Blood is typed according to the ABO blood typing system. Blood Typing is a method to determine what blood group a person has. To know what blood type you have is critical to safely donate blood or receive a blood transfusion. Your blood type is based on whether or not certain proteins, called antigens, are on your red blood cells and if you have antibodies against those antigens in your plasma. Blood typing also tests for the Rh factor, a protein present on the surface of red blood cells.
Scroll down for information on what classifies each blood type and their compatibility among other blood types.
The presence or absence of antigens determines a patient's blood type and it's compatibility among other blood types. These antigens, if foreign to the patient's body, may trigger an immune response if exposed. This happens typically through a miss-matched blood transfusion or when an Rh- mother carries a pregnancy with an Rh+ fetus. This emphasizes the importance of blood type screening.
Rh (Rhesus) Factor
Rh factor is a protein that can be found on the surface of red blood cells. If the Rh factor is present on your RBC’s when blood typing, the blood type is positive. If the Rh factor is not present, your blood type is negative. Rh negative blood is given to Rh negative patients and Rh positive blood is given to Rh positive patients.
Rh Factor in Pregnancy
Maternal blood type is tested during the first prenatal visit as standard practice. This determines whether the mother has the Rh factor or not. This is important because if a mother does not have the Rh factor (is Rh-) and her fetus does (is Rh+), they are Rh incompatible.
This is a problem when the blood from an Rh-positive fetus gets into the bloodstream of an Rh-negative mother, her body will fight it by creating anti-Rh antibodies. These antibodies can cross the placenta and work to destroy the fetus's blood. The anti-Rh antibody response from the mother can lead to complications in the pregnancy and newborn or even death of the newborn. Please check back for more on Rh factor in pregnancy.
There are eight different blood types classified by the proteins present or absent on the cell, including the A & B antigens and the Rh factor protein. Each blood type's antigens determine whether or not the patient's plasma contains antibodies against other blood types.
For example, a B+ blood type has both B antigens and the Rh factor present on the cell. Therefore, "A antigen" antibodies will be present in the patient's plasma causing the patient to attack Type A or AB blood if introduced into the patient's blood stream.
See the chart below for further review of blood types which are acceptable for donation or receiving based on the antigens present on each cell.
Blood typing is a standard practice to ensure safe delivery of blood and blood component therapy. Health care providers who perform blood component therapy pay close attention to adverse reactions during transfusions to ensure any immune response is detected and the transfusion is stopped.
Immune responses due to incompatible blood types can be life-threatening and need to be managed immediately. Click here for my post on blood, blood products, and blood component therapy. For more on transfusion administration, transfusion reactions, and management of a transfusion reaction when delivering blood or blood products through intravenous transfusion clink the links below.