Evaluation of the Upgraded Amplified Mycobacterium Tuberculosis Direct Test (Gen-Probe) for direct detection of Mycobacterium tuberculosis in respiratory and non-respiratory specimens

We evaluated the upgraded Amplified Mycobacterium Tuberculosis Direct Test kit (AMTD) (Gen-Probe Inc.) for the direct detection of Mycobacterium tuber culosis in respiratory and non-respiratory specimens, and compared the resu lts between the traditional 30,000 RLUs cutoff criteria (C) and three equiv ocal ranges (30,000-100,000, RI; 30,000-500,000, R2; and 30,000-1,000,000, R3). We tested 663 respiratory and 238 non-respirator), samples from 464 pa tients. The gold standard was considered to be the combination of culture a nd clinical data. One hundred and nineteen samples were from 56 patients wi th pulmonary tuberculosis, and 36 samples were from 19 patients with extrap ulmonary tuberculosis. When C criteria was applied, the sensitivity and spe cificity values were 90.8 and 93.0% for respiratory specimens, while they w ere 88.9 and 92.1% for non-respiratory specimens (p = NS). The sensitivity was significantly higher in smear-positive specimens (96.7%) than in smear- negative ones (81.0%) (p < 0.05). When compared with C criteria, the overal l sensitivity was maintained at 90.3% for R1 criteria, and slightly decreas ed to 89.7% for R2 and R3 criteria (p = NS). Overall, specificity increased significantly from 92.9% (C) to 97.5% (R1), 99.1% (R2), and 99.2% (R3). Ap plication of R2 or R3 criteria improved significantly the specificity of th e test with little decrease in sensitivity. (C) 2001 Elsevier Science Inc. All rights reserved.