Evaluation of Microscopy, Culture and PCR Assay in the Diagnosis of Extrapulmonary Tuberculosis

Extra pulmonary tuberculosis presents a diagnostic dilemma for both physicians as well as for clinical microbiologists . The laboratory diagnosis of tuberculosis ranges from simple microscopy,culture to complex molecular assays. To evaluate the sensitivity, specificity and turnaround time of microscopy, culture and PCR in the diagnosis of Extrapulmonary tuberculosis & to evaluate the use of PCR in the early diagnosis of Extrapulmonary tuberculosis. A total of 71 samples patients with strong clinical suspicion of extra-pulmonary tuberculosis were processed and evaluated by ZN staining, fluorescent microscopy, LJ culture, BacT Alert culture and PCR. The positivity rates by microscopy, LJ culture, BacT Alert culture and PCR were 11.26%, 8.45%, 14.08% and 14.08% respectively. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of both staining methods was 50%, 92.3%, 37.5% and 95.2% respectively. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of BacT Alert culture was 83.3%, 92.3%, 50% and 98.4% respectively. The recovery rate was higher by BacT Alert culture (90.9%) compared to LJ culture (63.63%). The mean turnaround time for culture positivity was 36.3 days with LJ culture and 14.6 days with BacT Alert culture. The sensitivity, specificity, positive predictive value and negative predictive value of PCR assay was 66.66%, 90.76%, 40% and 96.72% respectively. PCR has high sensitivity, specificity, substantial level of agreement with BacT Alert culture and shorter turnaround time. Therefore, use of PCR in combination with other diagnostic modalities is a useful tool to detect additional EPTB cases which may be missed otherwise.