SAN FRANCISCO – Interferon-gamma release assay tests appear to be better than tuberculin skin tests for picking up latent TB in solid organ transplant candidates, according to Dr. Shimon Kusne.
It’s not just because of IGRA’s well-known benefits—as a blood test, results are known after one visit so patients don’t need to return for skin spots to be read, and there are no false positives in patients vaccinated against TB or exposed to environmental strains of mycobacterium.
Instead, IGRA tests simply seem to be better at picking up latent TB, Dr. Kusne, professor of medicine in the division of infectious diseases at the Mayo Clinic Hospital in Phoenix, said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.
He and his colleagues gave 179 kidney, liver, or heart transplant candidates TB skin prick tests and two IGRA tests, the QuantiFERON-TB Gold In-Tube test (QFT-GIT) and the T-Spot test.
QFT-GIT was 2.74 times more likely to be positive than tuberculin purified protein derivative skin tests and T-Spots were 3.10 times more likely to be positive. The findings were statistically significant.
"It may be that IGRA is better in these immune-suppressed hosts. Time will tell," said Dr. Kusne, because these tests are relatively new.
IGRA tests appear to be a fine-toothed comb; positive tests might turn negative the second time around in a small minority of patients. What that means, exactly, still needs to be worked out (Chest 2012;142:55-62). For now, the Centers for Disease Control and Prevention is okay with hospitals checking for latent TB with either IGRA or skin tests in most cases, he said.
Even so, the Mayo Clinic has moved away from skin tests in transplant candidates. "I think mainly it’s because CDC has said it’s okay to use either and because many [patients] come to get their [skin test] and then disappear," Dr. Kusne said.
"But cost is always a consideration, too. It’s very cheap" to do a skin test, he said at the meeting, which was sponsored by the American Society for Microbiology.
Dr. Kusne said he had no relevant financial disclosures.