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Coombs Direct

Also known as

DAT, Direct Coombs Test, Direct Anti-human Globulin Test

This test helps diagnose why red blood cells are being destroyed – also known as hemolytic anemia. It also diagnoses hemolytic disease in a newborn. It also investigates reactions to blood transfusions.
You need to get tested if you have had a blood transfusion reaction and are exhibiting signs of an adverse transfusion reaction like back pain, shortness of breath, and dizziness. It is ordered for newborns when they show symptoms of hemolytic disease. It is also ordered when patients indicate signs of the destruction of red blood cells, such as feeling tired constantly, headaches, paleness, shortness of breath.
This is a blood test. A sample of blood is drawn from a vein in your arm via a syringe.
There is no special preparation needed for the test.
This test identifies whether the red blood cell in your body are in circulation in the bloodstream covered with antibodies. These antibodies cling to the surface of your red blood cells, eventually causing their destruction. There are four main triggers for the attack by antibodies:
  1. After a blood transfusion: when someone receives blood that does not match their type, the body's immune response is to identify the blood as foreign and launch an attack against the red blood cells and destroy them. People that have had multiple blood transfusions make more red blood cells because of their exposure to foreign red blood cells. If someone shows symptoms of a reaction to a blood transfusion, the test helps determine if there are antibodies attached to the surface of the red blood cells.
  2. Mother’s or baby’s blood types are incompatible: the baby might have a blood type different from that of the mother if he or she inherits it from the father. Sometimes in labor, a mother may get exposed to a baby's red blood cells, which may be recognized by the immune system as a foreign, and immune response may be triggered. In other cases, a baby's red blood cells can be covered with antibodies that cross into the placenta from the mother's blood into his/her blood circulation. This leads to the antibodies attacking the baby's red blood cells, causing hemolytic disease of the newborn. The test helps determine if there are antibodies from the mother attached to the baby's red blood cells.
  3. Autoimmune disease and other conditions: in some cases, people may make antibodies that attack their red blood cells. The production of these antibodies occurs because the immune system mistakenly identifies the body's own red blood cells as foreign invaders. This occurs in various conditions like autoimmune disorders such as lupus Anticoagulant , malignant disease like lymphoma and chronic lymphocytic leukemia, and infections like mononucleosis.
  4. Drug-induced anemia: in some cases, drugs can cause the production of antibodies against red blood cells leading to their destruction. This occurs with antibiotics like penicillin, piperacillin, and cephalosporins. Therefore, it is important to notify your doctor about any drugs you have been on.
The test is used by the doctor to determine the root cause of hemolytic anemia, hemolytic disease of the newborn, and a suspected reaction to blood transfusions.
This test can be ordered in various situations. It is ordered by your doctor when you have hemolytic anemia, and he or she wants to figure out the root cause of the disease. It is also ordered by the doctor when a baby is born to someone who is at-risk or has shown symptoms of hemolytic disease of the newborn. If there is no definite cause, there are some symptoms that may help in the diagnosis, such as
  1. Pale appearance
  2. Jaundice, including elevated bilirubin
  3. Enlarged liver or spleen
  4. Swelling of the entire body
  5. Difficulty breathing
Lastly, Coombs Direct is ordered when a patient has had a blood transfusion and has been showing symptoms of a blood transfusion reaction like
  1. Fever, chills
  2. Back pain
  3. Bloody urine
A positive test result indicates that antibodies are attached to red blood cells. The stronger the reaction/positive the test, the greater number of antibodies are attached to the red blood cell. However, this is not linked to the severity of symptoms. The test is useful in identifying the presence of antibodies, but it does not indicate the cause or type of antibody. This is only determinable in conjunction with a medical history and clinical examination. Conditions that can lead to a strong DAT are:
  1. Transfusion reaction
  2. An autoimmune disorder, such as lupus
  3. Lymphoma or another malignant disease
  4. Infection, such as mycoplasma pneumonia and mononucleosis
  5. Medication, such as penicillin
  6. Baby-mother blood group incompatibility
People rarely test DAT positive and turn out not to have hemolytic anemia. A negative test result rules out the possibility of antibodies being attached to your red blood cells, but symptoms must be further investigated to find out what is causing them.