A Study On Evaluation Of T-SPOT.TB Assay For Diagnosing Active Tuberculosis

BackgroundTuberculosis has always been one of the most important infectious diseases that threaten human health.The traditional techniques for tuberculosis diagnosis lack of sensitivity and specificity.In recent years,T-SPOT.TB as a new method for tuberculosis diagnosis which is based on antigen-specific T cell response,has been developed.However,large-scale prospective study on evaluation of this new method for diagnosing active tuberculosis has not been reported in TB high burden countries.Methods and ObjectiveWe conducted a prospective study enrolling 242 patients with clinically suspected tuberculosis who were admitted in Peking Union Medical College Hospital from December 2005 to December 2008.We assessed the value of peripheral blood T-SPOT.TB assay for the diagnosis of active tuberculosis through comparing T-SPOT.TB test results and final clinical diagnosis in routine clinical practice.Results70 patients had a final diagnosis of active tuberculosis.Sensitivity of T-SPOT.TB for active tuberculosis was 82.9%(95%confidence interval[CI],74 to 91.7%,),and specificity was 55.3%(CI,46.9 to 63.7%),positive predictive value was 49.6%(CI,40.6 to 58.6%),negative predictive value was 85.9%(CI,78.5 to 93.3%), positive likelihood ratio was 1.85(CI,1.72-2.04),and negative likelihood ratio was 0.31(CI,0.18-0.41).30 patients were bacteriologically or histologically confirmed active tuberculosis,sensitivity of T-SPOT.TB was 96.7%(CI,83 to 100%);40 patients were diagnosed as highly probable tuberculosis,sensitivity of T-SPOT.TB was 72.5%(CI,56 to 85%).Active tuberculosis was diagnosed in 46 of 162 non-dropsy of serous cavity patients,sensitivity of T-SPOT.TB was 91.3%(CI,79 to 97%),specificity was 54.3%(CI,45.3 to 63.3%),positive predictive value was 44.2%(CI,34.2 to 54.2%),negative predictive value was 94%(CI,88.3 to 99.7%),positive likelihood ratio was 1.99(CI,1.82-2.27),and negative likelihood ratio was 0.16(CI,0.01-0.27); tuberculous serositis was diagnosed in 24 of 40 dropsy of serous cavity patients, sensitivity of T-SPOT.TB was 66.7%(CI,45 to 84%),specificity was 62.5%(CI,35 to 85%),positive predictive value was 72.7%(CI,50 to 89%),negative predictive value was 55.6%(CI,31 to 78%),positive likelihood ratio was 1.78(CI,1.40-3.47),and negative likelihood ratio was 0.53(CI,0.37-0.61).ConclusionHigh NPV of T-SPOT.TB for the diagnosis of active tuberculosis suggests the supplementary role of the test for the diagnostic exclusion of active TB,although the low PPV limits its usefulness in routine clinical practice in China,where the prevalence of latent TB infection is high.