IgG-mediated extravascular hemolysis with positive direct Coombs (DAT) — first-line treatment is steroids.
Also known as: wAIHA, warm AIHA, autoimmune hemolytic anemia, warm-antibody hemolysis
Overview
Autoimmune hemolytic anemia caused by IgG autoantibodies that bind erythrocytes at body temperature (37°C). Antibody-coated cells are removed by splenic macrophages (extravascular hemolysis). May be primary (idiopathic, ~50%) or secondary to autoimmune disease, lymphoproliferative disorder, drug, or infection.
Epidemiology
Most common form of autoimmune hemolytic anemia (~75% of AIHA). Annual incidence ~1-3 per 100,000. Bimodal age distribution; can occur at any age but more common in adults. Slight female predominance.
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Question 1HematologyMedium
A 32-year-old female has fatigue and jaundice. Labs: hemoglobin 8.2 g/dL, MCV 88 fL, reticulocyte count 12%, elevated LDH, elevated indirect bilirubin, low haptoglobin, and a positive direct Coombs test. Which of the following is the most likely diagnosis?
AAutoimmune hemolytic anemia
BMicroangiopathic hemolytic anemia
CHereditary spherocytosis
DPyruvate kinase deficiency
Reveal answer & full explanation
Correct answer: A — Autoimmune hemolytic anemia
AAutoimmune hemolytic anemia✓
BMicroangiopathic hemolytic anemia
CHereditary spherocytosis
DPyruvate kinase deficiency
Why Autoimmune hemolytic anemia is correct
Hemolysis labs are present: elevated reticulocytes, elevated indirect bilirubin, elevated LDH, and low haptoglobin.
A positive direct Coombs test (direct antiglobulin test, DAT) confirms antibody-mediated RBC destruction, establishing the diagnosis.
The MCV is normocytic (88 fL), consistent with brisk hemolysis and a reticulocytosis rather than a nutritional or thalassemic cause.
Jaundice reflects unconjugated hyperbilirubinemia from RBC breakdown, and the low haptoglobin indicates intravascular consumption of free hemoglobin.
Why the others are wrong
Microangiopathic hemolytic anemia — mechanical RBC shearing (TTP, HUS, DIC, malignant hypertension) produces schistocytes with a negative direct Coombs test; the positive DAT here indicates antibody-mediated rather than shear-mediated destruction.
Hereditary spherocytosis — an inherited membrane-protein defect causing Coombs-negative hemolysis with spherocytes, splenomegaly, a family history, and a positive osmotic fragility or EMA-binding test; spherocytes with a positive DAT point to warm AIHA instead.
Pyruvate kinase deficiency — an autosomal recessive RBC enzymopathy causing chronic Coombs-negative hemolysis usually recognized in childhood; a positive DAT excludes an intrinsic enzyme defect as the cause.
Additional high-yield points
Warm AIHA (IgG): most common type; triggers include lymphoma, chronic lymphocytic leukemia (CLL), lupus, and drugs (alpha-methyldopa, penicillin); treat with corticosteroids, then rituximab or splenectomy.
Cold AIHA (IgM): triggered by Mycoplasma, mononucleosis, and Waldenström macroglobulinemia; treat by avoiding cold and treating the underlying cause; rituximab if needed.
Question 2HematologyMedium
A 44-year-old woman presents with two weeks of progressive fatigue, exertional dyspnea, and scleral icterus. She takes no medications and has no family history of anemia. Vitals show heart rate 104/min and a soft flow murmur; the spleen tip is palpable. Labs: hemoglobin 7.2 g/dL, MCV 104 fL, reticulocytes 9%, LDH elevated, indirect bilirubin elevated, and haptoglobin undetectable. The peripheral smear shows spherocytes and polychromasia, and the direct antiglobulin test (Coombs) is positive for IgG. Which of the following is the most appropriate initial management?
APrednisolone
BRituximab IV
CSplenectomy
DIVIG therapy
Reveal answer & full explanation
Correct answer: A — Prednisolone
APrednisolone✓
BRituximab IV
CSplenectomy
DIVIG therapy
Why Prednisolone is correct
The vignette is classic primary warm autoimmune hemolytic anemia (warm AIHA): hemolysis (high reticulocytes, LDH, and indirect bilirubin with undetectable haptoglobin) plus spherocytes and a DAT positive for IgG.
High-dose corticosteroids (prednisolone or prednisone, 1 mg/kg/day) are the guideline-defined first-line therapy, producing an initial response in roughly 70-80% of patients before a slow taper over 3-6 months once hemoglobin stabilizes.
