Background
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody testing is an important tool in assessment of pandemic progress, contact tracing, and identification of recovered coronavirus disease 2019 (COVID-19) patients. We evaluated an orthogonal testing algorithm (OTA) to improve test specificity in these use cases.
Conclusion
Our results show that an OTA can be used to identify patients who require further follow-up due to potential SARS CoV-2 IgG false positive results. In addition, serological testing may not be sufficiently sensitive to reliably detect prior COVID-19 infection.
Methods
A two-step OTA was applied where individuals who initially tested positive were tested with a second test. The first-line test, detecting IgG antibodies to the viral nucleocapsid protein, was validated in 130 samples and the second-line test, detecting IgG antibodies to the viral spike protein in 148 samples. The OTA was evaluated in 4333 clinical patient specimens. The seropositivity rates relative to the SARS-CoV-2 PCR positivity rates were evaluated from our entire patient population data (n = 5102).
Results
The first-line test resulted in a clinical sensitivity of 96.4% (95% CI; 82.3% to 99.4%), and specificity of 99.0% (95% CI; 94.7% to 99.8%), whereas the second-line test had a sensitivity of 100% (95% CI; 87.1% to 100%) and specificity of 98.4% (95% CI; 94.2% to 99.5%). Using the OTA, 78/98 (80%) of initially positive SARS-CoV-2 IgG results were confirmed with a second-line test, while 11/42 (26%) of previously diagnosed COVID-19 patients had no detectable antibodies as long as 94 days post PCR diagnosis.