Abstract: Objective To investigate the predictive value of monocyte-to-lymphocyte ratio （MLR） combined with TB-RNA in smear-negative tuberculosis for differential diagnosis of pulmonary diseases. Methods One hundred and twenty patients with pulmonary diseases in the hospital were examined for blood cell counts and TB-RNA, among them included 65 smear-negative cases of pulmonary tuberculosis （experimental group） and 55 cases of non-tuberculosis （the control group） . The cut-off value of MLR was analyzed by ROC curve, and the sensitivity and specificity of the two markers and the combined detection for smear-negative pulmonary tuberculosis were calculated. Results Compared with non-tuberculosis patients, the number of peripheral monocytes, MLR and positive rate of TB-RNA in the sputum samples of smear-negative pulmonary tuberculosis patients were significantly increased （P<0.001）. The sensitivity and specificity of MLR in predicting smear-negative pulmonary tuberculosis were 61.5% and 67.3%, respectively. When combined with SAT-TB, the sensitivity, specificity, NPV and PPV were 76.9%, 67.3%, 71.2% and 73.5%, respectively. The combined sensitivity was notably higher than that of MLR and SAT-TB alone （P=0.043; P<0.001）. Conclusion The MLR combined with SAT-TB has a promising predictive and differential diagnostic significance in smear-negative pulmonary tuberculosis, indicating a potential value in controlling the spread of tuberculosis.

Key words: Smear-negative pulmonary tuberculosis, Isothermal amplification, Monocyte-to-lymphocyte ratio, Differential diagnosis