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Blood Type Test

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

There is very little chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

Blood type tests are done before a person gets a blood transfusion and to check a pregnant woman's blood type. The following table shows the compatibility of blood types between blood donors and recipients.

Read the table as follows: A person who has A-negative blood can receive A-negative or O-negative blood.

Blood types that match
A person who has: Can receive:

A- blood

A-, O- blood

A+ blood

A-, A+, O-, O+ blood

B- blood

B-, O- blood

B+ blood

B-, B+, O-, O+ blood

AB- blood

AB-, O- blood

AB+ blood

AB-, AB+, A-, A+, B-, B+, O-, O+ blood

O- blood

O- blood

O+ blood

O-, O+ blood

Minor antigens (other than A, B, and Rh) on the red blood cells are also checked for a match before a blood transfusion.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Having a blood transfusion in the 3 months before the blood type test.
  • Having a bone marrow transplant.

What To Think About

  • Severe transfusion reactions are rare today because blood type is always done before a person receives a blood transfusion.
  • Blood type may be done to check the identity of birth parents. For example, in a paternity case, if the blood types of a mother and her child are checked against blood types of the possible fathers, the real father can sometimes be found by the blood type match. But blood type is more useful in proving that a man is not the father than it is in proving that he is the father. Other tests, such as a human leukocyte antigen (HLA) type, may be done. To learn more, see the topic Human Leukocyte Antigen (HLA).

WebMD Medical Reference from Healthwise

Last Updated: March 12, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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