U.S. flag

An official website of the United States government

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Systematic Screening for Active Tuberculosis: Principles and Recommendations. Geneva: World Health Organization; 2013.

Cover of Systematic Screening for Active Tuberculosis: Principles and Recommendations

Systematic Screening for Active Tuberculosis: Principles and Recommendations.

Show details

Annex IIIFlow charts of algorithms for screening and diagnosing tuberculosis (TB) in adults, with modelled yields and predictive values

Screening algorithms options are presented in section9. Each algorithm for adults includes options for the initial diagnostic testing of people whose screening test is positive: either sputum-smear microscopy (conventional light microscopy used to examine direct smears stained with Ziehl–Neelsen, with or without specific sputum-processing methods, or fluorescence microscopy including microscopy with light-emitting diodes) or a rapid molecular test that has been demonstrated to have high accuracy, such as the Xpert MTB/RIF test (Cepheid, Sunnyvale, CA) (or any rapid test recommended by WHO in the future that has the same or better accuracy than the Xpert MTB/RIF ).

Positive or negative diagnostic results may require a repeat test or further diagnostic evaluation using culture, drug-susceptibility testing, clinical assessment, or some combination of these. In these algorithms, culture is not considered for use as an initial diagnostic test because it requires a much longer wait for results (2–6 weeks) than both nucleic acid amplification tests (such as the Xpert MTB/RIF test) and sputum-smear microscopy, both of which can provide final test results in less than 1 day.

The choice of algorithm depends on the risk group being evaluated, the prevalence of TB, the availability of resources and the feasibility (see Sections 8 and 9).

For each algorithm, the following estimates are provided for different prevalences of TB (0.5%, 1% and 2%) in the screened population:

  • negative predictive values of the screening test;
  • pretest probability for the initial diagnostic test;
  • positive predictive value and negative predictive value of the initial diagnostic test among people whose screening test is positive;
  • proportion of true cases detected by the algorithm using outcomes from only the initial diagnostic test;
  • proportion of those with a negative result on the initial diagnostic test that is assumed to undergo further diagnosis with chest X-ray (if not already done) and clinical assessment (see support material at www.who.int/tb/tbscreening);
  • proportion of true cases detected by the algorithm using the results of the initial diagnostic test plus clinical diagnosis in the proportion of those with a negative result on the diagnostic test that is assumed to undergo clinical diagnosis;
  • positive predictive value when using the combination of the initial diagnostic test and clinical diagnosis.

Definitions of estimates used to evaluate the algorithms

Positive predictive value (PPV): the likelihood that a person diagnosed with TB has true culture-positive TB (also the proportion of all detected cases that are true culture-positive TB cases)

Negative predictive value (NPV): the likelihood that a person who is not diagnosed with TB does not have culture-positive TB (1 – NPV = the probability that a person not diagnosed with TB actually has culture-positive TB)

Pretest probability (PTP): the prevalence of culture-positive TB among persons eligible for a test (for a second test in an algorithm this equals the PPV of the previous test); the pretest probability increases with each screening step

Flow charts of algorithms

Algorithm 1a. (chest X-ray and Xpert MTB/RIF not available).

Algorithm 1a

(chest X-ray and Xpert MTB/RIF not available).

Algorithm 1b. (chest X-ray not available, Xpert MTB/RIF available).

Algorithm 1b

(chest X-ray not available, Xpert MTB/RIF available).

Algorithm 1c. (chest X-ray available, Xpert MTB/RIF not available).

Algorithm 1c

(chest X-ray available, Xpert MTB/RIF not available).

Algorithm 1d. (chest X-ray and Xpert MTB/RIF available).

Algorithm 1d

(chest X-ray and Xpert MTB/RIF available).

Algorithm 2a. (chest X-ray and Xpert MTB/RIF not available).

Algorithm 2a

(chest X-ray and Xpert MTB/RIF not available).

Algorithm 2b. (chest X-ray not available, Xpert MTB/RIF available).

Algorithm 2b

(chest X-ray not available, Xpert MTB/RIF available).

Algorithm 2c. (chest X-ray available, Xpert MTB/RIF not available).

Algorithm 2c

(chest X-ray available, Xpert MTB/RIF not available).

Algorithm 2d. (chest X-ray and Xpert MTB/RIF available).

Algorithm 2d

(chest X-ray and Xpert MTB/RIF available).

Algorithm 3a. (Xpert MTB/RIF not available).

Algorithm 3a

(Xpert MTB/RIF not available).

Algorithm 3b. (Xpert MTB/RIF available).

Algorithm 3b

(Xpert MTB/RIF available).

Copyright © World Health Organization 2013.

All rights reserved. Publications of the World Health Organization are available on the WHO web site (www.who.int) or can be purchased from WHO Press, World Health Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland (tel.: +41 22 791 3264; fax: +41 22 791 4857; e-mail: tni.ohw@sredrokoob).

Requests for permission to reproduce or translate WHO publications –whether for sale or for non-commercial distribution– should be addressed to WHO Press through the WHO web site www.who.int/about/licensing/copyright_form/en/index.html).

Bookshelf ID: NBK294078

Views

  • PubReader
  • Print View
  • Cite this Page
  • PDF version of this title (1.9M)

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...