What are blood type and Rh factor?

Rh factor is part of your blood type and both are part of the test known as a type and screen. If you've received lab test results showing your blood type or have lab test questions about your lab test report, understanding what the technologist looks for can be helpful. When testing your blood type, the lab technologist searches for specific antigens on your red blood cells that determine your blood type. An antigen is a molecule on the red blood cell. If your blood type is A, this means you have the A antigen on your red blood cells. If your blood type is B, this means you have the B antigen on your red blood cells. If your blood type is AB, this means you have both the A and B antigens on your red blood cells. If your blood type is O, this means you have neither the A nor the B antigen on your red blood cells.

Your blood type also consists of whether you carry the Rh factor or not. The Rh factor is characterized by the presence or absence of the D antigen on the red blood cells. If you carry the D antigen, you are considered Rh+. If you lack the D antigen on the red blood cells, you are considered Rh(-). Therefore your full blood type could be A+, A-, B+, B-, AB+, AB-, O+, or O-.

Why are blood type and Rh factor important?

The blood type and Rh are extremely important in instances where an individual requires a blood transfusion or during pregnancy. If an individual requires a transfusion, we need to make sure that they are receiving compatible blood. This means that we need to give them a transfusion with a unit of blood that matches their blood type as well as their Rh. If an individual is a type A+, they should receive A+ blood if a transfusion is needed. If an individual is a type B-, they should receive B- blood if a transfusion is needed. In emergency situations, an individual can receive type O- blood while the lab test is being done to determine blood type. Type O- is considered a universal donor because it is missing the A, B, and D antigens on the red blood cell and therefore will not cause a reaction with the recipient's body.

Rh factor and pregnancy

In instances of pregnancy, the blood type and Rh becomes important in determining whether there is an increased risk of Hemolytic Disease of the Fetus and Newborn (HDFN). HDFN occurs when mom is Rh(-) but baby is Rh(+). If baby's blood is introduced to mom, this can cause mom's body to create an antibody against the Rh factor. If mom has any subsequent pregnancies, the antibody can cross the placenta and start attacking the baby's red blood cells. This can lead to severe anemia in the fetus or newborn, which can lead to an increased level of bilirubin, respiratory distress, and heart failure in the fetus or newborn. In order to avoid this, each pregnant woman has a blood type and screen done. If the woman is Rh(+), then there is nothing further that needs to be done. If a woman is Rh(-), she will then need to receive RhoGAM during pregnancy and after delivery. RhoGAM will ensure that the woman will not develop the antibody against the Rh factor, and therefore greatly minimizes the risk of HDFN.

Why would a doctor order a type and screen?

How to prepare for a type and screen?

Blood typing is done with a simple blood draw from a vein. No fasting or special diet is required for this test. A blood draw is a simple procedure in which a needle is inserted into a vein and is used to fill a tube. The tube is then sent to the lab where the testing will take place.

Questions to ask your provider

Final takeaway

Blood type and Rh are part of a lab test known as the type and screen. Your blood type is determined by the presence or absence of certain antigens on your red blood cells. Your blood type is very important in ensuring that a safe and compatible blood transfusion takes place. A blood type is also very important in ensuring that a woman has a safe pregnancy and a fetus or newborn are born healthy.

Staring at your lab test report with lab test questions? Understanding your lab test results starts here.