Autoimmune hemolytic anemia is an acquired condition in which autoantibodies target red blood cell surface antigens, leading to premature RBC destruction. It is classified by antibody thermal reactivity: warm AIHA (60–70% of cases, IgG-mediated, extravascular hemolysis) and cold agglutinin disease (20–25%, IgM-mediated, complement-driven intravascular hemolysis), with rarer mixed and paroxysmal cold hemoglobinuria subtypes. [1-2] Incidence is approximately 0.8–3 per 100,000/year, and ~50% of warm AIHA cases are secondary to an underlying condition. [3-4]
The following diagnostic algorithm from the NEJM provides a systematic approach to AIHA subtype classification:
1. History
- Onset and tempo of symptoms: acute vs. insidious fatigue, exertional dyspnea, palpitations [3]
- Dark or "soy sauce-colored" urine (hemoglobinuria) — suggests intravascular hemolysis [6]
- Jaundice — timing and progression
- Cold-triggered symptoms: acrocyanosis, Raynaud-like phenomena, worsening with cold exposure (suggests cold AIHA) [3]
- Recent infections (viral illness, Mycoplasma, EBV — triggers for cold agglutinin syndrome; SARS-CoV-2) [4-5]
- Medication history: recent antibiotics (cephalosporins, piperacillin), checkpoint inhibitors, fludarabine, NSAIDs [5]
- Prior blood transfusions and any transfusion reactions
- History of autoimmune disease (SLE, RA, scleroderma) or lymphoproliferative disorder (CLL, NHL) [3]
- Prior episodes of anemia or hemolysis; chronicity and relapsing pattern [2]
2. Alarm Features
- Hemoglobin <6 g/dL — requires emergent transfusion [3]
- Brisk intravascular hemolysis with chest pain, lethargy, confusion — medical emergency [3]
- Tachycardia, hypotension, or signs of cardiovascular decompensation
- Rapidly dropping hemoglobin unresponsive to transfusion [7]
- Dark urine (hemoglobinuria) with hyperkalemia — risk of renal injury
- Concurrent thrombocytopenia (Evans syndrome) — raises concern for TTP/HUS overlap or underlying immunodeficiency [8]
- Venous thromboembolism: absolute risk of VTE is 15–30% in warm AIHA [3]
3. Medications
- Causative agents: ceftriaxone, other cephalosporins, piperacillin, NSAIDs, penicillins, fludarabine, checkpoint inhibitors (PD-1 inhibitors), methyldopa [5]
- First-line treatment: Prednisone 1 mg/kg/day (60–100 mg/day); ~80% initial response rate but only 30–40% sustained remission at 1 year [5]
- Second-line: Rituximab 375 mg/m² weekly × 4 cycles or 1000 mg × 2 doses (2-week interval); 70–80% response rate [3][5]
- IVIG: Consider in severe cases not responding within 7 days, or as bridge therapy [8]
- Prophylactic anticoagulation: Recommended during severe hemolysis given high VTE risk [2-3]
- Folic acid supplementation: Standard supportive measure given increased RBC turnover [4]
- Recombinant erythropoietin: When reticulocytopenia or inadequate marrow compensation is present [2]
- Cold AIHA: Steroids are largely ineffective chronically; rituximab is first-line; sutimlimab (anti-C1s complement inhibitor) is FDA-approved for hemolysis in cold agglutinin disease [9-10]
- Contraindicated/caution: Avoid fludarabine monotherapy in CLL patients (exacerbates AIHA); avoid cold exposure in cold AIHA [3][5]
4. Diet
- No specific dietary triggers for AIHA
- Folic acid-rich foods (leafy greens, legumes) to support erythropoiesis
- Adequate hydration, especially during brisk hemolysis, to maintain renal perfusion and urine output
- Iron supplementation is generally not indicated unless concurrent iron deficiency is documented (hemolysis itself does not cause iron loss unless significant hemoglobinuria)
5. Review of Systems
- Constitutional: Fatigue, malaise, fever (may suggest underlying infection or lymphoma)
- HEENT: Scleral icterus, pallor of conjunctivae/mucous membranes
