What labs should be ordered to evaluate hemolysis in a patient with anemia?

Laboratory Tests for Evaluating Hemolysis in Anemia Patients

The essential laboratory tests for evaluating hemolysis in anemia patients include complete blood count with reticulocyte count, lactate dehydrogenase (LDH), haptoglobin, bilirubin (total and indirect), peripheral blood smear examination, and direct antiglobulin test (Coombs test). These tests provide a comprehensive assessment of hemolytic processes and help differentiate between various causes of anemia.

Primary Hemolysis Laboratory Panel

First-line Tests

• Complete Blood Count (CBC) with differential 1, 2

  • Hemoglobin and hematocrit (to confirm anemia)
  • Red cell indices (MCV, MCH, MCHC)
  • Red cell distribution width (RDW)
  • White blood cell count and platelet count

• Reticulocyte Count 1, 3

  • Elevated in hemolytic anemia (compensatory response)
  • Helps differentiate between hemolytic and non-hemolytic causes

• Markers of Hemolysis 1, 2, 3

  • Lactate dehydrogenase (LDH) - elevated in hemolysis
  • Haptoglobin - decreased or absent in hemolysis
  • Bilirubin - elevated unconjugated (indirect) bilirubin
  • Peripheral blood smear - to evaluate red cell morphology

• Direct Antiglobulin Test (DAT/Coombs test) 2, 4

  • Essential to differentiate immune-mediated from non-immune hemolysis

Secondary and Confirmatory Tests

• Iron Studies 1, 2

  • Serum ferritin
  • Transferrin saturation (TSAT)
  • Serum iron
  • Total iron-binding capacity (TIBC)

• Hemoglobin Electrophoresis 2

  • For suspected hemoglobinopathies

• Specialized Tests Based on Clinical Suspicion

  • Red cell enzyme assays (e.g., G6PD, pyruvate kinase) 1
  • Osmotic fragility test (for hereditary spherocytosis)
  • Flow cytometry (for paroxysmal nocturnal hemoglobinuria)
  • Erythrocyte adenylate kinase (EAK) - highly sensitive and specific for hemolysis 5

Interpretation of Results

Diagnostic Patterns in Hemolytic Anemia

1. Classic Hemolysis Pattern:

   • Decreased hemoglobin
   • Elevated reticulocyte count
   • Elevated LDH
   • Decreased haptoglobin
   • Elevated indirect bilirubin

2. Important Diagnostic Considerations:

   • Normal LDH does not exclude hemolysis (present in up to 25% of autoimmune hemolytic anemia cases) 6
   • Haptoglobin may be falsely normal in concurrent inflammatory conditions
   • Reticulocytosis may be blunted in cases with bone marrow suppression

Differential Diagnosis Based on Laboratory Findings

Parameter	Iron Deficiency	Anemia of Chronic Disease	Hemolytic Anemia	Thalassemia
MCV	Low	Low or normal	Normal or high	Very low
Reticulocytes	Normal or low	Normal or low	Elevated	Normal or elevated
Serum Ferritin	Low	Normal or high	Normal	Normal
LDH	Normal	Normal	Elevated	Normal
Haptoglobin	Normal	Normal	Decreased	Normal
Bilirubin	Normal	Normal	Elevated (indirect)	Normal or slightly elevated

Special Considerations

• Intravascular vs. Extravascular Hemolysis:

  • Intravascular: Hemoglobinemia, hemoglobinuria, and hemosiderinuria may be present 7
  • Extravascular: More common; typically shows indirect hyperbilirubinemia without hemoglobinuria

• Timing of Laboratory Testing:

  • Obtain samples before blood transfusions when possible
  • Serial measurements may be necessary to detect intermittent hemolysis

• Common Pitfalls:

  • Relying solely on a single test (e.g., LDH) to diagnose or exclude hemolysis 6
  • Failing to consider inflammatory conditions that may affect haptoglobin levels
  • Not accounting for recent transfusions when interpreting results
  • Overlooking drug-induced hemolysis as a potential cause

By systematically evaluating these laboratory parameters, clinicians can effectively diagnose hemolytic anemia and determine its underlying cause, leading to appropriate management strategies that address both the anemia and its etiology.