic statement appears on a medical record according to the provisions of the Tabular List and Alphabetical Index. Their purpose is to assist the person making the diagnosis, who should do so on the basis of the descriptions rather than the category titles, which may differ in meaning from place to place.ADAPTATIONS OF THE ICDDentistry and Stomatology The "Application of the ICD to Dentistry and Stomatology" (ICD-DA), based on the Eighth Revision of the ICD, was prepared by the Oral Health Unit of WHO and firs published in 1969. It brings together those ICD categories that include "diseases or conditions that occur in, have manifestations in, or have associations with the oral cavity and adjacent structures". It provides greater detail by means of a fifth digit, but the numbering system is so organized that the relationship between an ICD-DA code and the ICD code from which it is derived is immediately obvious and frequencies for ICD-DA categories can be readily aggregated into ICD categories. ICD-DA has been revised to concord with the Ninth Revision of the ICD and this revision was published by the World Health Organization in 1977. Oncology The "International Classification of Diseases for Oncology" (ICD-O) was published by the World Health Organization in 1976. Developed in collaboration with the International Agency for Research on Cancer (WHO) and the United States National Cancer Institute, with input from many other counties and extensive field trials, the ICD-O is intended for use in cancer registries, pathology departments and other agencies specializing in cancer. ICD-O is a dual-axis classification, providing coding systems for topography and morphology. The topography code uses for all neoplasms the same three- and four-digit categories that the Ninth Revision of ICD uses for malignant neoplasms (categories 140-199), thus providing increased specificity of site for other neoplasms, where the ICD provides a more restricted topographical classification or none at all. The morphology code is identical to the neoplasms section of the morphology field of the Systematized Nomenclature of Medicine (SNOMed) (21) and is compatible with the 1968 Edition of the Manual of Tumor Nomenclature and Coding (MOTNAC) (22) and the Systematized Nomenclature of Pathology (SNOP) (23). It is a five-digit code, the first four digits identifying the histological type and the fifth the behaviour of the neoplasm (malignant, in situ, benign, etc.). The ICD-O morphology code also appears in this Volume (see pages 667-690) and in the Alphabetical Index. In addition to the topography and morphology codes, ICD-O also includes a list of tumour-like lesions and conditions. A table explaining the method of converting ICD-O codes into ICD codes will be published in due course. Ophthalmology The International Council of Ophthalmology, supported by ophthalmological groups in many countries, has prepared a Classification of Disorders of the Eye, based on the Ninth Revision of the ICD. In addition to the ICD section "Disorders of the eye and adnexa" (categories 360-379), it includes all other ICD categories that classify eye disorders, from infectious diseases to injuries. It is a five-digit level but introducing additional detail at the fifth digit for the use of specialists. The classification was published in the "International Nomenclature of Ophthalmology" by the American Academy of Ophthalmology and Otolaryngology (24) in 1977, which also includes definitions or short descriptions of all terms, synonyms and equivalent terms in French, German and Spanish, and reference terms to facilitate literature retrieval.WHO CENTERS FOR CLASSIFICATION OF DISEASES Six WHO Centres have been established to assist countries with problems encountered in the classification of diseases and, in particular, in the use of the ICD. They are located in institutions in Paris (for French language users), Sao Paulo (for Portuguese), Moscow (for Russian) and Caracas (for Spanish); there are two Centres for English language users, in London and, for North America, in Washington, D.C., USA. Communications should be addressed as follows:- Head, WHO Centre for Classification of Diseases Office of Population Censuses and Surveys St. Catherine's House 10 Kingsway London WC2B 6JP United Kingdom or Head, WHO Center for Classification of Diseases for North America National Center for Health Statistics US Public Health Service Department of Health, Education and Welfare Washington, DC., United States of AmericaREFERENCES1. Registrar General of England and Wales, Sixteenth Annual Report, 1856, Appendix, 75-76 2. Greenwood, M. (1948) Medical statistics from Graunt to Farr. Cambridge, p. 28 3. Registrar General of England and Wales, Sixteenth Annual Report, 1856, Appendix, p. 73 4. Bertillon, J. (1912) Classification of the causes of death. (Abstract). Trans. 15th Int. Cong. Hyg. Demog., Washington, pp. 52-55 5. Bull. Inst. int. Statist. 1900, 12, 280 6. ROESLE, E. (1928) Essai d'une statistique comparative de la morbidite devant servir a etablir les listes speciales des causes de morbidite. Geneva (League of nations Health Organization, document C.H. 730) 7. Off. Rec. Wld Hlth Org., 1948, 2, 110 8. Off. Rec. Wld Hlth Org., 1948, 11, 23 9. World Health Organization (1955) Report of the International Conference for the Seventh Revision of the International Classification of Diseases, Geneva (unpublished document WHO/HS/8 Rev. Conf./17 Rev.1) 10. Wld Hlth Org. techn. Rep. Ser., 1952, 53 11. World Health Organization (1965) Report of the International Conference for the Eighth Revision of the International Classification of Diseases, Geneva (unpublished document WHO/HS/8 Rev. Conf./17 Rev.1 ) 12. World Health Organization, Expert Committee on Health Statistics (1974) Ninth Revision of the International Classification of Diseases, Geneva (unpublished document WHO/ICD9/74.4) 13. Off. Rec. Wld Hlth Org., 1975, 223, 10 14. Off. Rec. Wld Hlth Org., 1975, 227, 42 15. Off. Rec. Wld Hlth Org., 1975, 226, 44 16. Off. Rec. Wld Hlth Org., 1975, 226, 53 17. World Health Organization, Scientific Group on Health Statistics Methodology related to Perinatal Events (1974), Geneva (unpublished document ICD/PE/74.4) 18. Off. Rec. Wld Hlth Org., 1976, 233, 18 19. Off. Rec. Wld Hlth Org., 1976, 233, 18 20. Off. Rec. Wld Hlth Org., 1976, 231, 25 21. College of American Pathologists (1976), Systematized Nomenclature of Medicine, Chicago, Illinois 22. American Cancer Society, Inc. (1968), Manual of Tumor Nomenclature of Medicine, Chicago, Illinois 23. College of American Pathologists (1965), Systematized Nomenclature of Pathology, Chicago, Illinois 24. American Academy of Ophthalmology and Otolaryngology (1977), International Nomenclature of Ophthalmology, 15 Second Street, S.W., Rochester, Minnesota 55901.
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