Positive conversion of interferon-γ release assay in patients with rheumatic diseases treated with biologics

The objective of this study is to investigate whether the type of biologics (TNFi or others) or type of rheumatic diseases (RA or AS) influence the conversion rate of initially negative tuberculosis (TB) screening test results. A total of 119 patients with RA or AS who had negative baseline interferon-γ release assay (IGRA) results assessed by QuantiFERON-TB Gold in tube (QTF-GIT) were included. All patients received biologic agents, and rescreening with QTF-GIT was performed after a median of 25.9 months from the baseline test. Clinical characteristics and IFN-γ levels were compared between converters and non-converters. Logistic regression analysis was performed to identify factors associated with positive conversion. IGRA conversion was found in 14 of 119 patients (11.8%). The converters were older (53.4 ± 14.2 vs 44.4 ± 15.5 years, p = 0.040), had higher baseline TB-specific IFN-γ responses (0.105 [0.018-0.205] vs 0.010 [0.000-0.035] IU/ml, p = 0.001) and higher incidence of active TB (14.3% vs 0.0%, p = 0.013). The number of patients with RA or AS was 9 (64.3%) or 5 (35.7%) in converters, and 45 (42.9%) or 60 (57.1%) in non-converters. In terms of use of biologics, TNFi of monoclonal antibody form was less commonly used in the converters (p = 0.024). In the logistic regression analysis, type of disease and type of biologics used were not associated with IGRA conversion, whereas baseline TB-specific IFN-γ response was significantly associated with IGRA conversion (OR 1.083, 95% CI 1.019-1.151, p = 0.011). Serial monitoring of LTBI with IGRA retesting is needed during biologic treatment, regardless of the type of rheumatic diseases or type biologics used.