Qualitative and quantitative results of interferon-γ release assays for monitoring the response to anti-tuberculosis treatment.

BACKGROUND/AIMS: The usefulness of interferon-γ release assays (IGRAs) in monitoring to responses to anti-tuberculosis (TB) treatment is controversial. We compared the results of two IGRAs before and after anti-TB treatment in same patients with active TB.

METHODS: From a retrospective review, we selected patients with active TB who underwent repeated QuantiFERON-TB Gold (QFN-Gold, Cellestis Limited) and T-SPOT.TB (Oxford Immunotec) assays before and after anti-TB treatment with first-line drugs. Both tests were performed prior to the start of anti-TB treatment or within 1 week after the start of anti-TB treatment and after completion of treatment.

RESULTS: A total of 33 active TB patients were included in the study. On the QFN-Gold test, at baseline, 23 cases (70%) were early secreted antigenic target 6-kDa protein 6 (ESAT-6) or culture filtrate protein 10 (CFP-10) positive. On the T-SPOT. TB test, at baseline, 31 cases (94%) were ESAT-6 or CFP-10 positive. Most of patients remained both test-positive after anti-TB treatment. Although changes in interferon-γ release responses over time were highly variable in both tests, there was a mean decline of 27 and 24 spot-forming counts for ESAT-6 and CFP-10, respectively on the T-SPOT.TB test ( p < 0.05 for all).

CONCLUSIONS: Although limited by the small number of patients and a short-term follow-up, there was significant decline in the quantitative result of the T-SPOT. TB test with treatment. However, both commercial IGRAs may not provide evidence regarding the cure of disease in Korea, a country where the prevalence of TB is within the intermediate range.