Evaluation of diagnostic agreement between STANDARD E TB-Feron ELISA and TB-Feron FIA for tuberculosis infection in prison settings in Paraguay

Introduction Accurate diagnosis of tuberculosis (TB) infection is essential for TB control, particularly in high-risk populations. Interferon-gamma release assays (IGRAs) are widely used for TB infection screening. This study assesses the diagnostic agreement between the STANDARD™ F TB-Feron fluorescence immunoassay (FIA) and the WHO-approved STANDARD E TB-Feron ELISA in penitentiary settings in Paraguay. Methods A cross-sectional study was conducted among 737 participants (642 incarcerated individuals and 95 staff members). Both assays were performed on the same blood samples from each participant. Agreement was assessed using the Kappa coefficient, with stratified analyses across predefined risk groups: G1, no known TB exposure ( n = 71); G2, TB exposure ( n = 525); G3, active TB ( n = 67); and G4, previously treated and cured TB ( n = 74). Results Overall positivity was 57.7% with FIA and 56.9% with ELISA. Positivity rates for FIA/ELISA were: G1 (22.9%/22.9%), G2 (57.7%/58.4%), G3 (79.1%/79.1%), and G4 (71.6%/71.6%). Overall agreement was excellent (κ = 0.851; 95% CI: 0.812–0.889; p < 0.0001). Stratified analyses showed moderate agreement in G1 (κ = 0.595) and excellent agreement in the remaining groups. Conclusion The STANDARD F TB-Feron FIA demonstrated excellent concordance with ELISA, supporting its use as a reliable alternative for TB infection screening. In addition, the FIA offers key operational advantages, including reduced hands-on time (approximately 15 min compared with several hours for ELISA), the ability to process single samples without batch runs, and the use of portable equipment requiring less laboratory infrastructure, making it particularly suitable for decentralized and resource-limited settings.