THE APPLICATION VALUE OF TB-IGRA AND TB-AB IN THE DIFFERENTIAL DIAGNOSIS OF PULMONARY TUBERCULOSIS

Xiang Shi, Hongyun Yin, Wei Sha^* 

Department of Tuberculosis, Shanghai Pulmonary Hospital, Tongji University School of Medicine, Shanghai Clinical Research Center for infectious disease, tuberculosis, Shanghai 200433, PR China

Objective: To analyze the application value of a whole blood γ-interferon release test (TB-IGRA) and a tuberculosis antibody test (TB-Ab) in the differential diagnosis of pulmonary tuberculosis. 

Methods: A total of 167 patients admitted to our hospital from January 2019 to January 2020 were divided into the tuberculosis group (n=80) and the pneumonia group (n=87) according to the pathological examination of the patients. All patients underwent TB-IGRA and TB-Ab examinations within 24 hours of admission. Next, the negative–positive ratios of TB-IGRA, TB-Ab, and sputum specimens in each group were compared. The possible risk factors of TB-IGRA and TB-Ab test false positives were analyzed, and the diagnostic values of TB-IGRA and TB-Ab alone and in combination in the differential diagnoses of tuberculosis were analyzed using an ROC curve.

Results: Compared with the pathological results, the positive rate of TB-IGRA for identifying tuberculosis was 91.25%, the negative rate was 8.75%. In addition, the positive rate for identifying pneumonia was 21.84%, and the negative rate was 78.16%. The positive rate of TB-IGRA for identifying tuberculosis was 86.25%, and the negative rate was 13.75%. The positive rate for identifying pneumonia was 28.74%, and the negative rate was 71.26%. The positive rate of sputum smears for identifying tuberculosis was 22.50%, and the negative rate was 77.50%. The positive rate for identifying pneumonia was 2.30%, and the negative rate was 97.70%. Among the 83 tuberculosis patients, 73 were true positives of TB-IGRA, and seven were false negatives. Analysis of the factors that may cause false negatives of TB-IGRA showed that age (≥65 years) and lymphocyte decrease (<1.1×109), WBC (>9.5×109), absolute value of neutrophils (>6.3×109), CRP (>100mg/l), tumors, diabetes, pleural effusion, and fever were not factors leading to false negatives (P>0.05). The ROC curve analysis showed that the AUC of TB-IGRA in the differential diagnosis of tuberculosis was 0.847, the sensitivity was 92.65%, and the specificity was 85.16%. Furthermore, the AUC of TB-AB in the differential diagnosis of tuberculosis was 0.788, the sensitivity was 85.26%, and the specificity was 72.24%. The AUC of the two parallel tests to diagnose and differentiate tuberculosis was 0.757, the sensitivity was 95.00%, and the specificity was 54.02%. The AUC of the two systems to diagnose and differentiate tuberculosis was 0.878, the sensitivity was 82.50%, and the specificity was 93.10%. 

Conclusion: Compared with the pathological results, TB-IGRA and TB-Ab have higher positive rates in the diagnoses of pulmonary tuberculosis. Among them, age, lymphocyte reduction, infection status, tumor, diabetes, and their complications are not factors causing TB-IGRA false negatives, which is better than TB-Ab, which can be widely used in a clinical setting.