Assessing the performance of commercial serological tests for SARS-CoV-2 diagnosis

The emergence of the SARS-CoV-2 has triggered a global pandemic with profound implications for public health. Rapid changes in the pandemic landscape and limitations in in vitro diagnostics led to the introduction of numerous diagnostic devices with variable performance. In this study, evaluated three commercial serological assays in Brazil for detecting anti-SARS-CoV-2 antibodies. We collected 90 serum samples from SARS-CoV-2-negative blood donors and 352 from SARS-CoV-2-positive, unvaccinated patients, categorized by symptom onset. Subsequently, we assessed the diagnostic performance of three commercial enzyme immunoassays: GOLD ELISA COVID-19 IgG + IgM, Anti-SARS-CoV-2 NCP IgM ELISA, and Anti-SARS-CoV-2 NCP IgG ELISA. Our findings revealed that the GOLD ELISA COVID-19 IgG + IgM exhibited the highest sensitivity (57.7%) and diagnostic odds ratio, surpassing the manufacturer's reported sensitivity in most analyzed time frames, while maintaining exceptional specificity (98.9%). Conversely, the Anti-SARS-CoV-2 NCP IgG ELISA demonstrated lower sensitivity but aligned with independent evaluations, boasting a specificity of 100%. However, the Anti-SARS-CoV-2 NCP IgM ELISA exhibited lower sensitivity than claimed, particularly in samples collected shortly after positive RT-qPCR results. Performance improved 15-21 days after symptom onset and beyond 22 days, but in the first week, both Anti-SARS-CoV-2 NCP IgM ELISA and Anti-SARS-CoV-2 NCP IgG ELISA struggled to differentiate positive and negative samples. Our study emphasizes the need for standardized validation protocols to address discrepancies between manufacturer-claimed and actual performance. These insights provide essential information for healthcare practitioners and policymakers regarding the diagnostic capabilities of these assays in various clinical scenarios.