Direct Coombs Test
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Was ist Direct Coombs Test?
The direct Coombs test, also known as the direct antiglobulin test (DAT), detects antibodies or complement proteins that are bound directly to the surface of red blood cells (RBCs) in vivo. The test is performed by washing the patient's red blood cells to remove unbound proteins, then adding anti-human globulin (AHG, also called Coombs reagent). If IgG antibodies or complement component C3d are attached to the RBC surface, the AHG will cross-link them, causing visible agglutination.
The DAT is a cornerstone of transfusion medicine and hematology. It is the primary test for diagnosing autoimmune hemolytic anemia (AIHA), evaluating transfusion reactions, investigating hemolytic disease of the fetus and newborn (HDFN), and detecting drug-induced immune hemolysis. The strength of the agglutination reaction is graded from 1+ to 4+, with stronger reactions generally correlating with more significant antibody coating, though clinical severity does not always parallel DAT strength.
Warum der Wert wichtig ist
The direct Coombs test is essential for determining whether hemolysis (red blood cell destruction) is immune-mediated. A positive DAT in the setting of anemia and evidence of hemolysis (elevated LDH, low haptoglobin, elevated indirect bilirubin, reticulocytosis) confirms autoimmune hemolytic anemia and guides treatment. It is also critical in evaluating transfusion reactions—a newly positive DAT after transfusion suggests an acute or delayed hemolytic transfusion reaction. In newborns with jaundice, a positive DAT helps confirm hemolytic disease of the newborn.
Normale Referenzbereiche
| Gruppe | Bereich | Einheit |
|---|---|---|
| Adults and children | Negative | (no agglutination) |
Referenzbereiche können je nach Labor variieren. Vergleichen Sie Ihre Ergebnisse immer mit den Bereichen Ihres Testlabors.
Was hohe DAT-Werte bedeuten
Häufige Ursachen
- Warm autoimmune hemolytic anemia (IgG-mediated)
- Cold agglutinin disease (complement-mediated)
- Drug-induced immune hemolytic anemia (penicillin, cephalosporins, methyldopa)
- Hemolytic transfusion reactions
- Hemolytic disease of the fetus and newborn (Rh or ABO incompatibility)
- Systemic lupus erythematosus
- Chronic lymphocytic leukemia
- Evans syndrome (AIHA + immune thrombocytopenia)
Mögliche Symptome
- Fatigue and weakness
- Jaundice (yellowing of skin and eyes)
- Dark urine (hemoglobinuria)
- Pallor
- Rapid heart rate
- Shortness of breath
- Splenomegaly (enlarged spleen)
Was zu tun ist: A positive DAT should be interpreted alongside clinical findings: complete blood count, reticulocyte count, haptoglobin, LDH, and indirect bilirubin. Monospecific DAT (testing separately for IgG and C3d) helps classify the type of immune hemolysis and guide therapy. Warm AIHA (IgG-positive) is typically treated with corticosteroids, while cold agglutinin disease (C3d-positive) responds poorly to steroids and may require rituximab. Drug causes should be investigated and the offending agent discontinued.
Was niedrige DAT-Werte bedeuten
Häufige Ursachen
- Normal result—no antibodies or complement bound to RBCs
- DAT-negative autoimmune hemolytic anemia (rare, ~5% of AIHA cases)
Mögliche Symptome
- No symptoms associated with a negative DAT
Was zu tun ist: A negative DAT is the expected normal result. If clinical suspicion for immune hemolysis is high despite a negative DAT, more sensitive techniques such as flow cytometry, gel-based DAT, or eluate studies may detect low-level antibody coating not detected by standard tube methods.
Wann wird ein DAT-Test empfohlen?
- Evaluating unexplained hemolytic anemia
- Investigating a suspected transfusion reaction
- Workup of neonatal jaundice or hemolytic disease of the newborn
- Suspected drug-induced hemolysis
- Autoimmune disease workup with cytopenias
Häufig gestellte Fragen
Verwandte Biomarker
Weiterführende Inhalte
Erkrankungen
Quellen- und Prüfungsansatz
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