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Red Book addresses TST/IGRA debate

NEW ORLEANS — This year’s Red Book was the first edition that addressed a preference for tuberculin skin testing over interferon-gamma for diagnosing tuberculosis in certain age groups, but questions remain when it comes to diagnosing this illness in pediatrics, according to a speaker here at the 2012 AAP National Conference and Exhibition.

Dwight A. Powell, MD, of Ohio State University, said the 2012 Red Book stated a preference for tuberculin skin tests (TST) over the newer interferon-gamma release assays (IGRAs) in children aged younger than 5 years. In children aged older than 5 years, IGRA is preferred. Both a TST and an IGRA should be used when the initial IGRA test is indeterminate, when the initial TST is negative and the clinician suspects TB disease, according to the Red Book.

Powell said the debate as to which test is better to use in which population comes about because the TSTs lack specificity in populations where the bacillus Calmette-Guérin (BCG) vaccine has been administered.

He urged clinicians to keep in mind the measure of induration, combined with certain risk factors. Powell said it is important to measure the induration, not redness, adding that it also is important to measure transversely to the long axis of the forearm, and induration should be the palpable, hardened area around the injection site.

Induration, with a positive TST test of 5 mm “equals an infection with mycobacteria,” Powell said. Addressing the BCG complication, he said, “If you had a single BCG as an infant, after 5 years, you won’t be over 10 mm, but it is a quandary.”

Powell said there are two IGRAs on the market for diagnosing latent infection, QuantiFERON-TB Gold (Cellestis) and T-SPOT.TB (Oxford Immunotec).

He said studies that have compared IGRAs with skin testing for both sensitivity and specificity have shown “essentially no difference,” with neither being 100% specific or sensitive.

For more information:

Powell DA. Session 2034. Presented at: AAP National Conference and Exhibition; Oct. 20-23, 2012; New Orleans.

Disclosure: Powell reports no relevant financial disclosures.