Identifying predictors to gain sensitivity of nucleic acid amplification tests for Mycobacterium tuberculosis

Background: Tuberculosis (TB) remains one of the primary threatening of human health and its diagnosis remains unsatisfactory in clinic. Nucleic acid amplification tests (NAAT) showed higher sensitivity than culture for the diagnosis of pulmonary TB (PTB). However, NAAT are expensive and not easily deployable at the peripheral level. To improve the sensitivity of NAAT for the PTB diagnosis, the predictive factors that might be utilized to give the optimized choice of NAAT were investigated.Methods: A total of 1263 PTB suspects were enrolled for evaluation. The sensitivity, specificity and accuracy of Mtb detection in sputum and bronchoalveolar lavage fluid (BALF) were compared. Odds ratios and 95% confidence intervals were used to assess variables that associated with positive NAAT in sputum and BALF of PTB suspects.Results: An significantly enhanced sensitivity was observed when performed on NAAT (61.1%) compared with smear (9.0%) and culture of Mtb (47.8%). We found that erythrocyte sedimentation rate (ESR) (+), cavities (+) and IFN-γ release assay (IGRA) (+) are involved in the positivity of Mtb detection through NAAT. Moreover, those who are ESR (+), cavities (+) and IGRA (+), showed 86% diagnostic positivity of Mtb by NAAT.Conclusions: Our study suggested that combination of the results of ESR and IGRA and the presence of pulmonary cavity is helpful to predict the positivity of Mtb detection through NAAT. Those who are ESR (+), cavities (+) and IGRA (+), should perform NAAT for Mtb detection, because they are most likely to be bacteriologically confirmed as TB.