PCR diagnosis of tuberculosis--experience in India

Rapid and accurate diagnosis of tuberculosis is the cornerstone of global tuberculosis control programmes. With increasing incidence of tuberculosis epidemics, the low sensitivity and the length of time taken by traditional diagnostic modalities have hampered the efforts to interrupt disease transmission. Introduction of Polymerase Chain Reaction has enhanced the diagnostic predictability of the disease especially in the extrapulmonary, paucibacillary samples. High specificity and sensitivity have been reported in different samples. The technique is capable of picking as few as ten to fifty tubercle bacilli. When PCR technique is performed under quality controlled conditions, false negatives (due to underfined polymerase inhibitors) and false positives (due to cross contamination during sample collection or in the laboratory) can easily by avoided. Samples from sites with a possible latent infection focus or DNA from dead bacilli may give a positive reaction. The use of PCR with traditional diagnostic tools along with clinical presentation can prove helpful in patients presenting with a diagnostic dilemma.