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SYNOPSIS: Current Guidelines For M. tuberculosis Testing

U.S Department of Health and Human Services, Public Health Program, Centers for Disease Control, Public Health Program Office

Publication date: 01/01/1990

Table of Contents

Synopsis: Current guidelines for M. tuberculosis testing
The recommended rapid testing systems currently available are
Recommended managerial practices include
Table 1, Testing Practices


Testing Practices

Synopsis: Current guidelines for M. tuberculosis testing

The recommendations of the American Thoracic Society should be followed to determine if a laboratory should do mycobacterial testing. The recommendations are as follows:
  1. To maintain proficiency in acid-fast (AFB) microscopy, a minimum of 10 specimens per week should be examined.
  2. To maintain proficiency in culture and identification, 20 specimens per week should be digested and cultured.
The testing systems and managerial practices selected by a laboratory should be those that contribute to achieving a rapid turnaround time for isolating, identifying, and drug susceptibility testing M. tuberculosis. Using currently available systems, it is possible to achieve a turnaround time of 3 weeks from collection of the specimen to reporting results of susceptibility testing with primary drugs.

The recommended rapid testing systems currently available are

  • AFB Microscopy: Fluorochrome-staining
  • Isolation: Liquid media
Comment: Only the BACTEC radiometric system is available at this time. Other systems, however, are currently being evaluated and may be available shortly.


  • Genetic probe assays
  • HPLC (suitable for reference laboratories only)
Drug Susceptibility Testing: Primary drugs--streptomycin, isoniazid, rifampin, ethambutol, pyrazinamide--in liquid medium (BACTEC system).

Comment: No reliable system using liquid media is currently available for testing secondary drugs.

Recommended managerial practices include

  • Immediate testing of specimens and isolates; no daily holdovers for batching.
  • Immediate telephoning of significant results to clinicians/physicians at each stage of the testing process.
Laboratory Profile: A MODEL 20-200 Clinical Specimens per Week

Managerial Practices:

  • Determines that the laboratory receives a sufficient number of specimens or cultures to maintain proficiency in each test offered.
  • Maintains effective communication (via telephone and in writing) with clinicians in matters pertaining to specimen collection and transport.
  • Telephones clinicians immediately with test results; confirms with a written report.
  • Processes specimens immediately upon receipt.
  • Starts drug testing immediately upon identification of an isolate as M. tb. (does not hold for batching).
  • Provides partial to full laboratory coverage over weekends and holidays.
  • Knows when it is more prudent to send specimens and/or cultures to another laboratory for testing.
  • Works with other laboratories in the area for all to achieve the fastest turnaround time possible.

Table 1, Testing Practices

Table 1


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Table 1

                       Table 1. Testing Practices
Clinician                 Elapsed Time       Laboratory(a)
Collects specimen         0

Receives results of AFB   Day 1 to Day 2     -Receives specimen
microscopy                                   -Concentrates specimen
                                             -Evaluates fluorochrome-stained smear
                                             -Inoculates BACTEC culture medium(b)
                                             -(Inoculates drug(c) susceptibility medium w/AFB
                                               POSITIVE specimens)(d)

                           Day 2 to Day 10  -Incubates and monitors cultures

Receives culture and ID    Day 11 to Day 21 -Detects growth in culture medium
test results on positive                    -Test growth w/probes
specimens                                   -Inoculates BACTEC drug susceptibility medium

Receives drug              Day 15 to Day 28 -Obtains drug susceptibility results
susceptibility results
(a) Events in each frame occur within a 24 hour period.
(b) Solid media is also inoculated as backup
(c) Primary Drugs = streptomycin; isoniazid (INH); rifampin; ethambutol;
    pyrazinamide (PZA)
    Secondary Drugs = ethionamide; kanamycin; capreomycin; D-cycloserine;
    rifabutin; ciprofloxacin; amikacin
(d) Theoretically, direct drug testing ideal; realistically, dependibility
    of results variable

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