Overview
Autoimmune Hemolytic Anemia (AHA) is a group of anemias caused by increased hemolysis due to antibodies directed against the patient's own red blood cells. These autoantibodies are usually immunoglobulins (Ig type).
AHA is classified both etiologically (idiopathic vs secondary to drugs or disease) and by the temperature at which the antibody reacts with red cells (warm vs cold), each with distinct clinical behavior and mechanisms of hemolysis.
Learning Objectives
After this lesson you will be able to…- Define autoimmune hemolytic anemia.
- Classify autoimmune hemolytic anemia by etiology and antibody temperature.
- Explain the diagnostic approach to autoimmune hemolytic anemia.
- List common drug and disease causes of secondary AHA.
- Differentiate warm and cold antibody-mediated hemolysis.
Clinical Story
Why This MattersAn elderly woman with known systemic lupus erythematosus develops sudden fatigue and jaundice. Her hemoglobin has dropped from 12 to 7 g/dL in two weeks. The lab technologist runs a Direct Coomb's test which turns strongly positive, and the reticulocyte count is elevated — confirming secondary autoimmune hemolytic anemia related to her underlying lupus, guiding the rheumatologist toward immunosuppressive therapy.
Core Concepts
AHA is idiopathic in about 50% of cases. Secondary causes include drugs (methyl dopa, mefenamic acid, L-dopa, procainamide) and diseases such as malignancy of the lymphoreticular system, SLE, rheumatoid arthritis, ulcerative colitis, paroxysmal cold hemoglobinuria (PCH), and infections like Mycoplasma pneumonia and CMV.
Warm antibodies combine with red cells at 37°C, are typically IgG, may or may not fix complement, and cause extravascular hemolysis in the spleen. Secondary causes include lymphomas, SLE, infections and drugs like methyldopa. Cold antibodies have little activity at 37°C but increase in affinity as temperature falls to 30–32°C down to 24°C; they are usually IgM, fix complement, and cause intravascular hemolysis. Cold agglutinin disease may be idiopathic or secondary to Mycoplasma pneumonia, infectious mononucleosis, lymphomas or PCH.
Tests for hemolysis: complete blood count with peripheral smear, serum bilirubin, LDH, serum haptoglobin, and urine hemoglobin. Serological test: the diagnosis of AHA depends on demonstrating autoantibodies on the surface of red cells using the antiglobulin test — adding AHG serum causes affected red cells to agglutinate.
Laboratory Principle
Autoantibodies bind red cell surface antigens, marking these cells for premature removal. Warm IgG antibodies typically opsonize red cells for extravascular destruction by splenic macrophages, while cold IgM antibodies fix complement efficiently, causing intravascular lysis. The Direct Antiglobulin Test detects these bound autoantibodies or complement fragments using AHG reagent, which bridges sensitized cells to produce visible agglutination.
Equipment Required
Reagents & Materials
| Reagent / Material | Concentration / Grade | Purpose | Storage |
|---|---|---|---|
| Antihuman globulin (AHG) serum | Polyspecific/monospecific | Detects autoantibodies/complement on RBC surface | 2–8°C |
| Normal saline | 0.9% | Washing red cells before AHG addition | Room temperature |
| EDTA anticoagulated blood | Whole blood sample | Specimen for CBC, smear and DAT | 2–8°C |
Step-by-Step Procedure
Perform complete blood count with peripheral blood smear examination for spherocytes, agglutination or polychromasia.
Measure serum bilirubin (indirect), LDH, serum haptoglobin and urine hemoglobin.
Wash patient red cells, add AHG serum, centrifuge and examine for agglutination to confirm autoantibody/complement on cell surface.
Assess reactivity at 37°C vs 4°C to classify warm vs cold antibody-mediated AHA.
Screen for secondary causes — drug history, autoimmune disease markers (ANA), lymphoproliferative work-up, or recent infection.
Flow Diagram
Quality Control
Always confirm negative DAT results with a positive control (IgG-coated cells) before finalizing the report, as with all Coomb's-based testing.
