Objective: The present study investigates the seroconversion time course of the IgG antibody against SARS-CoV-2 and ascertains whether its levels change according to the patient’s ABO blood group. Method: A total of 36,003-convalescent plasma (CP) donations of 12,315 Turkish Red Crescent CP donors were analyzed. The ABO blood group of the CP donors was determined by Gel Centrifugation; and IgG was measured using the Euroimmun anti-SARS-CoV-2 ELISA. The differences in the distributions of mean IgG ratios among the different ABO blood groups were analyzed with One-Way ANOVA and Independent Samples T-test. Results: Among the CP donors, 98.4% were male. An antibody response to SARS-CoV-2 was noted-although in a few CP donors- on the 244th day, and a significant association between the ABO blood groups and the mean IgG ratios was noted (p: 0.001). The highest (mean±SD) antibody level was observed in the AB blood group (39.5±15.7), followed by the B (37.9±11.5) and the A blood groups (36.6±10.7), while the lowest value was recorded in the O blood group (34.4±11.5). Significant differences between all paired groups were noted in pairwise comparisons. The Rh (-) blood group (37.4±13.6) had a significantly higher antibody level than the Rh (+) blood group (36.3±11.2) (p: 0.005). Conclusion: An antibody response to SARS-CoV-2 was noted in a CP donor on the 244th day. The average IgG ratios were higher in the CP donors with the AB blood group, but lower in the O blood group. These results may be considered a valuable indication of the effectiveness of CP therapy used for the treatment of COVID-19 patients with clinically relevant blood types.

Background/aim: This study aims to comprehensively analyze the distribution of ABO and Rh blood groups, as well as demographic characteristics and regional variations, using data from 9.5 million blood donors across Türkiye. Materials and methods: In this multicenter, retrospective, cross-sectional study, data were collected from 9,587,592 healthy, voluntary donors who donated to the Turkish Red Crescent between 1998 and 2021. Donors met the criteria of being 18–70 years old, weighing over 50 kg, with hemoglobin levels above 13.5 g/dL for male and 12.5 g/dL for female. The data were evaluated based on age, gender, education level, and geographic region. Results: The ABO blood group distribution was determined as follows: A (42.1%), O (34.0%), B (16.4%), and AB (7.5%). When analyzed together with the Rh factor, A Rh+ was the most common (37.1%), while AB Rh– was the least common (0.9%). Regional analyses showed that A Rh+ was highest in the Black Sea region, whereas the Aegean region had a notably high AB Rh+ rate. The Marmara region had the highest total number of donors, while Eastern Anatolia exhibited the highest donation rate relative to its population. Demographically, 82.0% of donors were male; the 18–34 age group represented the most active segment (50.5%), and high school graduates had the highest donation rate (31.2%). Conclusion: This study provides a detailed profile of Türkiye’s blood donors, filling a gap in national blood group data. The findings support optimizing transfusion services, improving blood supply management, and refining donor recruitment strategies. Regional and demographic disparities highlight the need for targeted awareness campaigns. Addressing gender imbalances and increasing participation from underrepresented groups can enhance sustainability. Additionally, these findings contribute valuable data for clinical applications, epidemiological studies, and future healthcare policy development.