The impact of previous tuberculosis history on T-SPOT.TB® interferon-gamma release assay results.

SETTING: Seoul National University Bundang Hospital, a tertiary referral hospital in Korea. OBJECTIVE: To evaluate whether previous tuberculosis (TB) history has a long-term effect on T-SPOT.TB® results after anti-tuberculosis treatment. DESIGN: We retrospectively reviewed 489 adults (age ≥18 years) who underwent T-SPOT.TB as part of their evaluation between January 2008 and July 2009. RESULTS: Among 489 subjects analysed, 369 were finally included. Active TB was diagnosed in 121/369 (32.8%). T-SPOT.TB was positive in 110 (90.9%) active TB patients. Of the 248 subjects without active TB, T-SPOT.TB positivity was significantly different between the 51 patients with a previous TB history and the 197 without (84.3% vs. 26.9%, P < 0.001). The difference in T-SPOT.TB positivity between the 51 non-active TB patients with a TB history and the 121 active TB patients was not statistically significant (84.3% vs. 90.9%, P = 0.208). Among the 51 non-active TB individuals with a TB history, the mean time since anti-tuberculosis treatment was 22.7 years (range 1-59); this had no correlation with total region of difference 1 (RD1) spot-forming cells (r = -0.076, P = 0.597). CONCLUSION: T-SPOT.TB has a limited role in the diagnosis of TB infection in individuals with a previous history of TB.