Stability of SARS-CoV-2 antibody in serum under various usage and storage conditions

Introduction: We investigated the effect of two preanalytical variables, temperature change and freezing-thawing of serum samples, on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG levels.

Methodology: Serum samples were collected from patients who had coronavirus disease 2019 (COVID-19) prior to vaccination. Six serum samples were included, two each with high positivity (HP), low positivity (LP), and a level of close-to-detection limit (CDL) for SARS-CoV-2 IgG. Each of these six samples was divided into three tubes and placed in refrigerators at 4-8 °C, -20 °C, and -70 °C; removed from the storage temperature once per day for 20 consecutive days; and assayed for SARS-CoV-2 IgG level.

Results: The coefficient of variation of all the remaining serum samples were within 95% except for CDL-1 serum at -70 °C, HP-2 serum at 4-8 °C, HP-2 serum at -20 °C, and HP-2 serum at -70 °C. The levels increased significantly when the temperature in the samples with CDL was reduced. The values in samples with LP at -20 °C and -70 °C were significantly higher than those at 4-8°C. In the case of samples with HP, the values of samples at -20 °C were higher than those in samples at 4-8 °C. There was no positive-negative change during any of the freeze-thaw cycles.

Conclusions: Antibody value in the samples at 4-8 °C remained stable throughout the 20 freeze-thaw cycles. The antibody value of the samples at -20 °C and -70 °C tended to elevate.