Abstract:

Objective: To evaluate the diagnostic reliability of smear-positive/Xpert-negative results as an early predictor for the presence of non-tuberculous mycobacteria (NTM) in clinical specimens. Methods: A retrospective analysis was conducted on laboratory examination data from patients newly diagnosed with pulmonary diseases at Henan Chest Hospital between January 2019 and April 2024. The dataset included cases with positive smear microscopy results and those with NTM confirmed by isolation and culture. The accuracy of smear-positive/Xpert-negative results as a predictive indicator for NTM isolation and identification was assessed. The proportion of patients diagnosed with NTM during the study period who presented smear-positive/Xpert-negative results was analyzed to evaluate the sensitivity of this predictive indicator. Additionally, the proportion of smear-positive tuberculosis patients with negative Xpert test results was examined to determine the specificity of this indicator. Results: Among the smear-positive patients included in the study, 8.22% (202/2458) exhibited negative Xpert test results during the same period. Of the 148 patients with smear-positive/Xpert-negative results and concurrent culture-based identification, 138 cases (93.24%) were confirmed as NTM through culture, demonstrating the high accuracy of smear-positive/Xpert-negative results as an early predictor for NTM in clinical specimens. When the additional criterion of a negative interferon-gamma release assay (IGRA) result was applied, the predictive accuracy increased to 100.00% (73/73). However, this refinement significantly reduced the sensitivity of the prediction to 37.61% (44/117). The sensitivity of smear-positive/Xpert-negative results in predicting the presence of NTM was 39.78% (109/274) among patients with NTM disease. Conversely, the specificity of this indicator was remarkably high at 99.56% (2256/2266) among patients with smear-positive tuberculosis. Conclusion: In patients suspected of tuberculosis, smear-positive/Xpert-negative results serve as an early and reliable predictor for the identification of NTM.

Key words: Atypical bacterial forms, Mycobacterium, Diagnosis, differential, Forecasting