Coombs Test: What It Detects and When You Need It

What Is the Coombs Test?

The Coombs test, also known as the antiglobulin test, is a blood test used to detect antibodies that attack red blood cells (RBCs). These antibodies can lead to premature destruction of RBCs, a condition called haemolysis. The Coombs test helps diagnose autoimmune haemolytic anaemia, transfusion reactions, and haemolytic disease of the newborn.

Types of Coombs Test: Direct vs Indirect

The two types of Coombs tests are indirect and direct Coombs tests, and both serve different purposes:

• Direct Coombs Test (DCT): Also called the direct antiglobulin test (DAT), this test detects antibodies or complement proteins bound to the surface of RBCs. A positive DCT indicates autoimmune haemolytic anaemia or a transfusion reaction.
• Indirect Coombs Test (ICT): The ICT screens for free antibodies in the serum that could potentially attack RBCs. It is used to check for compatibility before blood transfusions and to screen pregnant women for antibodies that may cross the placenta and harm the foetus.

Why Is the Coombs Test Done?

The Coombs test's purpose is to diagnose conditions that cause premature destruction of red blood cells. Your doctor may order this test if you have symptoms of anaemia, such as fatigue, shortness of breath, or pale skin.

The Coombs test is also performed in the following situations:

• To investigate the cause of hemolytic anaemia
• Before blood transfusions to ensure compatibility
• To diagnose autoimmune disorders like lupus or rheumatoid arthritis
• To monitor pregnant women for antibodies that could harm the foetus
• To evaluate newborns for haemolytic disease of the newborn

How Is the Coombs Test Performed?

The Coombs test procedure involves drawing a sample of blood from a vein in your arm. For infants, a small amount of blood may be taken from the heel. The sample is sent to a lab where it is mixed with anti-human globulin (AHG) reagent. If antibodies are present, they will bind to the AHG and cause visible clumping of the RBCs.

No special preparation is needed for the Coombs test. You can eat and drink normally before the blood draw. The procedure is generally quick and carries minimal risks, such as slight pain or bruising at the injection site.

Interpreting Coombs Test Results

Interpretation of Coombs test results depends on the type of test performed:

• A positive direct Coombs test result means antibodies are attached to the surface of RBCs, indicating autoimmune haemolytic anaemia or a recent transfusion reaction.
• A positive indirect Coombs test result detects free antibodies in the serum that could attack transfused RBCs or cross the placenta and harm the foetus in pregnant women.
• A negative Coombs test result means no significant antibodies were found. However, a negative result does not always rule out an immune-mediated RBC disorder, as the test may not detect all types of antibodies.

Conditions Diagnosed Using the Coombs Test

The Coombs test purpose is to diagnose various disorders that involve destruction of red blood cells by antibodies:

• Autoimmune haemolytic anaemia (AIHA): The body produces antibodies that mistakenly attack its own RBCs.
• Drug-induced immune haemolytic anaemia: Certain medications trigger antibodies that target RBCs.
• Haemolytic transfusion reactions: Antibodies in the recipient's blood attack transfused RBCs.
• Haemolytic disease of the foetus and newborn (HDFN): Maternal antibodies cross the placenta and destroy foetal RBCs.

Coombs Test During Pregnancy

The indirect Coombs test is a routine prenatal screening test to detect maternal antibodies that could potentially harm the foetus. If the test is positive, it means the mother has been sensitised to foetal RBC antigens, usually due to a previous pregnancy or blood transfusion.

Sensitised mothers are monitored closely throughout pregnancy with repeated Coombs tests. If the foetus is found to be at risk for HDFN, early interventions such as intrauterine transfusions may be necessary to prevent severe anaemia and other complications.

Coombs Test for Newborn Babies

Newborns who develop jaundice or anaemia may undergo a direct Coombs test to check for antibodies attached to their RBCs. A positive DCT in a newborn indicates HDFN, which occurs when maternal antibodies cross the placenta and attack foetal red blood cells.

Prompt diagnosis with the Coombs test allows for timely treatment of HDFN, which may include phototherapy, intravenous immunoglobulin (IVIG), or exchange transfusions to manage severe anaemia and prevent kernicterus, a type of brain damage associated with high bilirubin levels.

Risks and Limitations of the Test

The Coombs test is a safe and low-risk procedure. As with any blood test, there is a slight chance of pain, bleeding, or infection at the injection site. Some people may feel dizzy or faint during the blood draw.

Certain factors may interfere with the Coombs test results, leading to false positives or negatives:

• Medications like penicillin, cephalosporins, and non-steroidal anti-inflammatory drugs (NSAIDs)
• Monoclonal antibodies used to treat cancer and autoimmune diseases
• Myeloma proteins in multiple myeloma patients

Conclusion: Importance of the Coombs Test in Modern Diagnostics

The Coombs test helps detect antibodies that destroy red blood cells, aiding diagnosis of autoimmune disorders, transfusion reactions, and Rh incompatibility in newborns. It is especially useful for pregnant women and those needing blood transfusions. Early detection helps prevent severe complications like haemolytic disease of the newborn.

At Metropolis Healthcare, we offer convenient at-home collection and fast, accurate results. The Coombs test price is affordable and ensures timely insights for effective treatment. Book your test today and take control of your health with trusted diagnostics from Metropolis.

FAQs

What is the difference between direct and indirect Coombs tests?

The direct Coombs test detects antibodies already attached to RBCs, while the indirect Coombs test identifies free antibodies in the serum that could potentially attack RBCs.

Is the Coombs test painful?

The Coombs test involves drawing blood from a vein, which may cause slight pain or discomfort. However, the procedure is generally quick and well-tolerated.

Do I need to fast before the Coombs test?

No, you do not need to fast or make any special preparations before the Coombs test.

Why is the Coombs test done in pregnancy?

The indirect Coombs test is performed during pregnancy to screen for maternal antibodies that could cross the placenta and attack foetal RBCs, causing haemolytic disease of the foetus and newborn.

Can medications affect the test results?

Yes, certain medications like antibiotics, NSAIDs, and monoclonal antibodies can interfere with Coombs test results, causing false positives or negatives.