An evaluation of the sensitivity, specificity and positive predictive value of CB-NAAT testing in the diagnosis of Tuberculous Pleural Effusion
Abstract
The diagnosis of TB pleural effusion with microbiological confirmation is a challenging task it being a paucibacillary infection and most cases are diagnosed clinically and empirically started on anti tubercular drugs. We studied the diagnostic accuracy of Gene Xpert MTB/Rif assay in the diagnosis of TB pleural effusion by comparing it with clinically confirmed cases that were cured by anti tubercular drugs and also with MGIT960 liquid culture results. In our study we found the sensitivity of Gene Xpert to be 24.71% (95% CI = 15.99% to 35.25%) and specificity to be 100% (95% CI = 80.49% to 100%) by including all cases diagnosed and confirmed clinically. The positive predictive value was 100% and negative predictive value was 20.99% (95% CI = 19.04% to 23.08%) giving the accuracy at 37.25% (95% CI = 27.88% to 47.39%). However if only microbiologically confirmed cases were used to define cases for calculating the accuracy of Gene Xpert, the sensitivity was calculated to be 94.74% (95% CI 73.97% to 99.87%) and specificity was 96.51% (95% CI = 90.14% to 99.28%). The positive predictive value was 85.71%(95% CI = 66.26% to 94.83%) and the negative predictive value was 98.81% (95% CI = 92.49% to 99.82%) giving a diagnostic accuracy of 96.19%(95% CI = 90.53% to 98.95%). Also the microbiological positivity of Tuberculous pleural effusion was considerably higher in HIV positive patients (P=0.004; 95% CI =17.512% to 69.246%).To conclude Gene Xpert MTB/Rif cannot be solely relied on to make or exclude a diagnosis of Tuberculous Pleural effusion and clinical characteristics along with biochemical tests like ADA have to be taken into consideration to make a final diagnosis of pleural Tuberculosis.
Keywords: Tuberculous Pleural Effusion, Gene Xpert MTB/Rif, Sensitivity, Specificity