- Cardiovascular: Dyspnea on exertion, palpitations, chest pain, peripheral edema [3]
- GI: Abdominal pain (splenic infarction/congestion), dark urine, change in stool color
- Musculoskeletal: Joint pain (SLE, RA as secondary causes)
- Skin: Rash (lupus), acrocyanosis or livedo reticularis (cold AIHA), petechiae (Evans syndrome)
- Neurologic: Confusion, lethargy (severe anemia or brisk hemolysis) [3]
- Lymphatic: Lymphadenopathy, night sweats, weight loss (lymphoproliferative disease)
6. Collateral History and Family History
- Family history of autoimmune diseases (SLE, thyroid disease, other cytopenias)
- Family history of hereditary hemolytic anemias (spherocytosis, G6PD deficiency) to exclude mimics
- History of autoimmune lymphoproliferative syndrome (ALPS) — germline FAS, FASL, CASP10 mutations predispose to AIHA [3]
- Common variable immunodeficiency (CVID) — associated with AIHA [3]
- Social history: occupational cold exposure (relevant for cold AIHA), HIV risk factors
7. Risk Factors
- Autoimmune diseases: SLE, rheumatoid arthritis, scleroderma [3]
- Lymphoproliferative disorders: CLL, non-Hodgkin lymphoma, Hodgkin lymphoma [3][5]
- Immunodeficiency: CVID, ALPS, post-transplant (HSCT or solid organ) [3]
- Infections: HIV, EBV, Mycoplasma pneumoniae, SARS-CoV-2, babesiosis (especially post-splenectomy) [3][5]
- Medications: Checkpoint inhibitors, cephalosporins, fludarabine, piperacillin [5]
- Age: More common after age 50; bimodal distribution in some series [4]
- Monoclonal gammopathy: Present in >20% of warm AIHA patients, more than 5× the expected rate [3]
8. Differential Diagnosis
- Thrombotic thrombocytopenic purpura (TTP) / Hemolytic uremic syndrome (HUS): Schistocytes on smear, thrombocytopenia, renal failure; DAT-negative
- Paroxysmal nocturnal hemoglobinuria (PNH): Flow cytometry for GPI-anchored proteins; DAT-negative
- Hereditary spherocytosis: Family history, osmotic fragility test; DAT-negative
- G6PD deficiency: Oxidative stress triggers, bite cells/Heinz bodies; DAT-negative
- Drug-induced hemolytic anemia: Temporal relationship with offending drug; may be DAT-positive [5]
- Delayed hemolytic transfusion reaction: Recent transfusion history; DAT-positive with alloantibody
- Microangiopathic hemolytic anemia (MAHA/DIC): Schistocytes, abnormal coagulation panel; DAT-negative [11]
- Sickle cell disease / Hemoglobinopathies: Hemoglobin electrophoresis
- Evans syndrome: AIHA + immune thrombocytopenia ± autoimmune neutropenia [8]
Key distinguishing feature: A positive DAT strongly supports AIHA over non-immune causes, though DAT-negative AIHA occurs in 3–10% of cases. [5]
9. Past Medical History
- Prior episodes of hemolytic anemia or documented AIHA (relapsing course is common)
- Known autoimmune conditions (SLE, thyroiditis, inflammatory bowel disease)
- Lymphoproliferative disorders or prior chemotherapy
- Prior splenectomy (affects management options and increases babesiosis risk)
- History of VTE (AIHA independently increases thrombotic risk) [3]
- Transfusion history and known alloantibodies
- Immunodeficiency syndromes
10. Physical Exam
- Vital signs: Tachycardia, tachypnea, hypotension (in severe/acute hemolysis)
- General: Pallor, jaundice/icterus proportional to severity [3]
- HEENT: Scleral icterus, conjunctival pallor
- Cardiovascular: Flow murmur, elevated JVP, peripheral edema (high-output failure) [3]
- Abdomen: Splenomegaly (especially with underlying lymphoproliferative disease); hepatomegaly [3]
- Skin: Acrocyanosis, livedo reticularis (cold AIHA); petechiae/purpura (Evans syndrome); rash (SLE)
- Lymph nodes: Lymphadenopathy (suggests lymphoma, CLL, or infection)
- Extremities: Peripheral cyanosis with cold exposure (cold agglutinin disease)
11. Lab Studies
