What are the differential diagnoses for a patient with suspected autoimmune hemolytic anemia?

Differential Diagnoses for Suspected Autoimmune Hemolytic Anemia

The differential diagnosis for suspected autoimmune hemolytic anemia must systematically exclude other hemolytic conditions, bone marrow disorders, infectious causes, drug-induced hemolysis, and hereditary hemoglobinopathies through targeted laboratory evaluation and clinical assessment. 1

Primary Differential Categories

Autoimmune Hemolytic Anemia Subtypes

Warm Autoimmune Hemolytic Anemia (wAIHA)

• Accounts for 80% of AIHA cases with IgG autoantibodies reactive at 37°C 2
• Direct antiglobulin test (DAT) positive for IgG, C3d, or both 2
• Reticulocyte percentage typically elevated at 14.00% (range 0.10%-55.95%) 3
• Can be primary (idiopathic) or secondary to lymphoproliferative disorders, autoimmune diseases, or infections 4

Cold Agglutinin Syndrome (CAS) and Cold Agglutinin Disease (CAD)

• IgM antibodies specific to Ii blood group system, reactive at temperatures below 37°C 2
• CAS represents polyclonal antibody production; CAD represents monoclonal production with more severe manifestations 2
• DAT positive only for C3d (IgG negative) 2
• LDH levels markedly elevated, typically >1,000 U/L in 79.1% of cases 3

Mixed AIHA

• Combined warm and cold antibody features 2
• DAT positive for both IgG and C3d 2
• Requires treatment approaches addressing both warm and cold components 2

Paroxysmal Cold Hemoglobinuria (PCH)

• Biphasic cold-reactive IgG antibody (Donath-Landsteiner antibody) recruiting complement 2
• DAT positive only for C3d 2
• Usually self-remitting, often post-viral in children 4

DAT-Negative AIHA

• IgG antibody levels below DAT detection thresholds, or non-detected IgM/IgA antibodies 2
• Represents 18.18% of AIHA cases in some series 5
• Managed as warm AIHA despite negative DAT 2

Non-Immune Hemolytic Anemias

Paroxysmal Nocturnal Hemoglobinuria (PNH)

• Reticulocyte percentage significantly lower at 6.70% (range 0.14%-22.82%) compared to AIHA 3
• LDH dramatically elevated >1,500 U/L (range 216-5,144 U/L), with 79.1% exceeding 1,000 U/L 3
• Splenomegaly present in only 43.5% of cases, with severe splenomegaly in 16.0% 3
• Hemosiderinuria typical of chronic intravascular hemolysis 6
• Requires flow cytometric analysis for CD55/CD59 deficiency 1

Hereditary Spherocytosis (HS)

• Total bilirubin markedly elevated at 79.3 μmol/L (range 11.2-244.0 μmol/L), with 64.1% exceeding 4 times upper limit of normal 3
• Reticulocyte percentage 11.83% (range 0.60%-57.39%) 3
• Splenomegaly present in 100% of cases, with severe splenomegaly in 90.4% 3
• Cholelithiasis prevalence 43.1%, significantly higher than AIHA (10.5%) or PNH (2.9%) 3
• Osmotic fragility testing and eosin-5-maleimide binding test diagnostic 6

Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency

• Hemolysis triggered by oxidant drugs, infections, or fava beans 1
• Heinz bodies visible on peripheral smear 1
• Elevated methemoglobin may occur after oxidant drug exposure 1
• G6PD enzyme assay diagnostic, but must be performed when patient not actively hemolyzing 1

Drug-Induced Hemolytic Anemia

Drug-Induced Immune Hemolytic Anemia (DIIHA)

• Appears as warm AIHA with DAT positive for IgG and/or C3d 2
• Common culprits include ribavirin, rifampin, dapsone, interferon, cephalosporins, penicillins, NSAIDs, quinine/quinidine, fludarabine, ciprofloxacin 1
• May resolve after discontinuing offending drug 2
• Requires detailed medication history including over-the-counter medications and herbals 1

Oxidant Drug-Induced Hemolysis

• Causes methemoglobinemia with cyanosis and dark brown blood 1
• Methemoglobin levels 10%-30% cause cyanosis, headaches, tachycardia, mild dyspnea 1
• Levels >70% potentially lethal 1

Thrombotic Microangiopathies

Thrombotic Thrombocytopenic Purpura (TTP) and Hemolytic Uremic Syndrome (HUS)

• Microangiopathic hemolytic anemia with schistocytes on peripheral smear 6
• Thrombocytopenia suggests possible thrombotic microangiopathy or Evans' syndrome 6
• Requires coagulation studies (PT, aPTT, fibrinogen, D-dimer) to exclude DIC 1

Disseminated Intravascular Coagulation (DIC)

• Consumption of platelets and coagulation factors through widespread fibrin deposition 1
• Elevated D-dimer, prolonged PT/aPTT, low fibrinogen 1
• Deep coagulopathy with marked INR increase 1

Infectious Causes

Viral Infections

• Hepatitis B virus reactivation: elevated AST/ALT, elevated HBV DNA, elevated HBsAg 1
• Hepatitis C: AST/ALT >400 IU/ml, elevated HCV RNA 1
• HIV: testing mandatory in all adults with suspected AIHA 1, 7
• Mycoplasma pneumoniae: can trigger cold agglutinin syndrome 1
• Epstein-Barr virus: associated with cold agglutinins 1

Bacterial Infections

• Mycoplasma: evaluation required in diagnostic work-up 1

Bone Marrow Disorders

Myelodysplastic Syndromes

• Bone marrow examination mandatory in patients >60 years to exclude 7
• Cytogenetic analysis required 1
• Reticulocytopenia may occur with marrow involvement 6