Participate in immunohematology EQAS to validate consistent DAT grading and warm/cold antibody differentiation across shifts and technologists.
Reference Values
Normal Ranges⚠️ Reference ranges may vary between laboratories. Always apply your laboratory's established reference intervals.
Clinical Interpretation
| Finding | Possible Significance | Action / Follow-up |
|---|---|---|
| Positive DAT reacting at 37°C, spherocytes on smear | Warm AIHA | Screen for lymphoma, SLE, drug cause; start steroids if idiopathic |
| Positive DAT reacting at cold temperatures, agglutination on smear | Cold agglutinin disease | Screen for Mycoplasma, lymphoma; keep patient warm |
| Negative DAT despite clinical hemolysis | Non-immune hemolytic anemia | Investigate for enzyme defects, membrane defects, or mechanical fragmentation |
Common Errors & How to Avoid Them
Cause: Testing only at 37°C misses cold-reactive antibodies that peak at 4°C.
Prevention: If cold AIHA is suspected, test at multiple temperatures and keep sample/reagents warm during collection and processing to avoid loss of cold antibody reactivity.
Cause: Red cell clumping from cold agglutinins falsely elevates MCV and MCHC on automated analyzers.
Prevention: Warm the sample to 37°C before running it through the automated counter.
Cause: Secondary causes (lymphoma, SLE, drugs) are common and easily missed without a thorough history and screening.
Prevention: Always screen for secondary causes before labeling AHA as idiopathic.
Laboratory Tips from the Bench
Spherocytes on smear strongly suggest warm AIHA, while red cell agglutination/clumping suggests cold agglutinin disease.
Always take a careful drug history — methyldopa, mefenamic acid, L-dopa and procainamide are classic drug triggers for secondary AHA.
"Warm hugs at body temperature, Cold snaps in the cold" — warm antibodies react at 37°C (extravascular); cold antibodies react below body temperature (intravascular).
Important Notes
About 50% of AHA cases are idiopathic and 50% are secondary to drugs or disease — a thorough clinical work-up is essential in every case.
Warm antibodies are typically IgG and may or may not fix complement; cold antibodies are typically IgM and efficiently fix complement, causing intravascular hemolysis.
Interactive Quiz
Test Your KnowledgeFlashcards
Tap to flipClick or tap any card to reveal the answer.
Clinical Case Study
Apply Your KnowledgePresents with progressive fatigue, jaundice and dark urine over two weeks. Known history of systemic lupus erythematosus on low-dose steroids.
A positive IgG-type Direct Coomb's test with spherocytes and reticulocytosis in a patient with known SLE indicates secondary warm autoimmune hemolytic anemia.
- →SLE is a well-recognized secondary cause of warm AIHA.
- →Spherocytes on smear point toward warm-antibody mediated hemolysis.
- →Treatment targets the underlying autoimmune disease alongside hemolysis management.
Frequently Asked Questions
Yes — this is called mixed-type AIHA, where both warm IgG and cold IgM antibodies are present, often producing a more severe or complex clinical picture.
Drug-induced immune hemolytic anemia typically resolves once the offending drug is withdrawn, as the antibody production is directly triggered by the drug.
Since cold antibodies have increasing affinity for red cells as temperature drops, keeping the patient warm reduces antibody binding and complement fixation, minimizing hemolysis.
Quick Revision
10-Minute ReviewKey Takeaways
- AHA is defined by antibody-mediated destruction of the patient's own red cells.
- Classification is based on etiology (idiopathic/secondary) and antibody temperature (warm/cold).
- Warm AIHA is IgG-mediated, extravascular; cold agglutinin disease is IgM-mediated, intravascular.
- Diagnosis requires both hemolysis markers and a positive antiglobulin test.
- Secondary causes span drugs, autoimmune diseases, malignancies and infections.
- Treatment targets both hemolysis and any identified underlying cause.
Competency Checklist
Track Your MasteryReferences
- NIOS Hematology and Blood Bank Technique — Lesson 25: Autoimmune Hemolytic Anemia (AHA).
- Dacie JV, Lewis SM. Practical Haematology. 11th ed.