Diagnosis of pulmonary tuberculosis by polymerase chain reaction for MPB64 gene: an evaluation in a blind study

Polymerase chain reaction (PCR) has been found to be a sensitive and rapid method to confirm a clinical diagnosis of tuberculosis. We evaluated PCR for M. tuberculosis complex specific MPB64 gene for the diagnosis of pulmonary tuberculosis, in a double blind study. One hundred and eighty-two clinical samples (sputum, bronchioalveolar lavage and pleural fluid) from patients with a clinical diagnosis of pulmonary tuberculosis and 72 samples from patients with non-tubercular pulmonary lesions and normal healthy individuals were included. The samples were coded and clinical details were concealed from the laboratory, where conventional diagnostic methods and PCR were carried out independent of each other. On decoding and analysing the data, PCR was positive in 59% of single sputum samples from clinically diagnosed pulmonary tuberculosis, while M. tuberculosis could be grown in 18% of the samples. PCR could identify M. tuberculosis in 81.8% of the culture positive sputum samples. PCR was also positive in 71.4% of bronchioalveolar lavage (BAL) fluid and 60.7% pleural fluid samples from clinically suspected cases, which were mostly culture negative. On comparison with response to treatment, PCR was positive in 79.5% of patients who improved on anti-tuberculosis treatment, with a positive predictive value of 92%. PCR for MPB64 gene provides a useful alternative for the diagnosis of pulmonary tuberculosis from sputum and paucibacillary samples like BAL and pleural fluid in which conventional methods show low sensitivity, especially in areas from which strains show a low copy number of other PCR targets like the IS 6110 insertion sequence.