Coombs Test
Also written as DAT.
The direct antiglobulin (Coombs) test is positive at 4°C and negative at 37°C.
What our notes say
- The direct antiglobulin (Coombs) test is positive at 4°C and negative at 37°C. (hematopathology — Past Paper Questions & Answers)
- These tests, also known as Coombs tests, are critical for detecting antibodies involved in haemolytic conditions. (Blood Transfusion Medicine: An Exam-Focused Review)
- Maternal and baby blood groups (ABO and rhesus) and the direct Coombs test to look for immune haemolysis. (Paediatrics Year 4 MBChB end of semester CAT: triage, newborn care, growth and d)
- @ Direct-antiglobulin-(Coombs) test b a) Indirect antiglobulin test (HEMATOLOGY EOY 2025 — Past Paper Questions & Answers)
- He has a negative direct and indirect antiglobulin (Coombs) test. (hematopathology — Past Paper Questions & Answers)
- Direct Coombs test (DAT) — distinguishes immune (positive) from non-immune haemolysis (Hematopathology MCQs & Essays: MBChB Exam Revision Guide)
Study material on Coombs Test
Practice questions on Coombs Test
A 68-year-old man receives a blood transfusion. Within minutes he develops fever, rigors, back pain, hypotension, and hemoglobinuria. Direct Coombs test on post-transfusion sample is positive. Most likely type of transfusion reaction?
- Febrile non-hemolytic transfusion reaction
- Transfusion-related acute lung injury
- Acute hemolytic transfusion reaction
- Anaphylactic transfusion reaction
Answer: C. Immediate fever + back pain + hypotension + hemoglobinuria + positive Coombs = acute hemolytic transfusion reaction. Most often caused by ABO incompatibility from clerical error. Complement-mediated intravascular hemolysis is rapidly life-threatening. ---
A 45-year-old man receives a blood transfusion and develops a low-grade fever and mild chills during the infusion. No hemoglobinuria, no hypotension, no dyspnea. Direct Coombs test is negative. Most likely transfusion reaction?
- Acute hemolytic transfusion reaction
- Anaphylactic transfusion reaction
- Febrile non-hemolytic transfusion reaction
- Transfusion-associated circulatory overload
Answer: C. Mild fever and chills during transfusion + no hemolysis + negative Coombs = febrile non-hemolytic transfusion reaction. Caused by recipient antibodies against donor leukocyte antigens or cytokines in stored blood. The most common transfusion reaction. Managed by slowing or stopping transfusion and giving antipyretics. ---
A 25-year-old man receives a blood transfusion during surgery. Ten days later he develops jaundice, a falling hemoglobin, and a newly positive direct Coombs test. He had no immediate reaction during the transfusion. Most likely explanation?
- Febrile non-hemolytic transfusion reaction
- Transfusion-associated graft-versus-host disease
- Delayed hemolytic transfusion reaction
- Acute hemolytic transfusion reaction
Answer: C. Jaundice + falling hemoglobin + positive Coombs appearing 5–10 days after transfusion = delayed hemolytic transfusion reaction. Caused by an anamnestic antibody response to donor RBC antigens (commonly Kidd, Duffy, or Kell) from prior sensitization. ---
A 72-year-old man has increasing fatigue for a year. CBC: Hgb 9.1, MCV 96, WBC 3700, platelets 125,000. WBC differential shows 2 metamyelocytes, 1 myelocyte, and 5 nucleated RBCs/100 WBCs. Direct and indirect Coombs tests are negative. Most likely disease?
- Metastatic carcinoma
- Chronic alcoholism
- Malabsorption
- Systemic lupus erythematosus
Answer: A. Immature WBCs (metamyelocytes, myelocytes) + nucleated RBCs in peripheral blood = leukoerythroblastic picture from myelophthisic process. Metastatic carcinoma invading marrow displaces normal hematopoiesis, releasing immature cells into blood. ---
A 62-year-old man has 4 months of fatigue, abdominal discomfort, non-tender cervical lymphadenopathy, hepatomegaly, and splenomegaly. CBC: WBC 23,100 with 78% lymphs, Hgb 11.9, platelets 277,300. Direct Coombs test is positive. Most likely diagnosis?
- Leukemoid reaction
- Chronic myelogenous leukemia
- Acute myelogenous leukemia
- Chronic lymphocytic leukemia
Answer: D. Marked lymphocytosis (78%) + hepatosplenomegaly + lymphadenopathy + positive Coombs (autoimmune hemolysis) in an older adult = chronic lymphocytic leukemia (CLL). Most circulating cells are small mature lymphocytes. ---
A 73-year-old woman has 7 months of fatigue, 3 kg weight loss, and hands that turn purple and painful in the cold. Exam shows a palpable spleen tip. CBC: Hgb 10.5, MCV 99, platelets 193,600, WBC 5390. Direct Coombs test is positive at 4°C and negative at 37°C. Most likely underlying disease?
- Non-Hodgkin lymphoma
- Systemic lupus erythematosus
- Pernicious anemia
- Scleroderma
Answer: A. Cold-induced color change + positive Coombs at 4°C (cold agglutinins) + splenomegaly = cold autoimmune hemolytic anemia. In an elderly patient with weight loss, underlying non-Hodgkin lymphoma must be excluded as the driving cause. ---