Adjunctive role of T-Spot.TB in evaluating active tuberculosis: a retrospective cohort study in a tertiary-care hospital in a low-burden country

Background Although T-Spot.TB is widely used to diagnose Mycobacterium tuberculosis infection, its role in the diagnosis of active tuberculosis (TB) remains controversial. We aimed to evaluate not only the diagnostic performance of T-Spot.TB but also the clinical contexts, in which it might be useful in patients with suspected active TB. Methods In this retrospective study, we included 2224 patients who underwent T-Spot.TB and microbiological testing within 30 days at Chiba University Hospital (2015-2024). Outcomes comprised microbiological and/or pathological confirmation of TB and anti-TB therapy initiation. Results We revealed that 200 (9 %), 2000 (89.9 %), and 24 (1.2 %) patients tested positive, non-positive, and intermediate for T-Spot.TB, of whom we diagnosed active TB in 78 patients (3.5 %), with rates of 27.0 %, 1.1 %, and 8.3 %, respectively. The positive and negative predictive values were 27.0 % and 98.9 %, respectively. In multivariable analysis, younger age and T-Spot.TB positivity were independently associated with active TB. Among T-Spot.TB-positive patients, median time to treatment initiation was 10 days (IQR, 5-23). Conclusion T-Spot.TB may serve as a useful adjunctive diagnostic tool in a tertiary-care hospital in a low-burden country, particularly given its high negative predictive value. The association between T-Spot.TB positivity and active tuberculosis differed by age, with a relatively greater association observed in younger patients. These findings suggest that the clinical utility of T-Spot.TB results may vary by patient characteristics, especially age.