Usefulness of interferon gamma release assay in the diagnosis of latent tuberculosis infection in patients with rheumatoid arthritis

Abstract

Use of anti-TNF-α agent increases the risk of reactivation of latent tuberculosis infection (LTBI) and detecting LTBI before using anti-TNF-α agent is mandatory. Tuberculin skin test (TST) is a traditional method for detecting LTBI, which is reported to be attenuated in patients with rheumatoid arthritis (RA). Interferon gamma release assay (IGRA), a novel T-cell based assay is reported to retain its sensitivity in the immunocompromised patients. The aim of this study was to determine whether IGRA shows superior performance than TST in patients with RA in South Korea. One hundred and twenty one patients with RA and 55 age- and sex- matched control patients who did both TST and Quantiferon TB gold-In-Tube (QFT-GIT) in Severance Hospital were retrospectively reviewed. TST was done by the Mantoux method using RT-23 2TU. Indurations larger than 10 mm were considered as positive. QFT-GIT was performed according to the manufacturer’s instructions. The rates of positive results in TST (33.3% vs. 43.4%) and QFT-GIT (35.9% vs. 41.5%) were not significantly different between RA and control group. However, the median induration size of the patients taking disease modifying anti-rheumatic drugs (DMARDs) was significantly smaller than those of the control group [1 (0~30) mm vs. 6 (0~24) mm, p<0.05] and the rate of positive result in TST showed a trend to be decreased as compared to that of the controls (27.6% vs. 39.6%, p=0.078), while the rate of positive results in QFT-GIT did not differ between the two groups. The agreement between TST and QFT-GIT in RA group was moderate (κ=0.557) and that of the controls was substantial (κ=0.616). The agreement between TST and QFT-GIT was poorer in the RA group taking DMARDs (κ=0.396) than in the DMARD naïve RA group (κ=0.702). Twelve patients underwent follow-up TST. Of the nine patients with negative TST result at baseline, four patients showed a positive conversion at follow-up and three of them had positive QFT-GIT results at baseline. Seven patients underwent follow-up QFT-GIT. The results of follow-up QFT-GIT in seven patients remained unchanged. These data suggest that QFT-GIT shows superior performance in patients with RA taking DMARDs. QFT-GIT may have a value in the diagnosis of LTBI in patients with RA.