Clinical evaluation of QuantiFERON®-TB Gold Plus directly compared with QuantiFERON®-TB Gold In-Tube and T-Spot®.TB for active pulmonary tuberculosis in the elderly.

Background: Reduced sensitivity of tuberculosis (TB) interferon-γ release assays (IGRAs) among the elderly has been reported, which is presumably due to diminished immune function. We evaluated the clinical performance of QuantiFERON®-TB Gold plus (QFT-Plus) compared with QuantiFERON®-TB Gold In-Tube (QFT-GIT) and T-Spot®.TB (T-SPOT) in the elderly.

Methods: Blood samples for all three IGRAs were drawn at the same time from all the participants. Both CD4 and CD8 T-cell counts in patients' peripheral blood were also measured.

Results: A total of 142 active pulmonary TB patients (median age: 84, interquartile range; 76-89 years) were recruited. The sensitivities of the tested IGRAs (excluding invalid/indeterminate cases) were as follows: QFT-Plus, 93.6%; QFT-GIT, 91.4%; and T-SPOT 68.1%. QFT-Plus displayed significantly higher sensitivity than T-SPOT (p < 0.00001). All three IGRAs exhibited the same specificity (100%), as assessed using blood samples from healthy, low TB-risk individuals (n = 118; median age: 39, IQR; 32-47 years). Positivity in 43 active TB patients with CD4 T-cell counts <200/μL, 39 of whom were ≥80 years of age, was as follows: QFT-Plus, 83.7%; QFT-GIT, 74.4%; and T-SPOT, 58.1%. The difference between TB2-TB1 of the QFT-Plus assay was statistically correlated with CD8 but not CD4 T-cell counts in blood (r = 0.193, p = 0.0298).

Conclusions: QFT-Plus showed high performance in the detection of TB infection in patients irrespective of their advanced age (≥80 years) or lower CD4 counts. QFT-Plus can be useful for the diagnosis of TB infection in all patients, including those who are elderly and/or immunocompromised.