BACKGROUND: Tuberculous pleural effusion (TPE) is the most common extrapulmonary manifestation which still has lasting effect on lung function, however conventional diagnostic tests for TPE register multiple limitations.
OBJECTIVES: This study aims to investigate diagnostic efficacy of the interferon gamma release assay (IGRA: T-SPOT.TB) in TPE patients of different characteristics comparing to adenosine deaminase (ADA), in order to clarify its appropriate setting in clinical diagnosis.
METHODS: We performed a prospective, single-centre study including all suspected pleural effusion patients consecutively from June 2015 to October 2018. By using receiver operating characteristic (ROC) curves, technical cut-offs for all enrolled participants were determined, and the utility of IGRA for pleural fluid (PF) was analysed. We obtained the independent risk factors using logistic regression analysis for TPE and evaluated the performance of the T-SPOT assay stratified by risk factors in comparison to ADA.
RESULTS: A total of 601 individuals was consecutively recruited. The maximum of early secretory antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) in the PF T-SPOT assay had the best diagnostic efficiency in our study, with a sensitivity of 83.0% and a specificity of 83.1%. The corresponding cut-off value was 466 SFCs/106 mononuclear cells, which was equal to ADA (0.885 vs 0.887, P=0.957) and superior to PB. Among the TPE patients with low ADA (<40 IU/L), the sensitivity and specificity of PF T-SPOT were still 87.9% and 90.5%, respectively. The utility of ADA was negatively related to increasing age, but the PF T-SPOT test had a steady performance at all ages. Age (<45 yrs; odds ratio (OR) = 5.61, 95% confidence interval (CI) 3.59-8.78; P<0.001), gender (male; OR = 2.68, 95% CI 1.75-2.88; P<0.001) and body mass index (BMI) (<22; OR = 1.93, 95% CI 1.30-2.88; P=0.001) were independently associated with the risk of TB by multivariate logistic regression analysis. Notably, when stratified by risk factor, the sensitivity of PF T-SPOT was superior to the sensitivity (76.5% vs. 23.5%, P=0.016) for ADA and had noninferior specificity (84.4% vs. 96.9%, P=0.370).
CONCLUSIONS: In conclusion, the overall potency of the PF T-SPOT assay is equal to that of ADA for diagnosing TPE. In addition, the PF T-SPOT assay can effectively discriminate TPE patients whose ADA is lower than 40 IU/L and is extremely superior to ADA in unconventional TPE patients (age≥45 yrs, female or BMI≥22). The PF T-SPOT assay is an excellent choice to supplement ADA to diagnose TPE.