Coombs Test

Overview

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

An indirect Coombs test is given to every pregnant person to see if they 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 (developing baby), 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 your baby. Therefore, during your first pregnancy, your baby probably wouldn’t be affected. However, if you get pregnant again with an Rh-positive baby, the existing antibodies in your blood could attack your baby’s 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, then the problem can almost always be prevented with treatment. If you’re already sensitized, then treatment can help protect your baby. 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.