#blood groups

• ABO system — The major human blood group classification system (A, B, AB, and O), genetically determined by the presence or absence of specific antigens (agglutinogens) on the surface of red blood cells and antibodies (agglutinins) in the plasma. In modern medical lexicon, it functions as an invariable proper noun used to identify transfusion compatibility.
• Agglutinin — A specific antibody or protein substance present in blood plasma or immune serum, capable of inducing the process of agglutination (clumping together) of foreign cells, bacteria, erythrocytes, or antigen-bearing particles. It plays a fundamental role in blood typing and in the immune defense mechanisms of the organism.
• Agglutinogen — An antigen substance, protein or carbohydrate in nature, located on the outer surface of the erythrocyte membrane, bacteria, or other biological cells. Its structural interaction with a specific agglutinin in the plasma triggers the agglutination reaction, serving as the core biochemical element that defines blood types within the ABO and Rh systems.