S1126 Immunosuppressive (IS) Therapy Impacts the Results of QuantiFERON® and Tuberculin Skin Test in Routine Screening for Latent Tuberculosis (LTB) in Patients with Inflammatory Bowel Diseases (IBD)

INTRODUCTION: Screening for LTB is mandatory before starting therapy with Tumor Necrosis Factor (TNF) alpha inhibitors. Recently, a whole blood interferon gamma assay (QuantiFERON®) emerged as additional test for screening of LTB usually consisting of tuberculin skin test (TST) and chest X-ray. However, in patients with immunosuppression (IS) both tests might show limitations. AIMS & METHODS: We aimed to compare results from QuantiFERON®, TST and chest X-ray in consecutive IBD patients with or without IS with the indication of anti TNF alpha therapy. Signs indicative of LTB from chest x-ray included granuloma, bihilar lymphadenopathy and pleura scarring. TST was assessed positive if induration ≥5mm appeared after 48-72h of intracutan application of tuberculin /2 units in 0,1ml/ in immunosuppressed and ≥10mm in all other IBD patients. QuantiFERON® was positive if quantitative measurement indicated ≥ 0,35 U/ml. In pts under IS type, dose, and duration of therapy were obtained. RESULTS: In 145 patients all three tests for LTB were performed. QuantiFERON® test failed on samples from 15/145 (10.3%) patients, resulting in 130/145 (89.7%) patients on whom results from all 3 screening tests were available. There were 109 pts (75.2%) with and 36 (24.8%) without IS. Seventy-six patients (52.4%) were under maintenance AZA/6-MP, 49 (33.7%) under steroids ≥10mg daily for ≥ 2weeks and 16 subjects (11%) received infliximab within a median of 8 (6-16) weeks previously. The impact of IS therapy on TST and QuantiFERON® is shown in the table. The median TST induration was 2.11 mm (±5.2) for the entire study population, 2.07 mm (±5) in pts with and 2.22mm in pts without IS (±5.7) (p=0.882), respectively. Among subjects with positive TST median induration was 12.5 mm (±5.3) in IS patients (n=17) and 16mm (±2.4) in pts without IS (n=5, p=0.058). There was a higher rate of positive QuantiFERON® results in patients without IS (p=0.036). CONCLUSION: Our results reveal significant influence of IS on single TST and QuantiFERON® results in IBD patients undergoing screening for LTB and suggest an underestimation of the actual rate of LTB. Therefore, LTB screening might be best performed before IS treatment.