Impact of the interferon-γ release assay and glomerular filtration rate on the estimation of active tuberculosis risk before bronchoscopic examinations: a retrospective pilot study

Background Bronchoscopic examinations are vital to diagnose pulmonary diseases. However, as coughing is triggered during and after the procedure, it is imperative to take measures against nosocomial infections, especially for airborne infections like tuberculosis (TB). The interferon-γ release assay (IGRA) has recently been established as a method to evaluate the infection status of TB. We aimed to ascertain the efficacy of IGRA and clinical findings in estimating the prevalence of active TB before bronchoscopy. Methods We obtained IGRA results from 136 inpatients using a QuantiFERON-TB Gold In-Tube test. Bronchoscopy samples were cultured in Mycobacteria Growth indicator tubes and 2% Ogawa solid medium. We evaluated the adjusted effects of multiple clinical variables on active TB status using a logistic regression model. In addition, multiple variables were converted into a decision tree to predict active TB. Results Five (3.7%) patients were diagnosed with culture-positive TB, two of whom were simultaneously diagnosed with non-small-cell lung carcinoma or small-cell lung carcinoma. The multivariate analysis suggested the probability of predicting active TB using the IGRA [odds ratio (OR), 72.7; 95% confidence interval (CI), 3.169-1668; P=0.007] and decreased estimated glomerular filtration rate (eGFR) (OR, 0.937; 95% CI, 0.882-0.996; P=0.038) in patients undergoing bronchoscopy. A decision tree validated the use of these two variables to predict active TB. Conclusions IGRA test results are useful for predicting active TB before bronchoscopy. This strategy could identify patients who require antibiotic therapy to prevent TB or who are in the active phase of TB.