How do you diagnose hemolysis?

Diagnosing Hemolysis: Laboratory and Clinical Approach

The diagnosis of hemolysis requires a comprehensive laboratory workup including reticulocyte count, lactate dehydrogenase (LDH), haptoglobin, unconjugated bilirubin, and peripheral blood smear examination. 1

Primary Diagnostic Tests for Hemolysis

Essential Laboratory Parameters

• Complete blood count (CBC) with red cell indices
• Reticulocyte count - typically elevated in hemolysis (compensatory response)
• Lactate dehydrogenase (LDH) - elevated in hemolysis, especially intravascular
• Haptoglobin - reduced or absent in hemolysis
• Unconjugated bilirubin - elevated in hemolysis
• Peripheral blood smear - to identify abnormal red cell morphologies

Interpretation of Key Markers

1. Reticulocytosis: Indicates bone marrow's compensatory response to hemolysis

   • May be inadequate/absent in 20-40% of cases due to:
     • Bone marrow involvement
     • Iron/vitamin deficiency
     • Infections
     • Autoimmune reaction against marrow precursors 1

2. Haptoglobin:

   • Decreased or absent in both intravascular and extravascular hemolysis
   • Most sensitive marker for ongoing hemolysis

3. LDH:

   • Markedly elevated in intravascular hemolysis
   • Moderately elevated in extravascular hemolysis

4. Unconjugated bilirubin:

   • Elevated due to increased red cell breakdown
   • Usually <5 mg/dL in chronic hemolysis 1

Additional Tests Based on Clinical Suspicion

For Immune-Mediated Hemolysis

• Direct antiglobulin test (DAT/Coombs test) - cornerstone for diagnosing autoimmune hemolytic anemia 1
• Autoimmune serology - to identify underlying autoimmune disorders

For Intravascular Hemolysis

• Hemoglobinuria - free hemoglobin in urine
• Hemosiderinuria - iron deposits in urine
• Free hemoglobin in plasma

For Specific Etiologies

• Glucose-6-phosphate dehydrogenase (G6PD) screening - for enzymopathies
• Hemoglobin electrophoresis - for hemoglobinopathies
• Osmotic fragility test - for membrane disorders like hereditary spherocytosis

Differential Diagnosis Based on Laboratory Findings

Intravascular vs. Extravascular Hemolysis

• Intravascular hemolysis:

  • Markedly elevated LDH
  • Hemoglobinemia and hemoglobinuria
  • Hemosiderinuria
  • Severely reduced or absent haptoglobin

• Extravascular hemolysis:

  • Moderately elevated LDH
  • No hemoglobinemia or hemoglobinuria
  • Reduced haptoglobin
  • Increased unconjugated bilirubin

Red Cell Morphology Clues

• Spherocytes: Immune hemolysis, hereditary spherocytosis
• Schistocytes: Microangiopathic hemolytic anemia, thrombotic thrombocytopenic purpura
• Bite cells: Oxidative hemolysis (G6PD deficiency)
• Echinocytes: PK deficiency (especially post-splenectomy) 1

Common Pitfalls and Caveats

1. False normal haptoglobin levels despite hemolysis in:

   • Inflammatory conditions (haptoglobin is an acute phase reactant)
   • Liver disease (increased production)

2. Elevated LDH without hemolysis in:

   • Liver disease
   • Myocardial infarction
   • Malignancies

3. Reticulocytosis without hemolysis in:

   • Recovery from blood loss
   • Recovery from vitamin B12/folate deficiency treatment

4. Falsely normal reticulocyte count in hemolysis with:

   • Iron deficiency
   • Folate deficiency
   • Bone marrow suppression

5. Transfusion interference:

   • Recent transfusions can mask hemolysis markers
   • PK enzyme activity may appear normal due to donor cells 1

Algorithmic Approach to Suspected Hemolysis

1. First-line tests: CBC, reticulocyte count, LDH, haptoglobin, bilirubin, peripheral blood smear
2. If hemolysis confirmed: Proceed to DAT to differentiate immune vs. non-immune causes
3. If DAT positive: Evaluate for autoimmune hemolytic anemia, drug-induced hemolysis
4. If DAT negative: Evaluate for:
   • Membrane disorders (blood smear, osmotic fragility)
   • Enzymopathies (G6PD, PK assays)
   • Hemoglobinopathies (hemoglobin electrophoresis)
   • Mechanical hemolysis (schistocytes on smear)
   • Infectious causes (blood smear, specific tests)

Remember that hemolysis can be a manifestation of various underlying conditions, and identifying the cause is crucial for appropriate management and prevention of complications.