Abstract:

Objective To evaluate the diagnostic ability of Mycobacterium tuberculosis by acid-fast staining microscopy (smear), solid culture of L-J medium (L-J), liquid culture of BACTEC MGIT 960 (MGIT 960) and GeneXpert MTB/RIF (GeneXpert).Methods Sputum specimens from 451 suspected tuberculosis patients were collected from January 1, 2018 to December 31, 2018. Meanwhile, 4 testing methods including smear, L-J, MGIT 960 and GeneXpert were used for detection. The results of the 4 testing methods were based on the clinical diagnosis (generally divided into “tuberculosis patients” and “non-tuberculosis patients”), and the sensitivity, specificity, positive predictive value, negative predictive value and consistency of the 4 testing methods were calculated. The positive rate of the combined examination of the 4 testing methods was also calculated(one positive of any testing method was considered combined positive).Results The final clinical diagnosis was based on the criteria WS 288-2017, among 451 suspected tuberculosis patients, 227 tuberculosis patients (225 tuberculosis patients, 2 tuberculosis and tuberculous pleurisy), 224 non-tuberculosis patients (11 non-tuberculous mycobacterium (NTM) pulmonary disease, 6 old pulmonary tuberculosis patients, 181 lung shadows to be checked, 3 pleural effusion patients, 1 pulmonary fibrosis patient, 3 pneumonia patients, 1 lung cancer patient, 18 close contact screening patients). The sensitivity of smear, L-J, GeneXpert and MGIT 960 was 22.5% (51/227), 32.2% (73/227), 37.9% (86/227) and 43.2% (98/227), respectively. The specificity was 96.0% (215/224), 96.4% (216/224), 100.0% (224/224), 95.1% (213/224), respectively. The consistency rate was 59.0% (266/451), 64.1% (289/451), 68.7% (310/451) and 69.0% (311/451), respectively. The sensitivity of smear and L-J combination, smear, L-J and GeneXpert combination, 4 testing methods combination was 34.8% (79/227), 43.6% (99/227), 49.8% (113/227), respectively. The specificity was 96.0% (215/224), 96.0% (215/224), 93.8% (210/224), and the consistency rate was 65.2%(294/451), 69.6%(314/451), 71.6%(323/451), respectively.Conclusion Based on the clinical diagnosis as the reference standard, the sensitivity of MGIT 960 is the highest, the specificity of GeneXpert is the highest, and the 4 testing methods combination can significantly improve the sensitivity and the consistency rate with clinical diagnosis.

Key words: Mycobacterium tuberculosis, Laboratory techniques and procedures, Diagnostic self evaluation, Evaluation studies