[Clinical diagnostic value of the PCR assay for detection of Mycobacterium tuberculosis]

To evaluate the clinical diagnostic value of the PCR assay for detection of M. tuberculosis, a total of 758 samples from 387 patients were assayed by the polymerase chain reaction (PCR) using the IS6110 gene as a target, and the results of the PCR assay were compared with those obtained by conventional culture. The patient's profiles such as clinical situation that required prompt differential diagnosis by the PCR assay, underlying disease and final diagnosis were analyzed. The PCR assay lead to the rapid diagnosis of tuberculosis which was confirmed by culture in all 56 cases including elderly and immunocompromised patients. One hundred and seventy-six of the 231 (76.2%) cases had abnormal shadows in the chest X-ray film that required the PCR assay for diagnosis of tuberculosis and differential diagnosis of pleural effusion, lung cancer or bacterial pneumonia. Negative PCR results were also used when active pulmonary tuberculosis had to be excluded. Forty-nine out of 95 cases (51.6%) with a final diagnosis of tuberculosis were in PCR-negative. The basis of the diagnosis in spite of the PCR negative results included positive culture results (8 cases) and histological findings (9 cases) in other specimens that were not subjected to PCR, radiological findings (24 cases), biochemical characteristics of pleural effusion (6 cases) or cerebrospinal fluid (1 case), and bronchoscopical findings (1 case). In 56 smear-negative patients with final diagnosis of pulmonary tuberculosis, the larger the number of specimens received for the PCR assay from each patient, the higher the frequency of positive cases; with 1, 2 and 3 specimens received for the PCR assay, 13.3% (4/30), 45.5% (5/11) and 60.0% (3/5) of cases were PCR positive, respectively. For the prompt diagnosis of tuberculosis by detection of tuberculous DNA using PCR, it is important to examine appropriate samples from the affected part of the patient and also to repeat the tests especially when the smear is negative.