P-092 QuantiFERON TB Gold Testing for Latent Tuberculosis is More Frequently Indeterminate in Patients with Inflammatory Bowel Disease

Abstract

BACKGROUND: Screening for latent tuberculosis is mandatory prior to the initiation of biologic therapy for inflammatory bowel disease (IBD). Testing has been traditionally performed with the tuberculin skin test (TST) but is often being replaced by the QuantiFERON TB gold test (QFT-G), an interferon-gamma release assay. However, the performance of QFT-G has not been completely validated in patients with inflammatory bowel disease. We aimed to assess the rate of indeterminate QFT-G in patients with IBD and distinguish risk factors that contribute to this result. METHODS: We performed a retrospective chart review analyzing the Henry Ford Health System clinical database for patients with a diagnosis of IBD who underwent QFT-G testing between January 1, 2005 and July 1, 2013. We obtained demographic and clinical information, including exposure to IBD medications as well as risk factors for tuberculosis, such as homelessness, incarceration, or immigration from an endemic region. RESULTS: A total of 117 IBD patients (mean age = 43.7 ± 16.7, 41.9% male and 49.6% caucasian) were included in the study. The overall rate of indeterminate QFT-G was 19.7% (23 patients). Concomitant medications at the time of testing included: oral or intravenous steroids (n = 37, 31.6%), immunomodulators (n = 32, 27.3%), and biologics (n= 41, 35.1%). In patients with indeterminate QFT-G results, 43.5% were receiving steroids, 21.7% were receiving immunomodulators, and 30.4% were receiving biologics. Steroid use was more likely to result in an indeterminate QFT-G (OR 1.85, (95% CI = 0.72-4.73)) but did not reach statistical significance (P = 0.195). Biologics and immunomodulators did not affect QFT-G results (OR 0.77, P = 0.5; OR 0.69, P = 0.6; respectively). Poor agreement was found between QFT-G and TST results (κ = 0.14). Risk factors for tuberculosis did not affect the rate of indeterminate test results. CONCLUSIONS: The rate of indeterminate QFT-G is exceedingly high in patients with IBD. This phenomenon may be due to medication use or the disease itself. Steroid use may increase the likelihood of an indeterminate result.