4
Diagnosis
➤ The panel suggests performing a TST rather than an IGRA in
healthy children <5 years of age for whom it has been decided
that diagnostic testing for LTBI is warranted (C-VL).
• Remarks: In situations in which an IGRA is deemed the preferred diagnostic test,
some experts are willing to use IGRAs in children >3 years of age.
The preceding recommendations are summarized in Figures 1 and 2.
While both IGRA and TST testing provide evidence for infection
with Mtb, they cannot distinguish active from latent tuberculosis.
Therefore, the diagnosis of active TB must be excluded prior
to embarking on treatment for LTBI. This is typically done by
determining whether or not symptoms suggestive of TB disease are
present, performing a chest radiograph and, if radiographic signs
of active tuberculosis (eg, airspace opacities, pleural effusions,
cavities, or changes on serial radiographs) are seen, then sampling is
performed and the patient managed accordingly.
Testing for TB Disease
➤ The panel recommends that acid-fast bacilli (AFB) smear
microscopy be performed, rather than no AFB smear microscopy,
in all patients suspected of having pulmonary TB (S-M).
Remarks: False-negative results are sufficiently common that a negative AFB smear
result does not exclude pulmonary TB. Similarly, false-positive results are sufficiently
common that a positive AFB smear result does not confirm pulmonary TB. Testing of
3 specimens is considered the normative practice in the United States and is strongly
recommended by the Centers for Disease Control and Prevention and the National
Tuberculosis Controllers Association in order to improve sensitivity given the pervasive
issue of poor sample quality. Providers should request a sputum volume of ≥3 mL, but
the optimal volume is 5–10 mL. Concentrated respiratory specimens and fluorescence
microscopy are preferred.
➤ The panel suggests that both liquid and solid mycobacterial
cultures be performed, rather than either culture method alone,
for every specimen obtained from an individual with suspected
TB disease (C-L).
Remarks: The conditional qualifier applies to performance of both liquid and solid
culture methods on all specimens. At least liquid culture should be done on all specimens
since culture is the gold standard microbiologic test for the diagnosis of TB disease.
The isolate recovered should be identified according to the Clinical and Laboratory
Standards Institute guidelines and the American Society for Microbiolog y Manual of
Clinical Microbiolog y.
