Cross matching
Key points
- Blood typing is a test to classify blood by determining the absence or presence of antigens on the red blood cells and the presence or absence of antibodies to these antigens in the serum.
- Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand.
- Infants and young children: The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust.
- When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation.
Alternative names
Blood typing; Rh typing; ABO blood typing
Definition
Blood typing is a test to classify blood by determining the absence or presence of antigens on the red blood cells and the presence or absence of antibodies to these antigens in the serum.
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.
How to prepare for the test
No special preparation is necessary for this test.
Infants and young children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a bruise may develop at the site where the needle was inserted. These symptoms are temporary.
Why the test is performed
While the general physical makeup of all people is the same, each individual is unique. Every person has identifiers on cells that allow the body to know that those cells belong to the individual. A and B markers are common and important identifiers. The O blood type designates the absence of the A and B markers. Another surface identifier, or antigen, on red blood cells is the Rh factor. Whether or not this antigen is present determines your blood as Rh+ (positive) or Rh- (negative).
Written and revised by
David Cohen, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
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