Immunohematology is a part of hematology that studies the immune reactions between antigens present in erythrocytes (red blood cells) and antibodies in blood plasma. It is the area responsible for the determination of blood groups and the study of antibodies against erythrocytes, which are studies aimed at studying the presence of anti-erythrocyte antibodies (antibodies that bind to red blood cells) and their pathological significance. It is a special type of blood test. For the patient it only involves the withdrawal of a blood sample. Our immune system can naturally create antibodies against substances it does not consider its own as a defense mechanism. Sometimes such substances may be present in red blood cells that are foreign to our body.