Retrospective Analysis of Coronavirus SARS-CoV-2 Antibody Levels in COVID-19 Convalescent Plasma From Blood Donors.

Objective: To detect and analyze coronavirus SARS-CoV-2 antibody levels in convalescent plasma from donors who have recovered from COVID-19. Methods: Plasma samples from 88 donors aged 20-54 years who were diagnosed with COVID-19 and who were eligible to donate from Zhejiang Province, China, were collected as the experimental group, and 56 samples from healthy blood donors were used as controls. Anti-SARS-CoV-2 antibodies, including Ab and IgM, were detected via chemiluminescent immunoassay, and neutralizing antibodies were measured via the microneutralization method. Results: The positive rates of total and IgM antibodies against SARS-CoV-2 were 97.7% (86/88) and 52.3% (46/88), respectively, in the plasma samples of 88 patients who recovered from COVID-19. After 160 and 320 dilutions of the total antibody-positive samples, the positive rates were 61.6% (53/86) and 39.5% (34/86), respectively. The titer of neutralizing antibodies was 16-256 in 53 SARS-CoV-2-positive samples after 160-fold dilution of total antibodies. The titer of neutralizing antibody was 48-256 in 34 samples that were still positive after 320-fold dilution of total antibody. Among the 88 samples, 86 had titers > 4, and 10 had high titers > 80. In 2 patients with neutralizing antibody titers < 4, SARS-CoV-2 total antibody and IgM antibodies were negative. The correlation coefficient between total antibody strength and neutralizing antibody titer was 0.5198 (high correlation). The total antibody and IgM antibodies of 56 healthy blood donors were negative. Conclusions: There are individual differences in plasma antibody titers among convalescent patients. Antibody detection is helpful for screening out plasma with high antibody titers for the treatment of patients with severe disease.