Test performance evaluation of SARS-CoV-2 serological assays

Serological tests are essential for understanding SARS-CoV-2 exposure and immune responses. Prior research has shown that these tests can detect antibodies after infection, but their accuracy varies. No prior work had resolved the full range of performance across different assays and sample types. That uncertainty drove the need for a comprehensive evaluation of available tests. It was already known that antibody levels change over time after infection, but how this affects test results remained unclear. No prior work had resolved how cross-reactivity might impact test specificity. This gap motivated a study to assess the reliability of various assays. No prior work had resolved the impact of reader interpretation on lateral flow assays. This gap motivated the use of standardized scoring systems to evaluate test performance.

The aim of this study was to evaluate the performance of 10 lateral flow assays and two ELISAs for detecting anti-SARS-CoV-2 antibodies. The specific problem addressed was the variability in test accuracy and interpretation. The motivation was to inform the appropriate use of these tests in clinical and public health settings. The study focused on measuring sensitivity and specificity across different sample groups. It also aimed to compare IgM and IgG detection methods. The motivation was to assess whether combining antibody types improves detection rates. The study sought to determine the impact of reader interpretation on test results. The motivation was to establish best practices for using serological tests in real-world scenarios.

The study evaluated 10 lateral flow assays and two ELISAs for detecting anti-SARS-CoV-2 antibodies. A blinded specimen set was used, including 128 plasma or serum samples from RT-PCR-positive individuals and pre-COVID-19 controls. Two independent readers interpreted LFA results using a standardized intensity scoring system. The study compared IgM and IgG detection rates across assays. The study also assessed agreement between ELISAs and LFAs. The study measured test specificity using pre-COVID-19 specimens. The study tracked how seropositivity changed with time since symptom onset. The study evaluated the impact of weak LFA bands on test accuracy.

Among RT-PCR-positive individuals, seropositivity increased with time since symptom onset, peaking at 81.8-100.0% after 20 days. Test specificity ranged from 84.3-100.0% in pre-COVID-19 specimens. Specificity improved when weak LFA bands were considered negative, but this reduced sensitivity. IgM detection was more variable than IgG, with higher detection when combined. Agreement between ELISAs and LFAs ranged from 75.7-94.8%. No consistent cross-reactivity was observed across assays. Reader interpretation had a significant impact on LFA results. The study found that reader training is essential for reliable LFA performance.

The study showed heterogeneous performance across serological assays. Reader training is key to reliable LFA performance and can be tailored for survey goals. Informed use of serology will require evaluations covering the full spectrum of SARS-CoV-2 infections. The authors propose that well-designed studies are needed to elucidate mechanisms of protective immunity. The authors suggest that serological correlates of immunity will guide clinical and public health policies. The authors note that no consistent cross-reactivity was observed in the tested assays. The authors suggest that combining IgM and IgG detection improves test performance. The authors propose that standardized scoring systems improve test reliability.