Rapid diagnosis of tuberculosis using the amplification method

BACKGROUND: Amplification methods identify Microbacterium tuberculosis on the basis of genus- or species-specific sequence of bases in nucleic acids which they replete exponentially. The objective of the work was comparison of results of biological samples by the method Gen-Probe Mycobacterium tuberculosis Direct Test (MTD) using amplification of ribosomal RNA and BK by microscopy and cultivation, assessment of standard indicators of their efficiency of the method and analysis of diverging results. METHODS AND RESULTS: During the period between April 19, 1994 and October 19, 1995 a total of 650 specimens from 316 patients examined for suspected tuberculosis were processed. After decontamination the specimens were divided into two portions and examined by the Gen-Probe MTD and by classical BK microscopy and cultivation. 95 specimens were Gen-Probe MTD positive. As compared with BK cultivation the sensitivity of Gen-Probe MTD is 94.7%, the specificity 93.1%, the positive predictive value 56.8% and the negative predictive value 99.5%. Falsely positive were the specimens from 33 patients, most frequently with a diagnosis of tumours, non-specific bronchopneumonias and interstitial pulmonary fibroses. CONCLUSIONS: Gen-Probe MTD is a rapid examination with an equal or higher sensitivity than BK cultivation. The disadvantage is a somewhat lower specificity and higher cost.