Evaluation of Adapted Whole-Blood Interferon-γ Release Assays for the Diagnosis of Pleural Tuberculosis

Abstract

Background: Pleural tuberculosis (TB) remains difficult to diagnose despite numerous diagnostic tools. Recently, in vitro interferon (IFN)-γ-based assays have been introduced in the diagnosis of latent TB, but these techniques have not been established in the diagnosis of active TB disease, including pleural TB. Objectives: It was the aim of this study to assess the accuracy of the commercially available QuantiFERON® TB Gold assay and adapted variants of the assay, using pleural fluid or isolated pleural fluid cells for the diagnosis of pleural TB. Methods: We recruited 66 consecutive patients with a pleural effusion of unknown cause presenting at a tertiary academic health care centre in Cape Town, South Africa, a high prevalence area of TB. Blood and pleural fluid were collected at presentation for IFN-γ assays and the results evaluated for diagnostic accuracy. Results: The clinical diagnosis was TB in 30 (46%), malignancy in 20 (30%), parapneumonic effusion/empyema in 8 (12%) and effusion due to other causes in 8 patients (12%). Ex vivo pleural fluid IFN-γ levels accurately identified TB in all patients and were superior to the QuantiFERON In Tube assay using blood and pleural fluid (73 and 57% sensitivity, with 71 and 87% specificity, respectively) and the QuantiFERON Gold assay applied to isolated pleural fluid cells (100% sensitivity and 67% specificity). Conclusion: The ex vivo pleural fluid interferon-γ level is an accurate marker for the diagnosis of pleural TB, and the QuantiFERON TB Gold assay performed with peripheral blood or adapted for pleural fluid cells does not add diagnostic value.