Clinical utility of the QuantiFERON TB-2G test for elderly patients with active tuberculosis

Objective: To evaluate the response to the QuantiFERON-TB-2 Gold (QFT-2G) test (Cellestis Ltd; Carnegie, VIC, Australia) in elderly patients with active tuberculosis (TB) to determine whether the QFT-2G test might be a feasible method for diagnosing TB infection in this group of patients. Methods: The subjects were 30 elderly patients with active TB and 100 younger patients with active TB. The QFT-2G test results were analyzed in relation to combined and separate responses to early secretory antigenic target 6-kD (ESAT-6) protein and culture filtrate protein 10 (CFP-10) antigens. Results: Of the 30 elderly patients with active TB, 27% had a positive tuberculin skin test (TST) result and 77% had a positive QFT-2G test result. Of the 100 younger patients with active TB, 70% had a positive TST result and 87% had a positive QFT-2G test result. Although there was no significant difference between the two patient groups in the positive rate for the QFT-2G test results (p = 0.185), there was a significant difference in the rates of positive TST results between the elderly and younger patients (p = 0.012). The positive test result rate for both E-SAT-6 and CFP-10 antigens in the elderly patients (17%) was significantly lower than that in younger patients (37%; p = 0.038). There was an indeterminate result for the QFT-2G test in five elderly patients, and this might have been related to the presence of lymphocytopenia due to underlying disease. A negative result on the QFT-2G test was detected in two elderly patients, and this might have been related to the severity of the active TB. Conclusion: We confirmed that the QFT-2G test might be a more useful method of diagnosing TB infection than the TST for elderly patients if peripheral lymphocyte counts have been preserved.