Comparison of Tuberculin Skin Test and Mycobacterium Tuberculosis-spesific interferon gamma assay for the diagnosis of latent tuberculosis infection in Juvenile idiopathic arthritis

Objectives: Tuberculin skin test (TST) has been used to detect latent tuberculosis infection (LTBI) for about a century. However, the TST has low sensitivity and specificity, and has shown some other limitations. Patients who are at high risk for developing tuberculosis infection should have accurate diagnosis of latent tuberculosis infection.The objective of this study was to compare a M.tuberculosis ?specific IFN-? ELISA (QFT-TB Gold In Tube) (Cellestis Ltd, Carnegie, Australia) test with a classic TST for detection of LTBI in patients with juvenile idiopathic arthritis (JIA).Methods: A cross-sectional study of 39 children with JIA and 40 healthy controls was done. Demographic characteristics, juvenile ıdiopathic arthritis subtypes, medications, tuberculosis contact history, BCG vaccination status was recorded from all patients. Blood was for drawn for the QFT-TB Gold In Tube assay prior to administration of the TST. A positive TST was defined as ?10mm for JIA and ? 15 mm for controls. Statistical analyses were performed using SPSS version 16.0 for Windows.Results: The median TST enduration was 5,8 mm (±5,7mm) for JIA and 10,7 mm (±4,5mm) for the control group, which was istatistically significant (p=0.000). The rate of patients who showed no reaction to TST was 38%, and 93% of which had active disease. One of the two patients who have positive IFN-? results but negative TST were systemic type, other one were polyartricular type JIA. Overall agreement between TST and QFT-G was low both in JIA and control group (k value=0.06 and 0.10, respectively).Conclusion: Tuberculin skin test may be inadequate to diagnose latent tuberculosis infection in JIA patients. The IFN-? assay may be useful to identify false-negative TST response to cases of latent Mycobacterium tuberculosis infection. At the time of diagnosis and especially in patients whom anti-TNF treatment planned to started, IFN-? assays such as the QFT-G in-tube method may be considered in addition to the TST for diagnostic screening and monitoring of LTBI in JIA. Long-term prospective studies are still necessary to appreciate the advantages and the applicability of these tests in pediatrics.