Tareq Abadl: Coombs Test Explained in a Simple and Clear Way
Tareq Abadl, Medical Laboratory Specialist and Director of the Blood Bank at Dr. Abdelkader Al-Mutawakkil Hospital, shared a post on LinkedIn:
”Coombs Test
…the blood cell detective!
In our lab, we have a famous detective called the Coombs Test. His main job is to uncover the presence of antibodies attacking red blood cells.
It’s not a simple case, because he has two investigation methods:
Direct Coombs Test
(the detective at the crime scene):
Steps:
- Take a blood sample from the patient.
- Wash the red blood cells to remove plasma or free antibodies.
- Add a reagent called Anti-human globulin.
- If antibodies or complement are stuck on the surface of red blood cells then Agglutination occurs (clumping of RBCs).
Used in cases like:
- Autoimmune hemolytic anemia.
- Transfusion reactions.
- Hemolytic disease of the newborn.
A positive result means: ‘the crime has already happened’, meaning antibodies are bound to RBCs and destroying them.
Indirect Coombs Test
(the detective among the suspects):
Steps:
- Take the patient’s serum (plasma).
- Add reagent red blood cells with known composition.
- If antibodies are present in the serum, they bind to the added RBCs.
- Add Anti-human globulin reagent.
- If agglutination occurs, it means free antibodies are present in the serum.
Commonly used in:
- Cross-matching before blood transfusion to ensure compatibility.
- Antenatal screening for mothers to detect antibodies that may affect the fetus.
A positive result means: ‘there are hidden criminal intentions’ meaning antibodies in the serum that could cause future problems.
Key difference:
- Direct test focuses on crimes that already happened.
- Indirect test focuses on potential crimes in the future.
Both rely on the same principle:
Using Anti-human globulin reagent to detect antibodies, with results shown as agglutination.”
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