DIAGNOSTIC-VALUE OF AN AMPLIFICATION METHOD (GEN-PROBE) COMPARED WITHTHAT OF CULTURE FOR DIAGNOSIS OF TUBERCULOSIS

Five hundred fifty respiratory and nonrespiratory specimens from 340 p atients were analyzed by comparing the Gen-Probe Amplified Mycobacteri um Tuberculosis Direct Test (MTD) with conventional culture, which was the method of reference, for the detection of the Mycobacterium tuber culosis complex, After resolution of discrepant results by retesting t he samples and reviewing the patients' clinical histories, a total of 60 respiratory specimens were MTD and culture positive, 347 were MTD a nd culture negative, 4 were MTD positive and culture negative, and 1 w as MTD negative and culture positive. This results in a sensitivity of 98.4%, a specificity of 98.9%, and positive and negative predictive v alues of 93.8 and 99.7%, respectively, Repeatedly, clinicians asked to test specimens of nonpulmonary origin by MTD, Although, MTD is not ap proved for use with nonrespiratory specimens, the following results we re shown, Sixty-one pleural exudate specimens showed disappointing res ults (sensitivity, 20%), However, MTD performed well with another 77 n onrespiratory specimens; 17 samples were positive and 57 samples were negative by both MTD and culture, No false-negative results were found by MTD, Three MTD-positive, culture-negative specimens had high sampl e relative light unit/cutoff relative light unit ratios, strongly sugg esting true tuberculosis, Positive microscopy and positive culture wit h MTD-negative results occurred 12 times, Those cultures showed atypic al mycobacteria 11 times and Actinomyces species once, The stability o f the reagents in the MTD kit was also assessed by testing reagents, i ncluding the enzyme mixture, kept at -70 degrees C for at least 6 mont hs, No loss of activity was seen.