Blood classification is based on

• A. Platelet count
• B. White blood cell count
• C. Antigens or lack there of on the surface of red blood cells
• D. Blood viscosity

Answer: (C)

Blood classification is determined by the presence or absence of specific antigens on the surface of red blood cells. These antigens define the ABO system (A, B, AB, or O) and the Rh system (positive or negative). The reason this is the basis for classification is that transfusion compatibility relies on matching these antigens between donor and recipient; antibodies in plasma will react with foreign antigens, leading to a transfusion reaction if mismatched. Platelet count and white blood cell count measure different aspects of blood health, not blood type, and viscosity describes how thick the blood is, not its antigenic makeup.