Coomb's test (Direct)

Antibodies are an essential component of our immune system. They help protect our bodies from infections, but sometimes they may attack the healthy cells of the body. Since all the red blood cells in the body are not alike, our immune system may produce antibodies against the ones that do not match the others. However, if the immune system cannot detect the infection correctly and starts producing antibodies against one's cells, it can cause several health problems.

The Coombs test detects the presence of antibodies that may attack the red blood cells. The Coombs test may help the doctor determine if the antibodies produced by the immune system are responsible for attacking and destroying one's RBCs. This kind of autoimmune destruction of the red blood cells is referred to as hemolytic anaemia.

Of the two Coombs tests, the Direct Coombs Test helps detect antibodies that are attached to the red blood cells. Otherwise known as the Direct Agglutination Test, the Direct Coombs Test is done more frequently. This is because the reagent used in the Coombs test causes the red blood cells with the attached antibodies to stick to each other.

A Direct Coombs Test can also be done to diagnose transfusion reaction and fatal conditions like erythroblastosis fetalis.

1. Usually, a blood sample is required to carry out a Direct Coombs test.
2. The blood is generally obtained from a vein through venipuncture.
3. This test can also be conducted on infants. To perform this test, the skin is pricked with a needle, usually on the foot's heel. The blood is usually collected in a small glass tube, slide or test strip.

Hemolytic anaemia, Erythroblastosis fetalis, Transfusion-related hemolysis, Autoimmune diseases, Adverse reactions to some medicines

The Direct Coombs test helps to diagnose hemolytic conditions.

A Direct Coombs test is done to detect:

Autoimmune diseases

Hemolysis can take place in autoimmune conditions. A positive Direct Coombs test can be expected in:

• Autoimmune hemolytic anaemia: A condition in which the immune system attacks its own red blood cells in the body.
• Malignancies like leukaemia.
• Autoimmune diseases like systemic lupus erythematosus and antiphospholipid syndrome.

Transfusion reaction

Immediately after transfusion, the immune system may attack the donated blood cells. This usually occurs when the blood donor type is not an appropriate match. This can show up as early as two days after the transfusion. The recipient may experience symptoms like dizziness, back pain, dark urine and shortness of breath.

Erythroblastosis fetalis

Erythroblastosis fetalis is a fatal condition in which the fetus and the parents have different blood types. The difference may be in the Rh factor or ABO blood type. As a result, the immune system of the mother may attack the red blood cells of the infant, which can result in their death. In addition, infants with erythroblastosis fetalis may develop jaundice due to their high bilirubin levels.

Infection

Certain infections like syphilis, mononucleosis, malaria and AIDS can cause hemolysis. This can be detected through the Direct Coombs test.

Adverse reactions to some medicines

Certain medicines like cephalosporins (antibiotics), dapsone (antibacterial) and painkillers like ibuprofen can cause the destruction of red blood cells.

The Direct Coombs test is not done frequently. It is usually ordered immediately when a newborn exhibits signs of hemolysis like pale appearance, jaundice, enlarged liver, difficulty in breathing and swelling of the entire body.

It is also advised when a person develops the signs of hemolysis immediately after blood transfusion.

It is also done when a doctor suspects the presence of hemolytic disease in the patient.

What to Expect During the Test

Before the Test

Usually, there's no need to make any special preparations for the direct coombs test. However, if your doctor has recommended this test along with another one that requires fasting, they might advise you to avoid certain foods. Talk to your doctor before any test for the best outcomes.

During the Test

A vein in your arm will be pricked to collect a blood sample. Here's what you can anticipate during the procedure:

• The site where the needle is inserted will be cleaned with an antiseptic solution.
• A tourniquet will be applied to your arm to make finding the veins easier.
• A needle will be inserted into the vein to draw blood. You might experience a quick pinch for a few seconds.
• The blood will be collected in a vial/tube, which will be labelled with your details.

After the Test

After the blood has been drawn:

• A bandage will be applied to the area where the needle was inserted to prevent any bleeding.
• It's normal to have some bruising. Some people might feel dizzy and should rest for a few minutes.
• In case of bleeding, pain, or rashes at the site of the puncture, it's important to reach out to your healthcare provider.

• IgM antibodies against RBC membrane
• IgG antibodies against the RBC membrane

The Direct Coombs test is used to detect the coating of red blood cells with IgG antibodies and complements like C3d.

Normal findings: Negative, no agglutination.

The normal values and reference ranges of the test may vary from lab to lab. Please refer to the ranges mentioned in the report and consult a doctor to understand the interpretation of lab reports.

The Coombs test detects the agglutination or formation of clumps of red blood cells.

The test is said to be negative when no clump is formed. A negative test usually indicates that antibodies are not attached to the red blood cells. This also signifies that the symptoms you are experiencing are probably due to another cause.

A positive Direct Coombs test result means that agglutination occurs and antibodies are attached to the red blood cells. Thus, the immune system plays a significant role in destroying red blood cells.

However, a positive Direct Coombs test does not always mean that hemolysis occurs. If hemolysis is suspected, a Direct Coombs test can be done to confirm the provisional diagnosis.

A Coomb test can have varying costs depending on the city and the laboratory. Typically, the price for a Coomb test falls between INR 259 and INR 769. Here's a breakdown of the average charges for a Coomb test in select major cities in India: