Performance of T-SPOT.TB Assay in Screening for Tuberculosis Infection among Patients with Systemic Autoimmune Diseases
|Author||Koussougbo Ouma Devi（WuMa）|
|School||Central South University|
|Keywords||systemic autoimmune diseases tuberculosis infection Tuberculin Skin Test T-SPOT.TB Tuberculosis antibodies|
Objective:Patients with systemic autoimmune diseases (SADs) such as Rheumatoid Arthritis(RA), Systemic Lupus Erythematous (SLE), Scleroderma (SSc), inflammatory myositis and the vasculitis are at a high risk of tuberculosis infection(TB).The reasons behind this tendency are firstly patient with SADs have impaired immune function, secondly long standing treatment with glucocorticoids, immunosuppressant, tumor necrosis factor alpha(TNF) inhibition therapy lead to weakened immune response, and thirdly due to the high prevalence of tuberculosis in China. SAD patients with TB,because of prolonged use of steroids, often present with atypical clinical signs of fever, weight loss, dry cough and headache, and hence make it difficult to distinguish between TB and SAD flares.Henceforth, a more sensitive and specific diagnostic tool is needed.. Tuberculin Skin Test (TST) has been used as a traditional method for screening tuberculosis infection. However the sensitivity and specificity of TST is affected by previous Bacille Calmette Guerin (BCG) vaccination and is low in immunosuppressed patients. T-SPOT.TB is an interferon gamma released assay developed as new tool for screening tuberculosis infection. The objective of this study is to analyze the performance of T-SPOT.TB compared to TST in screening tuberculosis infection among patients with systemic autoimmune diseases in a region with a high TB prevalence.Methods:98patients were prospectively recruited. They were divided into two groups, one with a systemic autoimmune disease (SAD) and one without (non SAD group). T-SPOT.TB, TST, full blood count,Acid Fast Staining,culture for Mycobacterium Tuberculosis,Tuberculosis antibodies, Chest X-ray and/or CT lungs were performed on all patients. An interview questionnaire was set up to document all basic demographic data and information regarding Bacille Calmette Guerin(BCG) vaccination, past history of TB, history of living with TB contact and drugs historyResults:The sensitivity of T-SPOT.TB among patients with SADs having active TB was55%and specificity91.7%, that of TST was40%and83.3%.The Positive Predictive Value (PPV) for T-SPOT.TB was73.3%and that of TST was50%.The Negative Predictive Value(NPV) for T-SPOT.TB was83%and that of TST was65%.The kappa coefficient of agreement between T-SPOT.TB and TST was0.206.Conclusion:1. T-SPOT.TB performed better than TST in screening for active tuberculosis infection in patients with systemic autoimmune diseases as the sensitivity, specificity, PPV and NPV of T-SPOT.TB were greater than that of TST.2Age affected TST performance but did not influence T-SPOT.TB assay3.Use of glucocorticoids, immunosuppressant and tumor necrosis factor alpha (TNF) inhibition therapy did not affect T-SPOT.TB and TST performance.