Red blood cell Red blood cell Red blood cells, also known as RBCs, red cells, red blood corpuscles, haematids, erythroid cells or erythrocytes (from Greek "erythros" for "red" and "kytos" for "hollow vessel", with "-cyte" translated as "cell" in modern usage), are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O) to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the body's capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can
Packed red blood cells though it has other names and is commonly just called "negative" or "positive." Unlike the ABO antigens, a recipient will not usually react to the first incompatible transfusion because the adaptive immune system does not immediately recognize it. After an incompatible transfusion the recipient may develop an antibody to the antigen and will react to any further incompatible transfusions. This antibody is important because it is the most frequent cause of hemolytic disease of the newborn. Incompatible red blood cells are sometimes given to recipients who will never become pregnant, such as males or postmenopausal women, as long as they