Blood typing

What Is Blood Typing?

Blood typing is a laboratory test that determines an individual’s blood type–A, B, AB, or O. It helps ensure safe blood transfusions and is often performed before surgery.

Preparation for Blood Typing

No special preparation is needed for a blood typing test. To obtain the sample, your doctor will typically take a blood sample from a vein in your arm.


To test a sample of blood, a doctor will use a sterile needle to draw blood from the patient’s vein. The sample is then placed on a labeled slide or test tube and sent to a laboratory. The laboratory technician will examine the sample under a microscope to identify the major blood type, as well as any additional blood-typing markers. The sample will also be tested for antibodies—substances that can cause a reaction if a transfusion were to occur.


There are four major blood types: A, B, AB, and O. Additionally, each of these types can also have a positive or negative Rh factor. For example, if you are type A, it could also be type A positive or type A negative depending on if your blood contains the Rh factor. Blood types are determined by the kinds of antigens (proteins) found on the surface of your red blood cells.


Blood typing is a simple and safe procedure. As with any blood test, there is a small risk that the needle used to draw the blood sample could cause minor bleeding or mild discomfort.

Why Is Blood Typing Important?

Blood typing is important because it helps ensure safe blood transfusions. When a person receives blood from a donor with a different type, the body recognizes antigens that are not supposed to be there and can react against the foreign blood, causing a dangerous and potentially life-threatening immune reaction.

When Is Blood Typing Used?

Blood typing is often used before surgery to make sure the patient will safely accept a transfusion from a donor. Blood typing might also be used before organ transplants, pregnancy, or if an individual has an unusual antibody in their blood.