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Coombs Test

The Coombs Test is a serological test used to detect antibodies against red blood cells, which can lead to hemolysis. There are two types: the Direct Coombs Test (DCT) detects antibodies bound to RBCs in the body, while the Indirect Coombs Test (ICT) detects free antibodies in serum. The test is crucial for diagnosing conditions like autoimmune hemolytic anemia and for cross-matching blood transfusions.

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12 views2 pages

Coombs Test

The Coombs Test is a serological test used to detect antibodies against red blood cells, which can lead to hemolysis. There are two types: the Direct Coombs Test (DCT) detects antibodies bound to RBCs in the body, while the Indirect Coombs Test (ICT) detects free antibodies in serum. The test is crucial for diagnosing conditions like autoimmune hemolytic anemia and for cross-matching blood transfusions.

Uploaded by

samarth.srivastava2014
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We take content rights seriously. If you suspect this is your content, claim it here.
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🔹 What is the Coombs Test?

It’s a serological test used to detect antibodies that act against the surface of red blood cells
(RBCs). These antibodies can cause hemolysis.

Developed by Robin Coombs, hence the name.

🔹 Types of Coombs Test


1. Direct Coombs Test (DCT / DAT)

●​ Principle: Detects antibodies or complement proteins already bound to RBCs


inside the patient’s body.
●​ Procedure:
○​ Patient’s RBCs are washed → incubated with Coombs reagent (anti-human
globulin) → if antibodies/complement are present → RBCs agglutinate (positive
test).
●​ Clinical Uses:
○​ Autoimmune hemolytic anemia (AIHA)
○​ Hemolytic disease of the newborn (HDN)
○​ Hemolysis after blood transfusion reaction
○​ Drug-induced immune hemolysis

2. Indirect Coombs Test (ICT / IAT)

●​ Principle: Detects free (unbound) antibodies against RBCs present in the patient’s
serum.
●​ Procedure:
○​ Patient’s serum is mixed with test RBCs → then Coombs reagent added →
agglutination occurs if antibodies were present in serum.
●​ Clinical Uses:
○​ Cross-matching before blood transfusion
○​ Antibody screening in pregnant women (Rh incompatibility)
○​ Detection of alloantibodies in transfusion medicine
🔹 Coombs Reagent
●​ Anti-human globulin (AHG) = antibodies against human IgG and complement (C3d).
●​ Can be polyspecific (IgG + C3d) or monospecific (IgG only).

🔹 Interpretation
●​ Positive Coombs test → immune-mediated hemolysis or presence of RBC antibodies.
●​ Negative → no antibody-mediated reaction on RBCs.

✅ Quick memory trick:


●​ Direct = Detects antibodies Directly on RBCs (in vivo).
●​ Indirect = Detects antibodies Indirectly in serum (in vitro).

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