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Journal of Clinical Microbiology, 10 1995, 2699-2703, Vol 33, No. 10
F Vlaspolder, P Singer and C Roggeveen
Five hundred fifty respiratory and nonrespiratory specimens from 340
patients were analyzed by comparing the Gen-Probe Amplified Mycobacterium
Tuberculosis Direct Test (MTD) with conventional culture, which was the
method of reference, for the detection of the Mycobacterium tuberculosis
complex. After resolution of discrepant results by retesting the samples
and reviewing the patients' clinical histories, a total of 60 respiratory
specimens were MTD and culture positive, 347 were MTD and culture negative,
4 were MTD positive and culture negative, and 1 was MTD negative and
culture positive. This results in a sensitivity of 98.4%, a specificity of
98.9%, and positive and negative predictive values of 93.8 and 99.7%,
respectively. Repeatedly, clinicians asked to test specimens of
nonpulmonary origin by MTD. Although, MTD is not approved for use with
nonrespiratory specimens, the following results were shown. Sixty-one
pleural exudate specimens showed disappointing results (sensitivity, 20%).
However, MTD performed well with another 77 nonrespiratory 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 sample relative light unit/cutoff relative
light unit ratios, strongly suggesting true tuberculosis. Positive
microscopy and positive culture with MTD-negative results occurred 12
times. Those cultures showed atypical mycobacteria 11 times and Actinomyces
species once. The stability of the reagents in the MTD kit was also
assessed by testing reagents, including the enzyme mixture, kept at -70
degrees C for at least 6 months. No loss of activity was seen.
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Diagnostic value of an amplification method (Gen-Probe) compared with that of culture for diagnosis of tuberculosis
Department of Medical Microbiology, Medical Center Alkmaar, The Netherlands.
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