Antibody Tests (Coombs Test)
Why It Is Done
Direct Coombs test
The direct Coombs test finds antibodies attached to your red blood cells. The antibodies may be those your body made because of disease or those you get in a blood transfusion.
The direct Coombs test also may be done on a newborn baby with Rh-positive blood whose mother has Rh-negative blood. The test shows whether the mother has made antibodies and if the antibodies have moved through the placenta to her baby.
Indirect Coombs test
The indirect Coombs test finds certain antibodies that are in the liquid part of your blood (serum). These antibodies can attack red blood cells but are not attached to your red blood cells. The indirect Coombs test is commonly done to find antibodies in a recipient's or donor's blood before a transfusion.
A test to determine whether a woman has Rh-positive or Rh-negative blood (Rh antibody titer) is done early in pregnancy. If she is Rh-negative, steps can be taken to protect the baby.
How To Prepare
You do not need to do anything before you have this test.
How It Is Done
The health professional drawing blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. If the needle is not placed correctly or if the vein collapses, more than one needle stick may be needed.
- Hook a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure to the site and then a bandage.
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.