Folic acid is added for ongoing hemolysis, and any underlying cause (lymphoproliferative disorder, SLE, drug) is sought and treated.
Why the others are wrong
Rituximab IV is an anti-CD20 monoclonal antibody and an effective therapy in warm AIHA, but it is reserved as second-line for steroid-refractory or steroid-dependent disease, not initial treatment.
Splenectomy is a historic second-line option with roughly 50-60% durable response that requires pre-procedure vaccination against encapsulated organisms; it is not appropriate before a steroid trial.
IVIG therapy is less effective in warm AIHA than in ITP and is used only as a temporizing measure in severe cases, not as guideline first-line therapy.
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IgG (sometimes IgG + complement) autoantibodies bind Rh-related red cell antigens at 37°C. Fc receptors on splenic macrophages recognize IgG-coated cells, leading to partial membrane removal (producing spherocytes) and eventual phagocytic destruction in the spleen — extravascular hemolysis. Complement activation contributes in some cases, occasionally causing intravascular hemolysis.
Clinical presentation
Symptoms
Insidious or acute fatigue, dyspnea on exertion, pallor
Jaundice, dark urine in severe cases
Constitutional symptoms if underlying lymphoma or autoimmune disease
Fever, abdominal pain in fulminant hemolysis
Signs / physical exam
Pallor with scleral icterus
Splenomegaly (variable)
Tachycardia, flow murmur
Findings of underlying disease (lymphadenopathy in CLL/NHL, rash in SLE)
Classic findings
Anemia with spherocytes on smear and a positive direct Coombs (DAT) for IgG ± C3.
Differential diagnosis
Cold agglutinin disease — IgM antibody, optimum binding at 4°C, peripheral cyanosis on cold exposure, DAT positive for complement only (C3d), often post-Mycoplasma or with lymphoma
Transfuse only for life-threatening anemia — finding compatible blood is difficult; use 'least incompatible' units, transfuse slowly, monitor closely (do not withhold if needed)
Second-line / adjunct
Rituximab — anti-CD20 monoclonal antibody; standard second-line for steroid-refractory or steroid-dependent disease; ~70-80% response
Immunosuppressants: cyclosporine, mycophenolate mofetil, azathioprine, cyclophosphamide for refractory disease
IVIG — less effective than in ITP but can be used as a temporizing measure
Fostamatinib (SYK inhibitor) — emerging evidence for warm AIHA
Newer agents: complement inhibitors (sutimlimab) primarily for cold AIHA, not warm
Complications
Venous thromboembolism — increased risk during active hemolysis (consider VTE prophylaxis)
Cardiovascular events from severe anemia
Cholelithiasis (pigment stones)
Steroid-related: hyperglycemia, osteoporosis, infection, weight gain, mood changes, avascular necrosis
Rituximab-related: infusion reactions, hepatitis B reactivation, infection
Post-splenectomy sepsis from encapsulated organisms
Relapse common; many patients require long-term immunosuppression
PANCE pearls
Positive direct Coombs (DAT) is the diagnostic hallmark — distinguishes immune from non-immune hemolysis.
Spherocytes on smear can be seen in BOTH hereditary spherocytosis AND warm AIHA — DAT differentiates (positive in AIHA, negative in HS).
Up to 10% of warm AIHA have negative DAT ('Coombs-negative AIHA') — diagnosis requires high clinical suspicion and exclusion of alternatives.
Always screen for underlying lymphoma or CLL in adults with new warm AIHA; consider age-appropriate cancer screening.
Methyldopa is the classic drug cause of warm AIHA — historical importance in board questions despite uncommon use today.
Evans syndrome = warm AIHA + immune thrombocytopenia (± immune neutropenia); higher relapse rates and often associated with underlying autoimmune disease.
Cross-matching is difficult because autoantibody reacts with all RBCs — laboratory must identify any alloantibodies separately; 'least incompatible' units used if transfusion necessary.
References
First International Consensus Meeting 2020 — Diagnosis and treatment of autoimmune hemolytic anemia in adults: Recommendations from the First International Consensus Meeting (Jäger et al., Blood Reviews 2020)
BSH 2017 — Guidelines on the management of drug-induced immune and secondary autoimmune, haemolytic anaemia (Hill et al., Br J Haematol)
Barcellini & Fattizzo — Clinical applications of hemolytic markers in the differential diagnosis and management of hemolytic anemia (Dis Markers 2015)
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