CLINICAL UTILITY OF A COMMERCIAL TEST BASED ON THE POLYMERASE CHAIN-REACTION FOR DETECTING MYCOBACTERIUM-TUBERCULOSIS IN RESPIRATORY SPECIMENS

Several studies have reported using methods based on polymerase chain reaction (PCR) to detect Mycobacterium tuberculosis in respiratory tra ct specimens. However, little is known about the actual clinical utili ty of PCR-based tests, and it is uncertain if PCR technology can be tr ansferred to the clinical laboratory. To determine its utility, we eva luated a commercially developed PCR test system in a clinical laborato ry using consecutive respiratory tract specimens. Microscopic examinat ion of smears stained with acid-fast bacilli (AFB), culture, and a PCR -based test (Amplicor (TM) Mycobacterium tuberculosis assay; Roche Mol ecular Systems) were used to evaluate 535 consecutive sputum and bronc hoalveolar ravage specimens from 227 patients. A clinical case definit ion of tuberculosis was used as the reference-standard to determine th e utility of all diagnostic tests. For all specimens from patients wit h a new or a treatment-failure case of pulmonary tuberculosis, the pos itivity rate of PCR (58%) was similar to that of culture (56%) (p > 0. 90) and substantially greater than microscopic examination of AFB-stai ned smears (22%) (p < 0.001). PCR and culture detected M. tuberculosis in 46 and 43%, respectively, of the specimens from patients who did n ot have AFB on microscopic examination of their respiratory tract spec imens (p > 0.90). PCR had a false positive rate of 0.8%. In several in stances, PCR detected M. tuberculosis when culture did not, and vice v ersa. The clinical utility of this PCR-based test is similar to that o f culture for detecting M. tuberculosis in respiratory tract specimens . This test could be integrated into the operations of a clinical labo ratory and it can detect M. tuberculosis within 6 h after specimen dec ontamination.