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 if the person who gave birth has Rh-negative blood. The test shows whether the person made antibodies and if the antibodies moved through the placenta to the 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 person who is pregnant has Rh-positive or Rh-negative blood (Rh antibody titer) is done early in pregnancy. If they are Rh-negative, steps can be taken to protect the baby.

How To Prepare

In general, there's nothing you have to do before this test, unless your doctor tells you to.

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

How long the test takes

The test will take a few minutes.

Watch

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.