Evaluation of the Fully-Automated Chemiluminescence Analyzer LIAISON XL for the Performance of the QuantiFERON-TB Gold Plus Assay in a Low-Incidence Tuberculosis Area.

Fernández-Huerta, Miguel; Moreto, Clara; Vila-Olmo, Neus; García de Cara, Erika-Inés; Basaez, María-Celeste; Santín, Miguel; Alcaide, Fernando

Diagnosis of latent tuberculosis infection (LTBI) is considered key in the control of tuberculosis. Interferon-gamma (IFN-γ) release assays, such as the QuantiFERON-TB® Gold Plus test (QFT-Plus), are now widely implemented for the in vitro diagnosis of LTBI. To date, the detection and quantification of IFN-γ has been mostly performed with semi-automated enzyme-linked immunosorbent assays (ELISAs), but several limitations currently exist. The study aims to evaluate the chemiluminescence immunoassay (CLIA) analyzer LIAISON® XL in comparison to ELISA for the performance of the QFT-Plus test. Between February and April 2020, 333 heparin blood samples from 323 adult patients were collected at a tertiary teaching hospital in Barcelona, Spain. Overall, the CLIA analyzer LIAISON® XL performed well for the detection of IFN-γ compared to the ELISA method, demonstrating substantial agreement (κ, 0.872) and great correlation between assays (r, >0.950). CLIA produced significantly higher values of IFN-γ IU/mL than the ELISA (p=0.004 for TB1 tube, and p=0.010 for TB2 tube). Many discrepant cases (8/15, 53.3%) corresponded to indeterminate results with ELISA (NIL-corrected mitogen value <0.5 IU/mL), which analyzed with the CLIA analyzer LIAISON® XL reverted to interpretable results. In conclusion, this analysis suggests that CLIA may potentially present a greater sensitivity for the identification of LTBI, especially among immunocompromised patients. Furthermore, the analytical variability reported between both ELISA and CLIA methods, especially around the standardized 0.35 IU/mL positivity threshold, suggests the need to refine the interpretative algorithm.