Introduction: A group of metabolic diseases with a hyperglycemic phenotype known as diabetes mellitus impact both industrialized and developing nations. It is brought on by deviations in insulin synthesis, action, or both.
 Research Objective: This study seeks to associate the interaction of red cell indices and blood group in diabetic patients above 50 years of age. This is a case control study in which a convenient sample size of 100 individuals were recruited from a consenting population at a private hospital in Port Harcourt, Rivers State, 50 of whom were diabetic, and the remaining 50 were not.
 Methods: Using the automated 3-part differential hematology analyzer Sysmex KX-21N, a Full blood count (FBC) and differential was obtained using (Sysmex Corporation Kobe, Japan) Standardization, instrument calibration, and analysis of sample was achieved in line with accordance with the manufacturer's manual to determine the red cell indices and grouping of cells using the tile approach to determine the ABO Blood Groups. Blood samples were taken from the veins using a vacutainer tube and needle according to Chesbrough's instructions, and then put in EDTA anticoagulated bottles with clear labelling. These samples were transported right away using the triple packing procedure to the lab and stored until testing at 4°C. Inferential statistics utilizing the students' statistical t-test were employed to compare the results.
 Results: Blood group O, with a total of 25 (50%), had the highest prevalence of diabetes mellitus, followed by blood group A with a total of 12 subjects (24%) and blood group B with a total of 8 subjects (16%) and blood group AB came in last with a total of 5 participants (10%), respectively. In this study, blood group O predominated over blood groups A and B (47% against 25% versus 17%, respectively). The least common blood type in this study was AB (11%). When the Packed Cell Volume, Haemoglobin, Red Blood Cell, Mean Cell volume, Mean Cell Haemoglobin, Mean Cell Haemoglobin Concentration, and Red cell Distribution Width were examined between diabetic and non-diabetic participants, no statistically significant (p<0.05) difference was found.
 Conclusion: The findings of this study suggest that blood types O and AB are more prevalent in diabetics. We can deduce that a person's blood type may be a risk factor for developing this condition and may be useful in diagnosing it.