Pearl: A negative DAT does not rule out AIHA — occurs in 3–10% of cases. Consider monospecific DAT (including anti-IgA) and more sensitive methods (flow cytometry DAT) if clinical suspicion is high. [5][10]
12. Imaging
- CT chest/abdomen/pelvis: Indicated to evaluate for lymphadenopathy, splenomegaly, or underlying lymphoproliferative/solid malignancy as a secondary cause [5]
- Ultrasound abdomen: Can assess splenomegaly and hepatomegaly
- Imaging is not required for diagnosis of AIHA itself but is important for identifying secondary causes
- Chest imaging if VTE is suspected (CT pulmonary angiography) given the 15–30% VTE risk [3]
13. Special Tests
- Donath-Landsteiner test: Detects biphasic IgG autoantibody in paroxysmal cold hemoglobinuria (mainly in children) [5]
- Flow cytometry (peripheral blood): Screen for CLL, lymphoma, or PNH [5]
- Bone marrow biopsy: Indicated in cold agglutinin disease (to identify clonal B-cell disorder); in warm AIHA if treatment fails or bone marrow disorder is suspected [5]
- Immunoglobulin quantification: Detect CVID (hypogammaglobulinemia) or monoclonal gammopathy [5]
- Viral serologies: HIV, hepatitis B/C, EBV, CMV as clinically indicated
- ANA, dsDNA, complement levels: If SLE or other connective tissue disease is suspected
- ADAMTS13 activity: If TTP is in the differential (thrombocytopenia + MAHA)
14. ECG
- Indications: Severe anemia (Hb <7 g/dL), chest pain, tachycardia, elderly patients, known cardiac disease
- Expected findings: Sinus tachycardia, ST-T wave changes from demand ischemia
- Dangerous patterns: ST elevation or depression suggesting ACS in the setting of severe anemia; new arrhythmias
- Continuous telemetry monitoring warranted in hemodynamically significant anemia
15. Assessment
Severity stratification: [2][5]
- Mild/compensated: Hemoglobin near normal, reticulocytosis compensates for hemolysis, minimal symptoms
- Moderate: Hb 8–10 g/dL, symptomatic fatigue/dyspnea, requires treatment
- Severe: Hb <8 g/dL — international consensus recommends adding rituximab to steroids upfront [5]
- Life-threatening: Hb <6 g/dL, hemodynamic instability, brisk intravascular hemolysis with chest pain/confusion — medical emergency [3]
Warm AIHA carries a mortality rate of up to 22% and has a chronic, relapsing course. [7] More than 50% of patients require blood transfusion at presentation. [3] Always evaluate for secondary causes, as ~50% of warm AIHA is associated with an underlying condition. [3][5]
16. Treatment Plan
Initial Stabilization (ED/Acute)
- Transfuse ABO- and RhD-matched blood if Hb <6 g/dL; goal Hb >7 g/dL. Do not withhold transfusion due to crossmatch difficulties — "least incompatible" blood is acceptable in emergencies [3]
- Monitor for transfusion reactions (fever, chills, worsening hemoglobinuria) [3]
- Check potassium (hemolysis-related hyperkalemia) [7]
Warm AIHA — First-Line [2][5]
- Prednisone 1 mg/kg/day (60–100 mg/day) for 2–3 weeks, then taper over 3–6 months
- Add rituximab upfront if Hb <8 g/dL (severe disease) — two RCTs showed doubling of long-term responses with combination therapy [5]
- IVIG if no response within 7 days and severe anemia [8]
- Prophylactic anticoagulation during active severe hemolysis [2]
- Folic acid 1 mg daily
Warm AIHA — Second-Line [3][5]
- Rituximab (if not given first-line): 375 mg/m² weekly × 4 or 1000 mg × 2 doses
- Response in 70–80%, but ~30% relapse within 3 years
Warm AIHA — Third-Line and Beyond [3][5]
- Splenectomy (~70% response, but infection/thrombosis risks; increasingly deferred)
- Immunosuppressants: mycophenolate mofetil, azathioprine, cyclosporine, cyclophosphamide
- Emerging agents: fostamatinib, rilzabrutinib, nipocalimab, sovleplenib [2][13]
Cold Agglutinin Disease [10]
- Avoid cold exposure
- Steroids are largely ineffective long-term
- Rituximab is first-line for treatment-requiring CAD
