Nationwide Distribution of ABO and Rh Blood Group Phenotypes Among Mexican Outpatients: A Multicenter Retrospective Cross-Sectional Study

José Antonio Magaña-Lizárraga,1 Abraham García-Gil,1 Diana Yadira Calva-Espinosa,2 Yoseli Yoruby Leal-Leyva,3 Ariadna Patricia Langle-Martínez,4 Marco Antonio Luna-Ruiz-Esparza,1 Abraham Campos-Romero,1 Jonathan Alcántar-Fernández11Innovation and Research Department, Salud Digna, Culiacan, SIN, Mexico; 2Laboratory Department, Salud Digna, Culiacan, SIN, Mexico; 3National Reference Center I, Salud Digna, Culiacan, SIN, Mexico; 4National Reference Center II, Salud Digna, Tlalnepantla, MEX, MexicoCorrespondence: Jonathan Alcántar-Fernández, Innovation and Research Department, Salud Digna, Culiacan, SIN, Mexico, Tel +52 667-215-0764, Email [email protected]: This study aimed to determine the phenotypic distribution of ABO and Rh blood groups in a geographically diverse cohort of Mexican outpatients.Patients and Methods: A clinic-based, retrospective, cross-sectional study was conducted using anonymized electronic health records (EHRs) from 1,820,793 individuals aged 1 to 100 years who underwent clinically or administratively indicated ABO and Rh blood typing at Salud Digna clinics across all 32 Mexican states between January 2023 and July 2025. All ABO and Rh determinations were performed by forward typing using either the fully automated Galileo Echo immunohematology analyzer or by the conventional slide method using commercial anti-A, anti-B, and anti-D antisera. Demographic and blood group distributions were summarized using descriptive statistical methods, and sex-specific distributions were evaluated.Results: Among the 1,820,793 individuals analyzed (median age: 29 years), 1,193,587 (65.6%) were female and 627,206 (34.4%) were male. Blood group O was the most frequent ABO phenotype (65.99%), whereas group AB was the least common (1.50%). For the Rh system, 3.39% of individuals exhibited the Rh(d) phenotype. The overall phenotypic distribution was as follows: O Rh(D) (64.01%), A Rh(D) (23.24%), B Rh(D) (7.92%), O Rh(d) (1.98%), AB Rh(D) (1.43%), A Rh(d) (1.02%), B Rh(d) (0.32%), and AB Rh(d) (0.07%). Notably, the AB Rh(d) phenotype was not identified in Oaxaca. From a geographical perspective, a clear north-to-south gradient was observed, with increasing frequencies of the O Rh(D) phenotype toward the southern states, accompanied by declining trends observed for the remaining ABO and Rh phenotypes.Conclusion: Blood group O was the most frequent ABO phenotype, whereas the Rh(d) phenotype was relatively uncommon. The overall distribution patterns were largely consistent across the states. These findings provide a valuable resource for health authorities and blood services to support blood inventory management, inform region-specific donor recruitment strategies for less common blood group phenotypes, and optimize planning for blood transfusion services, organ transplantation, and maternal healthcare.Keywords: ABO blood group, Rh blood group, RhD antigen, blood groups, phenotype