[Assessment of performance of "amplified Mycobacterium tuberculosis direct test" in pulmonary and extrapulmonary...

Since rapid diagnosis is critical in control of tuberculosis, nucleic acid amplification techniques have been widely used. The purpose of the present study was to assess the performance of Amplified Mycobacterium tuberculosis Direct Test (Amplified MTD Test, Gen-Probe) for the diagnosis of pulmonary and extrapulmonary tuberculosis in our laboratory. A total of 267 specimens (170 pulmonary and 97 extrapulmonary) were tested in the Clinical Mycobacteriology Laboratory of Manisa (a province located in Aegean part of Turkey) University Hospital from September 2001 to March 2005. When Amplified MTD (AMTD) test results were compared to the culture results taken as the gold standard, the sensitivity, specificity, positive and negative predictive values (PPV, NPV) for pulmonary specimens were found to be 84%, 96%, 73%, and 98%, respectively. When AMTD test positive, culture negative discrepant results were evaluated against the clinical history of the patients, these rates were detected as; 88%, 100%, 100%, and 98%, respectively. For 97 extrapulmonary specimens, sensitivity, specificity, PPV and NPV of AMTD test were 60%, 100%, 100%, and 98%, respectively. In conclusion, the results of the AMTD assay were reliable for the rapid diagnosis of pulmonary tuberculosis; if the results were evaluated together with the clinical status of patients, the performance of the test would be increased. However, even though the culture positive extrapulmonary specimens were sparse in our study (5%), the sensitivity of the AMTD test in extrapulmonary specimens was found less than that in pulmonary specimens. Therefore it is thought that AMTD test results should be evaluated carefully for the diagnosis of extrapulmonary tuberculosis.