Which situation will cause a positive DAT Direct antiglobulin test in the newborn?
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Direct antiglobulin test; Indirect antiglobulin test; Anemia - hemolytic The Coombs test looks for antibodies that may stick to your red blood cells and cause red blood cells to die too early. A
blood sample is needed. No special preparation is necessary for this test. When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may
be some throbbing or slight bruising. This soon goes away. There are two types of the Coombs test: The direct Coombs test is used to detect antibodies that are stuck to the surface of red blood cells. Many diseases and drugs can cause this to happen. These antibodies sometimes destroy red blood cells and cause
anemia. Your health care provider may recommend this test if you have signs or symptoms of anemia or jaundice (yellowing of the skin or eyes). The indirect Coombs test looks for antibodies that are floating in the blood. These antibodies could act against certain red blood cells. This test is most often done to determine if you may have a reaction to a blood transfusion.
A normal result is called a negative result. It means there was no clumping of cells and you have no antibodies to red blood cells. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results. What Abnormal Results MeanAn abnormal (positive) direct Coombs test means you have antibodies that act against your red blood cells. This may be due to:
The test result may also be abnormal without any clear cause, especially among the older people. An abnormal (positive) indirect Coombs test means you have antibodies that will act against red blood cells that your body views as foreign. This may suggest:
RisksThere is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others. Other risks associated with having blood drawn are slight, but may include:
ReferencesElghetany MT, Banki K. Erythrocytic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 33. Michel M. Autoimmune and intravascular hemolytic anemias. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 151. Version InfoLast reviewed on: 1/25/2022 Reviewed by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.  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:
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:
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:
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. What causes a positive direct antiglobulin test?A positive direct antiglobulin test result may be the first indication of an immune response to a recent transfusion. The patient's developing antibodies will coat transfused RBCs bearing the corresponding antigen, resulting in a positive direct antiglobulin test result.
What causes a positive DAT test?Clinically significant in vivo causes of DAT positivity include AIHA, either due to warm or cold reactive antibodies, drug-induced positive DAT with or without hemolytic anemia, hemolytic transfusion reactions, hemolytic disease of fetus or newborn, and autoimmune disorders such as SLE and certain malignancies.
When is direct antiglobulin test positive?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.
What is are the clinical conditions that can result in a positive direct antiglobulin test?Clinical conditions that can result in positive DAT include AIHA, drug-induced hemolytic anemia, HDN, investigation of hemolytic transfusion reactions, and PLS. Positive DAT is the diagnostic hallmark of AIHA; however, it may be absent in some cases.
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