Impact of delayed blood donation sample processing and testing on SARS ‐ CoV ‐2 serological assay results in an evolving pandemic response

BACKGROUND: The two largest US blood collection organizations led a multiphased, multicenter nationwide SARS-CoV-2 blood donor-based serosurveillance program. The potential impact of delayed sample processing and prolonged refrigerated or frozen storage on anti-SARS-CoV-2 antibody detection was investigated. METHODS: Anti-spike (S) IgG and anti-nucleocapsid (N) total immunoglobulin levels were compared for 20 paired plasma/serum samples tested fresh and frozen after separation from cellular components on Day 5 or after ≤40 days of 4°C storage; 10 paired plasma/serum samples separated on Day 5 and tested immediately or after ≤67 days of 4°C storage; and 85 plasma and 950 serum samples tested fresh on Day 1 and after ≤209 days of -20°C storage post-separation. Proportional Bland-Altman analyses were used to estimate average bias and 95% limits of agreement (LOA). RESULTS: Antibody reactivity was stable over time regardless of serum or plasma processing delays or prolonged refrigerated or frozen storage. Bland-Altman analyses suggest only minor deviations for anti-S antibodies for samples separated within 5 days and tested frozen compared to fresh (bias: 4.23%, 95% LOA: -10.02; 18.47), after ≤40 days of storage at 4°C pre-separation (9.51%, [-73.20; 92.22]) and after ≤67 days at 4°C post-separation (-14.04%, [-28.12; 0.04]). Similar observations were obtained for anti-N antibodies including samples retested after ≤209 days of storage at -20°C (-20.3%, [-81; 40.5]). CONCLUSION: Despite challenges encountered in sample access and processing during a rapidly evolving pandemic, sample processing variability and testing delays minimally impacted serologic results and thus provide evidence for the validity of results in studies requiring variable sample handling conditions.