National hospital for tuberculosis (TB) and rheumatoid arthritis (RA) in Japan.
To compare two interferon-γ release assays (IGRAs), QuantiFERON
QFT and T-SPOT were conducted concurrently in 230 prospectively enrolled RA patients.
There were no active TB patients. The percentage of QFT- and T-SPOT-positive patients was respectively 8.3% and 5.7%. In patients aged ⩾60 years, these proportions were respectively 12.3% and 7.2%. The percentage of QFT positivity and T-SPOT positivity at age <60 years was respectively 2.2% and 3.3%. After multivariate logistic analysis for QFT positivity, age ⩾60 years and TB suspected based on chest X-ray were selected as independent factors, with adjusted odds ratios of respectively 4.73 and 3.25. No factors were selected for T-SPOT positivity.
QFT had a higher positivity rate. In the light of the previous estimated rate of LTBI in Japan, both IGRAs underestimate LTBI, and neither IGRA has enough capability to detect LTBI.