Leukemias and Lymphoproliferative Disorders

• Secondary AIHA associated with chronic lymphocytic leukemia, lymphomas 4
• Bone marrow analysis with flow cytometry and cytogenetics indicated 1

Metabolic and Hereditary Disorders

Wilson Disease

• First manifestation or consequence of abrupt discontinuation of chelation therapy 1
• High serum bilirubin >10 mg/dl (mainly indirect), Coombs-negative hemolysis 1
• AST/ALT ratio >2.2, low serum ceruloplasmin <20 mg/dl 1
• 24-hour urinary copper excretion >100 μg (usually >500 μg/24h) 1
• Leipzig Scoring System guides diagnosis 1

Hereditary Hemochromatosis

• Elevated serum iron and ferritin levels 1
• Genetic testing for HFE mutations diagnostic 1

Alpha-1 Antitrypsin Deficiency

• Normal α1-antitrypsin phenotype excludes diagnosis 1
• Partial deficiency may confound clinical picture 1

Mechanical Hemolysis

Prosthetic Valve Hemolysis

• Prosthetic valve replacement and stenting associated with intravascular and chronic hemolysis 6
• Marked LDH elevation and hemosiderinuria 6

Ischemic Hepatitis

• High peak AST/ALT (usually >1,000 IU/ml), serum bilirubin usually <3 mg/dl 1
• Deep coagulopathy with marked INR increase that improves rapidly 1
• Abdominal ultrasonography must confirm vascular patency 1

Essential Diagnostic Algorithm

Initial Laboratory Evaluation

Complete Blood Count and Peripheral Smear

• CBC with differential to identify isolated anemia versus pancytopenia 7
• Peripheral smear examination mandatory to exclude pseudothrombocytopenia, identify schistocytes, spherocytes, Heinz bodies 1, 6
• Reticulocyte count: elevated in compensated hemolysis, but reticulocytopenia occurs in 20-40% of AIHA cases (poor prognostic factor) 6

Hemolysis Markers

• Lactate dehydrogenase (LDH): elevated in intravascular hemolysis, markedly increased (>1,000 U/L) suggests PNH over AIHA 6, 3
• Haptoglobin: reduced in hemolysis 6
• Unconjugated (indirect) bilirubin: elevated 6
• Direct antiglobulin test (DAT): cornerstone of autoimmune diagnosis 6

Coagulation Studies

• PT, aPTT, fibrinogen, D-dimer to evaluate for DIC 1

Immunohematologic Testing

Direct Antiglobulin Test (DAT)

• Positive for IgG and/or C3d in warm AIHA 2
• Positive only for C3d in cold agglutinin disease and PCH 2
• Negative in DAT-negative AIHA (requires high index of suspicion) 2

Autoimmune Serology

• ANA, anti-smooth muscle antibodies to evaluate for autoimmune hepatitis overlap 1
• Anti-LKM1 antibodies in type 2 autoimmune hepatitis 1

Infectious Disease Screening

Mandatory Testing

• HIV testing in all adults with suspected AIHA 1, 7
• Hepatitis C virus testing in all adults 1, 7
• Hepatitis B surface antigen, HBV DNA if reactivation suspected 1
• H. pylori screening (eradication may resolve thrombocytopenia in associated cases) 7

Specialized Testing Based on Clinical Suspicion

For PNH

• Flow cytometry for CD55/CD59 deficiency on red cells and granulocytes 1
• Hemosiderinuria assessment 6

For Hereditary Spherocytosis

• Osmotic fragility testing 6
• Eosin-5-maleimide binding test 6
• Family history assessment 3

For G6PD Deficiency

• G6PD enzyme assay (perform when not actively hemolyzing) 1
• Heinz body preparation 1

For Wilson Disease

• Serum ceruloplasmin, 24-hour urinary copper 1
• Slit-lamp examination for Kayser-Fleischer rings 1
• Leipzig Scoring System application 1

For Methemoglobinemia

• Methemoglobin level by co-oximetry 1
• Cytochrome b5 reductase enzymatic activity 1
• DNA analysis for CYB5R3 mutations 1

Bone Marrow Examination Indications

Mandatory Bone Marrow Evaluation

• Age >60 years to exclude myelodysplastic syndromes, leukemias 7
• Systemic symptoms (fever, weight loss, bone pain) 7
• Abnormal blood count parameters beyond isolated anemia 7
• Atypical peripheral smear findings 7
• Reticulocytopenia despite hemolysis 6
• Consideration of splenectomy 7

Critical Diagnostic Pitfalls

Reticulocytopenia in AIHA

• Occurs in 20-40% of AIHA cases due to marrow involvement, iron/vitamin deficiency, infections, or autoimmune reaction against bone marrow precursors 6
• Represents poor prognostic factor 6
• Do not exclude AIHA based on low reticulocyte count alone 6

Confounding Laboratory Findings

• Increased reticulocytes, LDH, and bilirubin occur in conditions other than hemolysis (ineffective erythropoiesis, liver disease) 6
• Reduced haptoglobin may occur in liver disease independent of hemolysis 6

Missing Secondary Causes

• Failing to test for HIV, HCV in all adults with suspected AIHA leads to missed secondary causes with different treatment approaches 7
• Not evaluating for underlying lymphoproliferative disorders in older patients 4

Drug History Inadequacy

• Incomplete medication history missing over-the-counter medications, herbals, and supplements 1
• Not considering recent medication changes within 1-2 weeks of symptom onset 1