Abstract: Objective To investigate the impact of plasma component preparation on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody levels the convalescent plasma from patients recovering from coronavirus disease 2019 (COVID-19) for reference to optimize the preparation method for convalescent plasma. Methods A total of 129 aliquots of blood samples donated by COVID-19 convalescents were randomly collected on January 19, 2023, and measured for the total positive rates of antibodies against IgM and IgG of SARS-CoV-2. Then each of the sample was processed into fresh plasma, cryoprecipitate-poor plasma, and virus-inactivated plasma (designated as Fresh Group, Cryoprecipitate-Poor Group, and Inactivated Group, respectively). The total positive rates of antibodies against IgM and IgG of SARS-CoV-2 were determined in the samples in the three groups after dilution at 1∶160, and the antibody level S/Co value was calculated.  Subsequently, the IgG-positive samples from the Fresh Group (after1∶160 dilution) and their corresponding samples in the Cryoprecipitate-Poor Group and Inactivated Group were further diluted to serial dilutions at 1∶160, 1∶320, 1∶640, 1∶1 280, and 1∶2 560, respectively. The S/Co values of IgG antibodies in the three groups (after1∶160 dilution) were compared under different dilution conditions. Results The total positive rates of antibodies against IgM and IgG of SARS-CoV-2 in the 129 samples were 6.98% (9/129) and 97.67% (126/129), respectively. The total IgG positive rates at 1∶160 dilution were 93.02% (120/129) in the Fresh Group, 87.60% (113/129) in the Cryoprecipitate-Poor Group, and 83.72% (108/129) in the Inactivated Group. The IgG S/Co value of the Fresh Group [8.14 (4.45, 12.24)] was higher than that of the Cryoprecipitate-Poor Group [5.92 (3.09, 10.14)], and the IgG S/Co value of the Cryoprecipitate-Poor Group was higher than that of the Inactivated Group [4.29 (1.73, 7.25)]. The difference was significant among the three groups (Z= -9.86, -9.76, -5.97, respectively; all P<0.017). In each maximum dilution gradient group, the S/Co values of IgG antibodies (after 1:160 dilution) in the fresh group samples were significantly higher than those in the Cryoprecipitate-Poor Group and the Inactivated Group. Additionally, in the maximum dilution gradient groups of  1∶320, 1∶640 and 1∶1 280 , there were statistically significant differences among the three groups of samples (all P<0.017). Conclusion The preparation process may obviously affect the IgG antibody level in the convalescent plasma from COVID-19 survivors, for which it is recommended to further optimize the plasma preparation process to maximize the retention of IgG antibody activity, thereby ensuring the quality of plasma for clinical application. 

Key words: SARS-CoV-2, Convalescent plasma, Component preparation, Antibody