Clinical diagnostic value of simultaneous amplification and testing for the diagnosis of sputum-scarce pulmonary tuberculosis

BACKGROUND: Since 20% of pulmonary tuberculosis (PTB) patients are asymptomatic, the early detection of PTB is a challenge particularly in sputum-scarce patients and diagnostic accuracy based solely on clinical characteristics and chest X-ray/CT scans are not always satisfactory. The AmpSure simultaneous amplification and testing method for the detection of Mycobacterium tuberculosis (SAT-TB assay) is an alternative approach to diagnose PTB. In the present study, we analyzed the usefulness of the SAT-TB assay for PTB diagnosis in sputum-scarce patients. METHODS: A total of 840 patients were prospectively enrolled for PTB diagnosis with bronchial alveolar lavage fluid (BALF) used as the samples for the SAT-TB assay. Of these, 536 had a definite diagnosis of PTB confirmed by positive microbiology culture, or clinical diagnosis of active PTB following anti-TB treatment with a favorable response. RESULTS: The SAT-TB assay showed a 76.44% agreement with the culture test. The sensitivity and specificity of the SAT-TB assay were 50.75% and 94.73%, respectively. The sensitivity of SAT-TB was significantly higher than that of BALF cultures (21.64%) (X(2) = 49.1503; P < 0.001) and smears (4.48%) (X(2) = 175.2315; P < 0.001). The specificity of SAT-TB was slightly lower than that of BALF cultures (98.25%) (X(2) = 2.0727; P = 0.150) and smears (98.25%) (X(2) = 2.0727; P = 0.150). The accuracy rates were 63.87% for SAT-TB, 44.50% for BALF cultures and 29.84% for BALF smears. CONCLUSION: The high accuracy of the SAT-TB assay indicated that active PTB is present and anti-TB treatment is strongly recommended regardless of smear and culture test results for sputum scarce active PTB suspected patients when BALF SAT-TB is positive.