A comparative study of the Diagnosis of Pulmonary Tuberculosis using conventional tools and Polymerase Chain Reaction.

ABSTRACT

Results: Total cases considered to be positive for tuberculosis by all criteria was 71. PCR detected 98% of ‘culture positive’, 97% of ‘smear positive, culture positive’, and 100% of ‘smear negative’ culture positive samples. PCR was also positive for 86% of smear negative samples, from tuberculosis suspects diagnosed on the basis of other routine diagnostics and supporting clinical evidence. Seventeen samples were positive only by PCR but based on clinical parameters only 7 were considered as true positives. The sensitivity of PCR was 91.5% compared to 51% for smear microscopy and 68% for sputum culture. This was due to the fact that PCR could pick up bacterial DNA even from saliva mixed sputum specimens, which are generally not considered appropriate for microbiology. The specificity of PCR (86%) was found to be lower than other diagnostic tests mainly due to lack of a suitable gold standard to assess its efficiency. This is an important limitation in evaluation of the test. Conclusions: PCR using MPB64 primers has potential and can be a useful adjunct to diagnose clinical tuberculosis, particularly in smear negative paucibacillary cases. However, the major limitation of PCR results from the absence of a suitable gold standard by which to evaluate the results.