Comparison of QuantiFERON-TB Gold Plus results using ELISA and automated CLIA detection: a 39,000-sample real-world study

ABSTRACT QuantiFERON-TB Gold Plus (QFT-Plus) is a widely used interferon-γ release assay (IGRA) for the diagnosis of Mycobacterium tuberculosis infection. Recent advances introduced fully automated chemiluminescence immunoassay (CLIA) platforms as alternatives to conventional enzyme-linked immunosorbent assay (ELISA), potentially improving analytical performance and laboratory workflow. This study compared ELISA- and CLIA-based QFT-Plus assays using both lyophilized and liquid conjugate formulations in routine clinical practice. This retrospective study included 39,604 QFT-Plus assays performed during three distinct 1-year periods: 2019 (ELISA), 2023 (CLIA with lyophilized conjugate), and 2024 (CLIA with liquid conjugate). Test results were classified as positive, negative, or indeterminate. Indeterminate results were further categorized as due to low mitogen response (LMR) or high Nil value (HNV). Indeterminate results significantly decreased from 6.5% (777/11,885) with ELISA to 3.1% (394/12,690) with CLIA test using lyophilized conjugate and 3.1% (470/15,029) of CLIA tests using the liquid conjugate ( P < 0.0001). Positive results accounted for 10.6 (1,254/11,885), 10.3 (1,312/12,690), and 9.0% (1,355/15,029) of tests, respectively. Among indeterminate results, LMR accounted for 97.3% (756/777) with ELISA, whereas HNV accounted for 27.4 (108/394) and 16.8% (79/470) with the lyophilized- and liquid-conjugate CLIA methods, respectively. Agreement between TB1 and TB2 responses was consistently high across all methods (98.5–98.8%; κ = 0.92). CLIA-based QFT-Plus assays were significantly associated with a lower proportion of indeterminate results while maintaining an excellent TB1/TB2 concordance compared with ELISA. These findings support fully automated CLIA platforms as a robust and efficient alternative to conventional ELISA for high-throughput tuberculosis screening and routine clinical diagnostics. IMPORTANCE This study provides a large real-world evaluation of QuantiFERON-TB Gold Plus testing across different analytical platforms, including more than 39,000 tests performed in routine clinical practice. The transition from conventional enzyme-linked immunosorbent assay (ELISA) to automated chemiluminescence immunoassay (CLIA) was associated with an approximately 50% decrease in indeterminate results from 6.5 to 3.1%, with similarly low rates observed using both lyophilized and liquid conjugate formulations. Beyond documenting this substantial reduction, our study reveals a marked difference in the causes of indeterminate results: low mitogen response predominated with ELISA, whereas high Nil values accounted for a larger proportion of indeterminate results with CLIA. These findings, interpreted together with our previous paired-sample comparison, indicate that differences in quantitative IFN-γ measurement across platforms may affect how samples are classified against fixed decision thresholds.