Efficacy of Interferon Gamma Release Assay for Differential Diagnosis of Pulmonary Tuberculosis and Nontuberculous Mycobacterial Lung Disease

Abstract

PURPOSE: When AFB smear is positive, it is difficult to distinguish between pulmonary tuberculosis and nontuberculous mycobacterial lung disease. We assessed efficacy of interferon gamma release assay for differential diagnosis of pulmonary tuberculosis and nontuberculous mycobacterial lung disease. METHODS: We selected patients who had pulmonary tuberculosis or nontuberculous mycobacterial lung disease and received interferon gamma release assay. Pulmonary tuberculosis is defined as identification of Mycobacterium tuberculosis in sputum culture and nontuberculous mycobacterial lung disease is defined as criteria according to ATS guideline. We surveyed age, sex, height, weight, body mass index, TB history, smoking history, hypertension, diabetes mellitus, white blood cell count, hemoglobin, platelet, lymphocyte, C-reactive protein, AFB smear, AFB culture, tuberculin skin test and interferon gamma release assay. RESULTS: The age, TB history, platelet, and lymphocyte have statistical significance. In pulmonary tuberculosis, TST positive rate was 69% and QFT-GIT (QuantiFERON-TB Gold In-Tube test) positive rate was 85%. In nontuberculous mycobacterial lung disease, TST positive rate was 36.1% and QFT-GIT positive rate was 32.9%. p-value was 0.001 and <0.001 respectively. Because TB history could affect interferon gamma release assay result, we excluded nontuberculous mycobacterial lung disease patients who had TB history and reviewed the data again. In pulmonary tuberculosis, TST positive rate was 69% and QFT-GIT positive rate was 85.0%. In nontuberculous mycobacterial lung disease, TST positive rate was 36.4% and QFT-GIT positive rate is 26.1%. p-value was 0.005 and <0.001 respectively. CONCLUSIONS: In our study, interferon gamma release assay have statistical significant usefulness for differential diagnosis. However, in nontuberculous mycobacterial lung disease, QFT-GIT positive rate was 32.9%. It means that interferon gamma release assay alone can not make a differential diagnosis. We consider that potential causes are high prevalence of latent TB infection and TB history. Also our study has several limitations such as retrospective analysis, less NTM patient number, and limited coverage of TST. Therefore, when a differential diagnosis is needed, we must take interferon gamma release assay, check clinical conditions, review imaging studies, and confirm the other bacterial cultures, etc CLINICAL IMPLICATIONS: pulmonary tuberculosis, nontuberculous mycobacterial lung disease, interferon gamma release assay.