Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1400 page)

   
M
.
scrofulaceum
—cervical lymphadenitis

   
M
.
marinum
,
M
.
ulcerans
,
M
.
haemophilum
—skin and superficial infections

   
M
.
xenopi
—pulmonary

   
M
.
genavense
—disseminated and GI disease in immunocompromised patients

   
M
.
malmoense
—pulmonary

MYCOBACTERIUM TUBERCULOSIS
SCREENING INTERFERON-GAMMA RELEASE ASSAY

   Definition and Use

   
M
.
tuberculosis
infection may present with a range of disease syndromes, including acute infection, active infection, latent infection, and reactivation disease. Patients are evaluated on the basis of clinical presentation, epidemiologic risk assessment, radiographic studies, and evidence of host response by screening tests; diagnosis is established by detection of
M
.
tuberculosis
by culture or molecular diagnostic methods.

   In the past, the tuberculin skin test (TST) was used to detect host response, but the recent development of FDA-approved interferon-gamma release assays (IGRAs) has provided an alternative method for detecting immunologic response to
M
.
tuberculosis
antigens. IGRAs may be used in the evaluation of patients for latent or active (acute or reactivation) TB.

Method

   Three FDA-approved IGRAs are currently available.

   IGRAs measure immune reactivity of a patient’s WBCs when challenged with synthetic antigens that are present in all strains of
M
.
tuberculosis
but absent in BCG strains. Immune reactivity is measured by the interferon-gamma concentration, or number of interferon-gamma–producing cells, after exposure of viable WBCs to these antigens.

   Advantages of IGRAs include

   IGRAs require only a single patient visit to conduct the test.