Coombs Test (Antiglobulin Test)
Coombs Test (Antiglobulin Test)
The Coombs test is a crucial diagnostic tool in pediatric hematology used to detect antibodies against red blood cells (RBCs). It exists in two forms: direct and indirect antiglobulin tests.
Key Points
- Essential for diagnosing hemolytic disease of the newborn (HDN)
- Critical in evaluating autoimmune hemolytic anemia
- Used in blood compatibility testing
- Helps identify maternal antibodies in neonatal jaundice
Direct Coombs Test (DCT)
Principle
The direct Coombs test detects antibodies or complement proteins bound to RBC surface in vivo.
Indications
- Suspected autoimmune hemolytic anemia (AIHA)
- Hemolytic disease of the newborn
- Drug-induced hemolytic anemia
- Post-transfusion reactions
Procedure
- Patient's RBCs are washed to remove free proteins
- Anti-human globulin reagent is added
- Agglutination indicates positive result
Indirect Coombs Test (ICT)
Principle
The indirect Coombs test detects free antibodies in patient's serum capable of binding to RBCs.
Indications
- Prenatal screening
- Pre-transfusion testing
- Investigation of delayed hemolytic transfusion reactions
- Rh negative mothers during pregnancy
Procedure
- Patient's serum is incubated with known RBCs
- Cells are washed
- Anti-human globulin is added
- Agglutination indicates positive result
Clinical Applications
Neonatal Applications
- Screening for HDN
- Monitoring severity of hemolysis
- Guide exchange transfusion decisions
- Follow-up of affected infants
Pediatric Applications
- Diagnosis of AIHA
- Investigation of unexplained anemia
- Monitoring treatment response
- Evaluation of transfusion reactions
Result Interpretation
Direct Coombs Test Results
- Positive:
- Autoimmune hemolytic anemia
- ABO incompatibility
- Rh incompatibility
- Drug-induced hemolysis
- Negative:
- Normal finding
- Does not exclude mild hemolysis
- May be falsely negative in severe hemolysis
Indirect Coombs Test Results
- Positive:
- Presence of maternal antibodies
- Previous sensitization
- Recent transfusion reaction
- Negative:
- No circulating antibodies
- Compatible cross-match
