Performance of interferon-gamma release assay for tuberculosis screening in inflammatory bowel disease patients

Screening for latent tuberculosis (TB) is mandatory in inflammatory bowel disease (IBD) before starting anti-tumor necrosis factor therapy. Data on the utility of screening tests in populations with moderate background risk of TB are limited. This study aims to evaluate the performance of interferon-gamma release assay (IGRA) with QuantiFERON-TB Gold in IBD patients in a TB endemic region. Two hundred sixty-eight consecutive adult IBD patients and 234 healthy controls were prospectively recruited. Detailed clinical history, chest x-ray findings, and IGRA results were documented for all individuals. The IGRA positive rates between IBD patients, with or without immunosuppressant, and healthy controls were compared. The IGRA result was positive in 21.9% of IBD patients and 19.2% of healthy controls (P = 0.535). IBD patients on immunosuppressive therapy had a significantly lower IGRA positive rate (13.0% versus 29.6%; P = 0.002) compared with immunosuppressant-naive IBD patients. This difference seemed to be most prominent for patients taking azathioprine (11.8% versus 27.3%, P = 0.006). IGRA results are negatively impacted by immunosuppressive therapy. Current guidelines suggesting TB screening before anti-tumor necrosis factor therapy may be inadequate in patients already on immunosuppressive drugs. Latent TB testing seems best performed before the initiation of immunosuppressive therapies in IBD patients.