- Sutimlimab (Enjaymo, anti-C1s) — FDA-approved for hemolysis in CAD [9]
- Rituximab + bendamustine for refractory cases
Emergency/Refractory [5]
- High-dose IV methylprednisolone, IVIG, plasma exchange
- Complement C1 inhibition
- Bortezomib + dexamethasone in refractory cases
17. Disposition
- Admit: Hb <7 g/dL, hemodynamic instability, brisk intravascular hemolysis, need for transfusion, new diagnosis requiring workup, severe symptoms (chest pain, confusion, dyspnea at rest) [3][7]
- Observation: Moderate anemia (Hb 7–10 g/dL) with active hemolysis, pending response to initial steroids
- Discharge: Stable hemoglobin, mild/compensated hemolysis, established diagnosis with outpatient hematology follow-up arranged, reliable patient
- Hematology consultation: All new diagnoses of AIHA; urgent for severe or refractory cases [12]
- Consider ICU: Life-threatening anemia (Hb <5 g/dL), hemodynamic compromise, multiorgan dysfunction
18. Follow Up / Return Precautions
- Follow-up timing: Hematology within 1–2 weeks of discharge; CBC and hemolysis labs (LDH, haptoglobin, reticulocyte count, bilirubin) at each visit [3]
- Steroid taper monitoring: Reassess response at 2–3 weeks; taper over 3–6 months; monitor for steroid side effects (glucose, blood pressure, bone density) [5]
- Monitor for VTE: Counsel on symptoms of DVT/PE; consider prophylactic anticoagulation during active hemolysis [3]
- Return precautions: Worsening fatigue, dyspnea at rest, chest pain, dark urine, fever, new bleeding or bruising (Evans syndrome), syncope
- Long-term counseling: AIHA is often a chronic, relapsing condition; additional therapies may be needed. Workup for secondary causes should be completed once stable [3][5]
- Expected course: Initial steroid response in ~80%, but sustained remission in only 30–40% at 1 year; relapse is common and should not be unexpected [5]
- Vaccinations: If splenectomy is planned, ensure pneumococcal, meningococcal, and Haemophilus influenzae type b vaccines are administered ≥2 weeks prior [5]
References
1. Autoimmune Haemolytic Anaemias. — Michel M, Crickx E, Fattizzo B, Barcellini W. Nature Reviews. Disease Primers. 2024.
2. Management of Autoimmune Hemolytic Anemia. — Barcellini W, Fattizzo B. Hematology. American Society of Hematology. Education Program. 2025.
3. Warm Autoimmune Hemolytic Anemia. — Brodsky RA. The New England Journal of Medicine. 2019.
4. Disease-Modifying Treatments for Primary Autoimmune Haemolytic Anaemia. — Liu AP, Cheuk DK. The Cochrane Database of Systematic Reviews. 2021.
5. Autoimmune Hemolytic Anemias. — Berentsen S, Barcellini W. The New England Journal of Medicine. 2021.
6. Case Report: Severe Autoimmune Hemolytic Anemia in an Elderly Patient Caused by Warm-Reactive IgG and IgA Autoantibodies. — Xia W, Lu J, Hou J, et al. Frontiers in Immunology. 2025.
7. Hematologic Emergencies: Recognition and Initial Management. — Jones DE, Walker JJ, Abellada AMP. American Family Physician. 2024.
8. Diagnosis and Management of Evans Syndrome in Adults: First Consensus Recommendations. — Fattizzo B, Marchetti M, Michel M, et al. The Lancet. Haematology. 2024.
9. FDA Orange Book. — FDA Orange Book. 2026.
10. Autoimmune Hemolytic Anemia: New Frontiers in Diagnosis and Therapy. — Barcellini W, Fattizzo B. Blood Reviews. 2026.
11. Hemolytic Anemia: Evaluation and Differential Diagnosis. — Phillips J, Henderson AC. American Family Physician. 2018.
12. Management of Immune Checkpoint Inhibitor-Related Toxicities. — Updated 2025-10-23. National Comprehensive Cancer Network.
13. Sovleplenib in Patients With Primary or Secondary Warm Autoimmune Haemolytic Anaemia: Results From Phase 2 of a Randomised, Double-Blind, Placebo-Controlled, Phase 2/3 Study. — Zhao X, Sun J, Zhang Z, et al. The Lancet. Haematology. 2025.