Diagnostic Usefulness of IFN-Gamma Releasing Assays Compared With Conventional Tests in Patients With Disseminated Tuberculosis

Abstract

IFN-gamma releasing assays (IGRAs) such as T-SPOT.TB assay and QuantiFERON-TB In-Tube (QFT-GIT) have yielded promising results for the diagnosis of tuberculosis (TB). However, little is known about the usefulness of these assays for diagnosing disseminated TB. We therefore compared their usefulness with traditional tests in patients with disseminated TB. All adult patients with suspected disseminated TB were prospectively enrolled at a tertiary hospital in an intermediate TB-burden country during a 6-year period. Disseminated TB was defined as involvement of the bone marrow or 2 noncontiguous organs, or presence of miliary lung lesions. A total of 101 patients with confirmed and probable disseminated TB were finally analyzed. Of these 101 patients, 52 (52%) had miliary TB and the remaining 49 (48%) had nonmiliary disseminated TB. In addition, 63 (62%) had no underlying disease. Chronic granuloma with/without necrosis, acid-fast bacillus staining, Mycobacterium tuberculosis PCR, and culture for M tuberculosis were positive in 77% (41/53), 43% (43/101), 70% (67/96), and 72% (73/101), of the patients, respectively. The T-SPOT.TB assay was positive in 90% (91/101) of them. The sensitivity of the T-SPOT.TB assay in patients with miliary TB (90%) was similar to that in patients with nonmiliary TB (90%) (P>0.99). In a subgroup analysis of the 58 patients in whom both QFT-GIT and the T-SPOT.TB results were available, the sensitivity of QFT-GIT (67%) was lower than that of T-SPOT.TB (95%) (P<0.001).In conclusion, T-SPOT.TB assay may be a helpful adjunct test for disseminated TB.