Patient education: Coombs test (The Basics)

What is a Coombs test? — 

This is a type of blood test. There are 2 types:

●Direct Coombs test – This checks for certain antibodies that could attack red blood cells. It is also called a "direct antiglobulin test," or "DAT."

●Indirect Coombs test – Some people have antibodies that can attack red blood cells from another person. This can happen if you get a blood transfusion or if you are pregnant. This test is done with another test to find out your blood type. It is also called an "indirect antibody test," "antibody test," or "antibody screen."

Antibodies are made by the body's immune system. Normally, the immune system makes antibodies against germs like bacteria or viruses. Sometimes, antibodies can be made against healthy cells instead.

Why might I get a Coombs test? — 

Your doctor might order this test:

●To find the cause of anemia – Anemia is when you have too few red blood cells. When the body is destroying its own red blood cells, it is called "autoimmune hemolytic anemia." Hemolytic means the red blood cells are being destroyed.

●If you need to get a blood transfusion – Knowing if your blood has certain antibodies can help your doctor make sure you get donated blood that is safe for you.

●If you are pregnant – The test can show if you have antibodies that could attack your fetus's red blood cells. This information helps your doctor plan for treatment before and after birth.

How do I prepare for a Coombs test? — 

You need to get a "blood draw." Your doctor or nurse will tell you where to go for this.

It might help to wear a short-sleeve shirt to your blood draw appointment. This makes it easier for the person drawing your blood to get to your arm.

What happens during a blood draw? — 

A needle is used to take a small amount of blood from your arm (figure 1). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or have a bleeding problem – They will make sure your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Most of the time, getting blood taken does not cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — 

Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

If your Coombs test shows an antibody against red blood cells, your doctor or nurse will talk to you about what to do next:

●If you are getting a transfusion, they will make sure to give you blood that the antibodies will not react with.

●If you have anemia, they might need to do more tests to figure out the cause. The results also help them decide what treatments will work best.

If you do have a health problem, your doctor will work with you to come up with a treatment plan.

More on this topic

Patient education: Red blood cell antibody screening (The Basics)
Patient education: Blood transfusion (The Basics)
Patient education: Blood type test (The Basics)
Patient education: Autoimmune hemolytic anemia (The Basics)

Patient education: Blood donation and transfusion (Beyond the Basics)