Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1401 page)

   Results are available within 24 hours, which may facilitate patient evaluation and contact investigation.

   IGRA testing does not boost the immunologic response in subsequent tests.

   Prior BCG vaccination does not cause false-positive reaction in IGRAs.

   The assessment of IGRA test accuracy depends on the populations studied, the comparator method, and other factors. In general, the sensitivity of the IGRAs is high and comparable to TSTs. Studies suggest that the specificity of IGRAs is slightly higher than the specificity of TSTs. IGRAs may be used and considered acceptable medical and public health practice in all situations in which the CDC recommends TST to aid in the diagnosis of TB.

   IGRA assays (and TSTs) are recommended only for patients with a significant prior probability of tuberculosis; routine patient testing is not recommended. If indicated, either TST or IGRA may be used.

   IGRA testing may be recommended after initial TST in special circumstances:

   If the initial, primary test is negative, and

   The risk for poor patient outcome (severe or progressive disease) is high, as for young children or HIV-infected patients.

   The clinical suspicion for TB, based on other criteria, is high.

   A positive result from a second test would be interpreted as increased sensitivity for detection of infection.

   If the initial, primary test is positive, and

   Additional evidence of infection may encourage a patient’s acceptance of the diagnosis and compliance with therapy.

   A negative result would establish a false-positive TST result in patients with a low probability of tuberculosis based on other factors.