Factors impacting the results of interferon-γ release assay and tuberculin skin test in routine screening for latent tuberculosis in patients with inflammatory bowel diseases

Abstract

Screening for latent tuberculosis (LTB) including chest x-ray, tuberculin skin test (TST), and facultative whole blood interferon-γ assay (IGRA) is part of routine management in inflammatory bowel disease (IBD) patients before starting therapy with tumor necrosis factor (TNF)-α inhibitors. However, in patients with immunomodulators (IM) TST and IGRA might show limitations. We aimed to evaluate the results from an IGRA (QuantiFERON-TB Gold in Tube) and TST as well as their concordance in 208 consecutive IBD patients with indications for anti-TNF-α therapy. Associations of both tests with risk factors for LTB were determined by logistic regression. During screening, 149 patients (71.6%) were under IM therapy. In 26 (12.5%) patients TST was positive, whereas 15 (7.2%) patients showed a positive result from IGRA. IGRA failed on samples from 16/208 (7.7%) patients, resulting in 192/208 (92.3%) patients in whom results from both screening tests were available. Correlation between IGRA and TST results was fair (84.9%, κ = 0.21). The presence of risk factors for LTB showed association with positive results of TST (odds ratio [OR] 3.7, 1.5-9.6) and IGRA (OR 3.5, 1.2-11.3). TST was associated furthermore with age (OR 1.06, 1.02-1.10) and signs indicative of LTB in chest x-ray (OR 4.9, 1.1-19.9). The IGRA was negatively influenced by IM therapy (OR 0.3, 0.1-0.9). Our study reveals that results of IGRA are negatively affected by IM therapy. Thus, current guidelines for TB screening prior anti-TNF-α therapy appear inaccurate in patients under IM. Therefore, LTB screening might be best performed prior to initiation of IM treatment.