Background and aims: There are few data available on the effect of immunomodulator/biological therapy on the accuracy of the tuberculin skin test (TST) and interferon-gamma release assay (IGRA) in BCG-vaccinated immunosuppressed patients with inflammatory bowel disease (IBD). Our aim was to define the accuracy, predictors and agreement of TST and IGRA in a BCG-vaccinated immunosuppressed referral IBD cohort.
Methods: 166 consecutive moderate-to-severe IBD patients (122 Crohn's disease, CD and 44 ulcerative colitis, UC) were enrolled in a prospective study from three centers. Patients were treated with immunosuppressives and/or biologicals. IGRA and TST were performed on the same day. Both in- and outpatient records were collected and comprehensively reviewed.
Results: TST positivity rate was 23.5%, 21.1%,14.5% and 13.9% when cut-off values of 5, 10, 15 and 20mm were used. IGRA positivity rate was 8.4% with indeterminate result in 0.6%. Chest X-ray was suggestive of latent tuberculosis in 2 patients. Correlation between TST and IGRA was moderate (kappa: 0.39-0.41, p<0.001). In addition, a cut-off of 14 and 17mm for TST was defined to identify IGRA positivity in a ROC analysis (AUC: 0.76, p=0.03). TST and/or IGRA positivity was not influenced by medical therapy or disease phenotype. Importantly, smoking was identified as a risk factor for TST but not IGRA positivity (OR: 2.70-5.02, p<0.01, for TSTcut-offs=5-20mm).
Conclusion: TST and IGRA tests are partly complimentary methods, and additional testing by TST (with a cut-off of >15mm) should be considered to identify patients at risk for latent TB. Accuracy is satisfactory in BCG-vaccinated, immunosuppressed IBD patients. Smoking is a risk factor for TST positivity.