The Coombs test is a blood test that is designed to look for antibodies that could attack and destroy red blood cells. There are two types of Coombs tests, the direct Coombs test and indirect Coombs test. Also known as direct antiglobulin test (DAT), the direct Coombs test checks for antibodies that are attached to red blood cells at the surface. The indirect Coombs test procedure checks for unattached antibodies floating around in the bloodstream. This test is also carried out to find out if a blood transfusion has had a negative reaction to the body.
If the doctor feels that a patient is affected by hemolytic anaemia, he may suggest that the direct Coombs blood test be carried out. During hemolytic anaemia, there is a drastic reduction in the number of red blood cells in the body. The test provides insights to help the doctor understand if the body’s immune system itself is causing the drop in red blood cells.
The indirect Coombs test is used as a pointer by doctors to confirm if blood received during transfusion is compatible and will not cause any negative reaction in the body. It is also carried out during pregnancy to check if the antibodies present in the mother’s blood can cause any harm to the baby.
Our red blood cells are covered with proteins called antigens which act as signals that identify a foreign body. The body’s immune system acts on the antigens that are externally transmitted, through organ transplant, blood transfusion or pollen. In this manner, our body prevents us from being affected by illness by recognizing viruses and bacteria and destroying them. Our blood is classified by the various antigens that are present on the surface of the red blood cells. During blood transfusion or organ transplant, if the patient receives incompatible blood, the body’s immune system will destroy the new blood cells it sees as foreign bodies. This can cause serious illnesses or death if corrective measures are not taken quickly. For patients who develop severe, life-threatening anaemia, blood transfusion is often a part of coombs treatment even if the blood is incompatible.
A tiny sample of the patient’s blood is needed to carry out the Coombs test, in case of indirect or direct Coombs test procedure. This blood sample is then tested after it is combined with compounds that react with the antibodies in the bloodstream. A needle is inserted into a vein in the arm, and a small quantity of blood is drawn and stored in a test tube. When this test is carried out on infants if the mother has a different blood type, blood is drawn from the heel of the foot. The skin on the heel is pricked with a sharp needle called the lancet, and the blood is collected on a test slide. This ensures the least pain and discomfort to the baby.
Through the above discussions, most of us would have understood what is coombs and its applications. If the test results do not show any clusters of red blood cells, the test result can be said to be normal. However, clustering of red blood cells during the direct Coombs test procedure indicates the presence of antibodies on red blood cells and the patient may suffer from a condition called hemolysis.
‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’
The Coombs test remains a definitive guide for doctors to present a conclusive diagnosis for those affected by hemolytic anemia. If carried out at the right time, it can prove to be life-saving in many critical situations.
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