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
There is very little chance of a problem from
having 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
- 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.
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
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-, O- blood
A-, A+, O-, O+ blood
B-, O- blood
B-, B+, O-, O+ blood
AB-, O- blood
AB-, AB+, A-, A+, B-, B+, O-, O+
O-, O+ blood
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:
- Taking methyldopa,
levodopa, or some
antibiotics, such as cephalexin. These medicines may
- Having a blood
transfusion in the 3 months before the blood type test.
- Having a bone marrow
What To Think About
- Severe transfusion reactions are rare today
because blood type is always done before a person receives a blood
- 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. For more information, see the topic
Human Leukocyte Antigen (HLA).
blood tests are done on donated blood before using it. These include hepatitis,
syphilis, and human immunodeficiency (HIV). For more information, see the
Hepatitis B Virus Test,
Hepatitis C Virus Test,
Syphilis Tests, and
Human Immunodeficiency Virus (HIV) Test.