Does this test have other names?

Direct Coombs test

What is this test?

The direct antiglobulin test is a blood test used to diagnose a type of anemia caused by your immune system. Your immune system is your body's defense system. It makes proteins called antibodies to attack foreign invaders. In some cases, your immune system can make antibodies against red blood cells. Red blood cells carry oxygen through the blood to different parts of the body. This causes red blood cells to break down before they normally would. This condition is called hemolytic anemia.

Why do I need this test?

You may need this test to tell your healthcare provider whether you have antibodies that have attached to your red blood cells. You may need this test if you have symptoms of a reaction after a blood transfusion. A baby may need this blood test if the baby's mother makes antibodies against the baby's red blood cells and passes those antibodies to the baby inside the womb. This condition is called hemolytic disease of the newborn.

The most common cause of hemolytic anemia is when your immune system makes antibodies to your own red blood cells by mistake. When your immune system makes antibodies against your own healthy cells, it is called an autoimmune disease. Symptoms of hemolytic anemia may include:

• Tiredness

• Shortness of breath

• Headaches or dizziness

• Coldness in your hands and feet

• Yellowing of your skin, eyes, or under your tongue (jaundice)

• Dark urine

• Heart problems, such as an irregular heartbeat, heart murmur, or heart failure

• Blood tests that show low numbers of red blood cells 

What other tests might I have along with this test?

You may have a blood test that measures the red blood cells in your blood and the amount of oxygen carried by your red blood cells. These tests are called hemoglobin and hematocrit.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

The direct antiglobulin test tells your healthcare provider whether you or your child has antibodies to red blood cells. A negative result will find no antibodies to red blood cells. If there are any antibodies to red blood cells, the test is considered positive. The test results may range from 1+ (barely positive) to 4+ (very positive). A positive antiglobulin test may mean:

• Reaction to a blood transfusion

• Autoimmune hemolytic anemia

• Hemolytic disease of the newborn

• Hemolytic anemia caused by reactions to medicines

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

What might affect my test results?

Some medicines can interfere with this test. And some medicines can cause the test to come back positive even though you don't have hemolytic anemia. Medicines that may cause a positive test result include:

• Certain antibiotics, such as penicillin

• Anti-inflammatory medicines

• Antiplatelet medicines, such as clopidogrel

• Chemotherapy medicines

How do I get ready for this test?

You don't need to prepare for this test. Tell your healthcare provider about all medicines, herbs, or supplements you are taking. This includes medicines that don’t need a prescription and any illegal drugs you may use.