Coombs Test

What is a Coombs test?

A Coombs test checks for antibodies that can attack your red blood cells. Antibodies are a vital part of your immune system. They fight off antigens (like bacteria, viruses and other toxins) to keep you healthy. But sometimes antibodies mistakenly attack normal, healthy cells instead.

What is the Coombs test used for?

First, it’s important to note that there are two different types of Coombs tests: direct and indirect.

• Direct Coombs test (sometimes called a direct antiglobulin test) looks at your red blood cells to see if there are antibodies attached to them. It’s often used to diagnose blood-related conditions such as autoimmune hemolytic anemia. People with autoimmune hemolytic anemia don’t have enough red blood cells because their body destroys them too soon.
• Indirect Coombs test tells your provider if there are antibodies present in your bloodstream that could attach to red blood cells. It’s used as a screening process to see how you’ll react to a blood transfusion. An indirect Coombs test is also routinely given as part of prenatal testing.

Coombs test during pregnancy

Your provider will give you an indirect Coombs test if you're pregnant to see if you have antibodies against Rh-positive blood. For example, if you have an Rh-negative blood type (such as O-, A-, B- or AB-), your red blood cells don’t have the Rh factor marker on them. But people with Rh-positive blood types do have this specific marker.

If an Rh-negative person is pregnant with an Rh-positive fetus, then Rh sensitization can occur. This means that your immune system will mistakenly target the Rh factor as a threat and make antibodies to destroy it. It can take a long time for your body to create antibodies that could harm the fetus. Therefore, during your first pregnancy, the fetus probably wouldn’t be affected. However, if you get pregnant again with an Rh-positive fetus, the existing antibodies in your blood could attack its red blood cells. This can result in Rh disease, which is characterized by anemia, jaundice or other serious health problems. These medical issues usually worsen with every Rh-positive pregnancy you have.

If you’re at risk for Rh sensitization, treatment can almost always prevent this problem. If you’re already sensitized, then treatment can help protect the fetus. That’s why it’s so important to perform the Coombs test during your first trimester.

Coombs test for newborn babies

If your baby is born with jaundice, then your healthcare provider will likely perform a Coombs test. This helps detect any “foreign” antibodies that have attached to your newborn’s red blood cells.

How does the Coombs test work?

To perform the Coombs test, your healthcare provider will need to take a small sample of your blood.

How do I prepare for a Coombs test?

No preparation is necessary before a Coombs test.

What can I expect during the test?

Your healthcare provider uses a small needle to take a sample of blood from a vein in your arm or hand. You may feel a slight “pinch” or “prick” on your skin when the needle goes in. Once the sample is collected, it’s sent to a lab for analysis. Your provider will put a bandage over the location where the needle was placed. You can remove the bandage after 10 to 20 minutes.

When should I know the results of the test?

In most cases, you’ll find out the results of your test within 24 hours.

What does a positive Coombs test mean?

A positive (abnormal) Coombs test means that you have antibodies that can attack your red blood cells. This can be caused by several conditions, including:

• Autoimmune hemolytic anemia.
• Infectious mononucleosis.
• Chronic lymphocytic leukemia.
• Syphilis.
• Mycoplasma infection, a type of respiratory illness.
• Lupus.
• A negative reaction to a blood transfusion.

What does a positive test before a blood transfusion mean?

If you test positive before a blood transfusion, it means that your healthcare provider needs to use caution when choosing a donor. People who receive a lot of blood transfusions usually develop several different antibodies. As a result, they may have trouble finding blood that will work.

What does a positive test during pregnancy mean?

If you test positive during your pregnancy, it means you’ll need to take steps to protect the fetus from Rh sensitization.

What does Coombs positive mean for a baby?

Generally, a positive Coombs test result indicates anemia or jaundice. If the fetus tests positive, then your healthcare provider will perform an examination and recommend appropriate treatment.

What does a negative Coombs test result mean?

A negative (normal) test result is good news. It means that no antibodies attached to red blood cells were found. Depending on your situation, it means that you:

• Can safely receive blood from a donor during a transfusion.
• Don’t have to worry about Rh sensitization affecting the fetus.

When should I call my healthcare provider?

If you develop symptoms of hemolytic anemia, such as jaundice, weakness, dizziness or confusion, call your healthcare provider right away. They can perform an examination and run tests to determine the appropriate treatment.

Many common warning signs can overlap with symptoms of other diseases and conditions. If you notice that something isn’t quite right, schedule an appointment with your provider.