Evaluation of four molecular methods for the diagnosis of tuberculosis in pulmonary and blood samples from immunocompromised patients

The present study analysed the concordance among four different molecular diagnostic methods for tuberculosis (TB) in pulmonary and blood samples from immunocompromised patients. A total of 165 blood and 194 sputum samples were collected from 181 human immunodeficiency virus (HIV)-infected patients with upper respiratory complaints, regardless of suspicious for TB. The samples were submitted for smear microscopy, culture and molecular tests: a laboratory-developed conventional polymerase chain reaction (PCR) and real-time quantitative PCR (qPCR) and the Gen-Probe and Detect-TB Ampligenix kits. The samples were handled blindly by all the technicians involved, from sample processing to results analysis. For sputum, the sensitivity and specificity were 100% and 96.7% for qPCR, 81.8% and 94.5% for Gen-Probe and 100% and 66.3% for Detect-TB, respectively. qPCR presented the best concordance with sputum culture [kappa (k) = 0.864)], followed by Gen-Probe (k = 0.682). For blood samples, qPCR showed 100% sensitivity and 92.3% specificity, with a substantial correlation with sputum culture (k = 0.754) and with the qPCR results obtained from sputum of the corresponding patient (k = 0.630). Conventional PCR demonstrated the worst results for sputa and blood, with a sensitivity of 100% vs. 88.9% and a specificity of 46.3% vs. 32%, respectively. Commercial or laboratory-developed molecular assays can overcome the difficulties in the diagnosis of TB in paucibacillary patients using conventional methods available in most laboratories.

Clinical Performance of the Amplified Mycobacterium tuberculosis Direct Test for the Detection of Mycobacterium tuberculosis in Non-respiratory Specimens / 대한임상병리학회지

BACKGROUND: The Amplified Mycobacterium tuberculosis Direct Test (AMTDT) has been developed for the direct detection of M. tuberculosis complex in respiratory specimens. Traditional methods for diagnosis of extrapulmonary tuberculosis such as the acid-fast bacilli (AFB) stain have their well-known limitations. We investigated the usefulness of the AMTDT for a wide range of non-respiratory specimens to establish early diagnosis of extrapulmonary tuberculosis. METHODS: 346 specimens (219 urine, 117 pleural fluid, 6 ascitic fluid, 2 lymph node, 1 gastric aspirate, and 1 pus specimens) from 340 patients referred from November 1997 to September 1998 were tested by the AMTDT. The AMTDT results were evaluated by comparing with clinical diagnosis and smear results. RESULTS: The overall sensitivity, specificity, and positive and negative predictive values of the AMTDT were 82.9%, 93.8%, 64.2%, and 97.6%, respectively. There were no difference in sensitivity and specificity between pleural fluid and urine specimens. In 31 specimens from tuberculosis patients concurrently tested with AMTDT and stain, 15 were only AMTDT positive and 4 were only stain positive. Among the results considered to be false positive, 47.2% of cases were shown as being less than 150,000 relative light units (RLU). In 30 specimens from tuberculosis patients during or after treatment, all six of the patients with reactivation or aggravation were AMTDT positive, and one case was considered to be false positive. CONCLUSIONS: Our study demonstrates the efficacy of the AMTDT in diagnosing extrapulmonary tuberculosis. Prudent interpretation of the AMTDT's results is recommended in case of that being less than 150,000 RLU.