Blood typing is a method to tell what type of blood you have. Blood typing is done so you can safely donate your blood or receive a blood transfusion. It is also done to see if you have a substance called Rh factor on the surface of your red blood cells.
Your blood type is based on whether or not certain proteins are on your red blood cells. These proteins are called antigens. Your blood type (or blood group) depends on what types your parents passed down to you.
Blood is often grouped according to the ABO blood typing system. The 4 major blood types are:
Cross matching; Rh typing; ABO blood typing; Blood group; Anemia - immune hemolytic blood type; ABO blood type; A blood type; AB blood type; O blood type
A blood sample is needed. The test to determine your blood group is called ABO typing. Your blood sample is mixed with antibodies against type A and B blood. Then, the sample is checked to see whether or not the blood cells stick together. If blood cells stick together, it means the blood reacted with one of the antibodies.
The second step is called back typing. The liquid part of your blood without cells (serum) is mixed with blood that is known to be type A and type B. People with type A blood have anti-B antibodies. People with type B blood have anti-A antibodies. Type O blood contains both types of antibodies.
The 2 steps above can accurately determine your blood type.
Rh typing uses a method similar to ABO typing. When blood typing is done to see if you have Rh factor on the surface of your red blood cells, the results will be one of these:
No special preparation is necessary for this test.
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Blood typing is done so you can safely receive a blood transfusion or a transplant. Your blood type must closely match the blood type of the blood you are receiving. If the blood types do not match:
The 2 ways that your blood and the donated blood may not match are:
You will be told which ABO blood type you have. It will be one of these:
You will also be told whether you have Rh-positive blood or Rh-negative blood.
Based on your results, your health care providers can determine which type of blood you can safely receive:
Type O blood can be given to anyone with any blood type. That is why people with type O blood are called universal blood donors.
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
There are many antigens besides the major ones (A, B, and Rh). Many minor ones are not routinely detected during blood typing. If they are not detected, you may still have a reaction when receiving certain types of blood, even if the A, B, and Rh antigens are matched.
A process called cross-matching followed by a Coombs test can help detect these minor antigens. It is done before transfusions, except in emergency situations.
Goodnough LT. Transfusion medicine. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 177.
Howard MR, Hamilton PJ. Blood groups and blood testing. In: Howard MR, Hamilton PJ, eds. Haematology: An Illustrated Colour Text. 4th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2013:chap 41.