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), orthe 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.