A comprehensive comparison of pcr based assay versus microscopy & culture in the diagnosis of tuberculosis in different clinical specimens

Abstract

Background: The laboratory diagnosis of tuberculosis ranges from simple microscopy, culture to complex molecular techniques. Rapid diagnosis is important since conventional techniques have limitations. Aims: To evaluate the efficacy of PCR using genus specific and species specific primers versus microscopy and culture in the diagnosis of tuberculosis in different clinical samples. Methods: A total of 125 clinical samples were processed for the detection of Mycobacterium tuberculosis by smear, culture & PCR in the diagnosis of tuberculosis. Results: The overall sensitivity, specificity, PPV and NPV of PCR were 75 %, 88%, 62.5% and 93.42% respectively. PCR done on non tuberculous patients were negative thus showing the specificity of 100%. PCR sensitivity in pulmonary & extra pulmonary clinical samples were 83.33% and 71.42% respectively a relatively higher value than other tests. Out of eight smear positive-culture positive (SP-CP) & twelve smear negative –culture positive (SN-CP) specimens, PCR detected 87.50 % & 66.66% respectively. Conclusions: This study showed that PCR can serve as a useful complement to clinical diagnosis. PCR can be useful in detecting the cases in extra pulmonary specimens which may be missed by smear & or culture. The PCR based assay cannot be used reliably alone as a sole diagnostic tool in the diagnosis of tuberculosis, it has to be performed in conjunction with microscopy & culture methods and interpreted with the clinical settings.