The role of interferon-gamma release assays in the diagnosis of active tuberculosis.

Background: Interferon-gamma release tests are appealing alternatives to the tuberculin skin test (TST) for latent tuberculosis infection. Objectives: To determine the yield of the Quantiferon TB Gold test (QFT-G) in the diagnosis of active tuberculosis disease, with a focus on elderly patients, human immunodeficiency virus (HIV) co-infection, and extra-pulmonary tuberculosis (EPTB). methods: The QFT-G test was performed in 98 patients suspected of having active tuberculosis. The results were evaluated for each subgroup of patients and compared to the results of the TST. results: Active tuberculosis was diagnosed in 92 of the 98 patients. Sixteen (17.3%) were elderly patients (over age 70), 15 (16%) were co-infected with HIV, and 14 (15%) had EPTB. QFT-G was positive in 49 patients (53%) and indeterminate in 4. The results were not significantly affected by HIV coinfection (P = 0.17), old age (P = 0.4), or the presence of EPTB (P = 0.4). There was a good correlation between the TST and the QFT-G test (P < 0.001). In EPTB and in the elderly, the QFT-G test appears to be better than the TST. conclusions: The QFT-G test is suboptimal in its ability to detect active tuberculosis and should not be used to exclude it.