Direct Antiglobulin Test
Also written as DAT.
A blood sample sent to the hospital blood bank for crossmatching is found to have a positive direct antiglobulin test (DAT).
What our notes say
- A blood sample sent to the hospital blood bank for crossmatching is found to have a positive direct antiglobulin test (DAT). (Haematology paper 1 Past Papers — Past Paper Questions & Answers)
- Autoimmune haemolytic anaemia — IgG warm antibodies detected by direct antiglobulin test (Haematopathology MCQs: Blood Disorders & Anemia Explained)
- Immediate management: Stop further transfusion of incompatible units, send samples for direct antiglobulin test/antibody identification, and provide antigen-negative (extended phenotype-matched) blood for any further transfusion (Master Blood Transfusion: A Medical Quiz on Reactions & Tests)
- Investigations: ABO and Rh(D) grouping; Direct antiglobulin test (DAT) (Master Blood Transfusion: A Medical Quiz on Reactions & Tests)
- | Direct Antiglobulin Test (DAT) | Antibodies already bound to the patient's own RBCs in vivo | Haemolytic transfusion reactions; autoimmune haemolytic anaemia; HDN | (Blood Transfusion: ABO, Rh Blood Groups, Compatibility & HDN)
Study material on Direct Antiglobulin Test
- Master Blood Transfusion: A Medical Quiz on Reactions & Tests
- Blood Transfusion Medicine: An Exam-Focused Review
- Blood Transfusion: ABO, Rh Blood Groups, Compatibility & HDN
- Haematopathology MCQs: Blood Disorders & Anemia Explained
- Haematology paper 1 Past Papers
- Transfusion: Governance, Donor Selection & Blood Groups
- Dr. Orata Haematology MCQs: Past Paper Questions & Answers
- Master Blood Transfusion MCQs: Coagulation & Hematology
- MCQ: High-Yield MCQs — Haematology (All Topics)
- MCQ: Pathology
Practice questions on Direct Antiglobulin Test
Positive direct antiglobulin test (DAT) indicates?
- Antibodies in patient's serum
- Antibodies bound to patient's RBCs
- ABO incompatibility
- Hemolytic transfusion reaction
Answer: B. DAT detects IgG or complement already coating the patient's own RBCs in vivo. ---
The direct antiglobulin test (DAT/Coombs) detects
- Free antibodies in serum
- Antibodies or complement on the RBC surface
- ABO incompatibility only
- Cold agglutinins in plasma
Answer: B. DAT detects IgG or complement (C3d) already bound to red cells, confirming immune-mediated haemolysis. ---
A patient experiences an unexpected drop in haemoglobin and mild jaundice approximately 7 days after receiving a blood transfusion. A direct antiglobulin test (DAT) is positive. Which blood group system is most notoriously associated with this type of reaction?
- The ABO blood group system due to common pre-formed IgM antibodies.
- The Rh blood group system, often involving anti-D following Rh-positive exposure.
- The Duffy blood group system, known for its association with malaria resistance.
- The Kidd blood group system, notorious for causing anamnestic antibody responses.
Answer: D. The timing (3-10 days post-transfusion), fall in Hb, mild jaundice, and positive DAT are consistent with a delayed haemolytic transfusion reaction (DHTR). DHTRs occur when low-level alloantibodies, often not detected on initial antibody screens, are boosted by the transfused RBCs, leading to an anamnestic immune response. The Kidd blood group system is particularly notorious for causing these types of reactions, as K
A positive direct antiglobulin test (DAT) indicates ---
- Antibodies in patient's serum
- Antibodies bound to patient's RBCs DAT (direct Coombs) detects antibody/complement already coating the patient's own RBCs.
- ABO incompatibility
- Rh incompatibility
- Hemolytic transfusion reaction Answer:
Answer: A.