P057 - Usefulness of the Quantiferon TB Gold Test in assessing the necessity for TB prophylaxis in IBD patients treated with biologicals

Abstract

INTRODUCTION: Screening for latent tuberculosis is required prior to commencement of anti-TNF-alpha therapy in patients with IBD. However, the protein purified derivative (PPD) test is of low sensitivity and specificity in populations with high frequency of immunosuppressive treatment and previous BCG vaccination. AIMS &METHODS:We aimed to evaluate the usefulness of the Quantiferon TB Gold test in assessing the true necessity for TB prophylactic treatment. We performed an investigation on a group of our IBD patients by performing the screening for TB with all three tests: tuberculin skin test (PPD), chest X-ray (CXR), and Quantiferon TB Gold test (QTB). The primary goal of this study was to look at results of QTB in patients with slightly positive PPD (induration 5-15 mm), in whom the TB prophylaxis with isoniazide (INH) is recommended. In case of QTB negativity, this potentially hepatotoxic agent may be avoided, provided the CXR is also normal. RESULTS: One hundred and thirty four patients with both Crohn disease (CD) and ulcerative colitis (UC) were enroled. Among them, 24 (18%) had sligh positivity of the PPD, i.e. they had induration between 5-15 mm. Of these 24 subjects, 19 (79%) were QTB negative, 4 (17%) indeterminate, and 1 (4%) was QTB positive, respectively. None of 19 QTB negative patients was adviced by the pneumologist to be prophylactically treated with INH. On the other hand, there were 3 QTB positive patients among subjects with normal PPD (induration below 5 mm), all of them had also normal CXR. Despite this, they were given INH according to pneumologists' recommendation. Relatively more patients with QTB negativity were seen among those with normal PPD (96/104, 92%), as compared with group with slight PPD positivity (19/24, 79%). There was no positive QTB seen in patients with high PPD positivity (induration above 15 mm). CONCLUSION: Using the Quantiferon TB Gold test, the prophylactic INH administration could be avoided in almost 80% of patients with slightly positive PPD test. To the contrary, some 3% of PPD negative patients were identified to be at higher risk for TB, and therefore treated with INH.