To evaluate the performance of an interferon-γ release assay (IGRA) versus the standard tuberculin skin test (TST) as a screening tool for latent tuberculosis (TB) infection prior to the initiation of anti-tumor necrosis factor therapy in patients with autoimmune inflammatory diseases.
This integrated analysis involved screening of patients with rheumatoid arthritis, those with psoriatic arthritis, and those with ankylosing spondylitis from phase III trials of golimumab. The IGRA used to screen for latent TB was the QuantiFERON-TB Gold In-Tube test.
In this pooled analysis, 2,282 patients underwent both IGRA and TST screening prior to golimumab treatment. Among these patients, 13.8% had at least one test yielding positive findings for latent TB, including 9.4% with positive results by TST, 7.0% with positive results by IGRA, and 2.6% with positive results on both tests. The rate of indeterminate results for TB on IGRA was 1.8%. Agreement between the TST and IGRA results, measured by the kappa coefficient, was 0.22 (95% confidence interval 0.157-0.279; P=0.021). Among the patients with positive IGRA findings, 36.9% had positive TST findings. Among the patients with positive TST findings, 27.4% had positive IGRA findings. Overall, 781 (34.2%) of the 2,282 patients had previously received the bacillus Calmette-Guérin (BCG) vaccine; among this vaccinated group, the rate of positivity for latent TB by TST was 15.2% (119 of 781), compared to a rate of positivity of 9.1% (71 of 781) by IGRA (P=0.0002). Among patients who had not received the BCG vaccine, the rate of positivity by TST was 5.0% (62 of 1,248) and the rate of positivity by IGRA was 5.8% (72 of 1,248) (P=0.3745). When the IGRA was repeated in patients whose results were initially indeterminate, the rate of indeterminate IGRA findings for latent TB was much lower than has been previously reported.
In the absence of a true gold standard test for latent TB infection, results of this comparison of IGRA and TST in a large cohort of patients with rheumatic diseases suggest that the IGRA provides greater specificity and possibly greater sensitivity than the TST.