Association between ABO blood groups and clinical manifestations and outcomes of COVID-19: a retrospective cross-sectional study in southeast Iran.

Blood groups significantly influence individuals' immune responses and the severity of diseases. This study examined the association between ABO blood groups and clinical features, comorbidities, and outcomes in COVID-19 patients in southeast Iran. This retrospective cross-sectional study included 894 RT-PCR-confirmed COVID-19 patients admitted to two referral hospitals in southeast Iran (April-September 2020). Medical records were reviewed for demographic data, ABO blood groups, clinical features, comorbidities, and outcomes. Disease severity was classified using NIH criteria. Chi-square, Kruskal-Wallis, and multivariable logistic regression (adjusted for age, sex, and comorbidities) were used for analysis. The mean age was 37.36 ± 14.63 years, and 53.1% were female. The mean number of symptoms varied significantly across ABO blood groups (P = 0.014), with group AB showing the lowest values. Hospitalization rates also differed (P = 0.003), being highest in group O. Significant associations were observed between blood groups and fever/chills, cough, rhinorrhea, headache, and gastrointestinal symptoms (all P < 0.05). Comorbidities were more frequent in group O (P = 0.005), particularly cardiovascular disease (P = 0.037). Blood group AB remained independently associated with fewer symptoms after adjustment (aOR = 0.68, 95% CI 0.47-0.98). ABO blood groups were associated with clinical presentation and comorbidities in COVID-19 patients. Blood group O showed higher rates of comorbidities and hospitalization, while blood group AB had a milder symptom profile.