What are hemolysis labs?

Hemolysis Laboratory Testing

Hemolysis labs are a panel of laboratory tests used to confirm red blood cell destruction and include: reticulocyte count, lactate dehydrogenase (LDH), unconjugated bilirubin, haptoglobin, peripheral blood smear, and direct antiglobulin test (DAT/Coombs). 1

Core Hemolysis Markers

The essential laboratory tests that confirm hemolysis include:

• Reticulocyte count (elevated): Indicates increased bone marrow production in response to red cell destruction; typically >3-5% in hemolytic conditions 2, 1
• Lactate dehydrogenase (LDH) (elevated): Released from lysed red blood cells; serves as a sensitive marker of hemolysis 2, 1
• Unconjugated (indirect) bilirubin (elevated): Results from breakdown of heme from destroyed red cells 1, 3
• Haptoglobin (decreased): Binds free hemoglobin and becomes depleted during hemolysis 2, 1
• Peripheral blood smear: Essential for identifying abnormal red blood cell morphologies that suggest specific hemolytic disorders 1

Distinguishing Immune from Non-Immune Hemolysis

The direct antiglobulin test (DAT/Coombs test) is the critical step that differentiates immune-mediated from non-immune causes of hemolysis. 2, 4

• A positive DAT indicates antibodies or complement on red cell surfaces, suggesting immune-mediated hemolysis 4
• A negative DAT points toward non-immune causes such as membrane defects, enzyme deficiencies, or mechanical destruction 4

Additional Markers for Severe Intravascular Hemolysis

When intravascular hemolysis is severe and rapid, additional findings include:

• Free hemoglobin (elevated): Indicates direct lysis of red cells in circulation 3
• Hemoglobinuria: Visible when hemoglobin exceeds renal threshold 1, 3
• Hemosiderinuria: Indicates chronic intravascular hemolysis 3
• Hemopexin (decreased): Binds free heme and becomes depleted 3

Complete Initial Workup

For suspected hemolysis, the comprehensive initial laboratory panel should include:

• Complete blood count (CBC) with differential: Assesses degree of anemia and white blood cell abnormalities 2, 5
• Reticulocyte count: Confirms bone marrow response 2, 1
• Fractionated bilirubin: Confirms predominantly unconjugated hyperbilirubinemia 2
• LDH and haptoglobin: Core hemolysis markers 2, 1
• Peripheral blood smear: Identifies specific red cell morphologies 1
• Direct antiglobulin test (DAT): Differentiates immune from non-immune causes 2, 4

Critical Preanalytical Considerations

Proper specimen handling is crucial to avoid in vitro hemolysis, which can cause spurious results in over 60% of cases. 2, 6

• Use a straight needle rather than butterfly to minimize hemolysis during collection 2
• Avoid tourniquet pressure during collection 2
• Process samples within 1 hour at room temperature 2
• Visibly hemolyzed samples should be rejected as they cause spurious results 2, 6
• Hemolysis accounts for over 60% of blood sample rejections in laboratories 6

Common Pitfalls

• Mistaking Gilbert syndrome for hemolysis: Can cause isolated unconjugated hyperbilirubinemia without actual hemolysis 2
• False DAT results: May occur with improper washing, centrifugation, or specimen agitation 4
• Reticulocytosis without hemolysis: Can occur with recent blood loss or response to treatment 1
• Normal haptoglobin despite hemolysis: Haptoglobin is an acute phase reactant and may be falsely elevated in inflammatory states 1

Second-Line Testing Based on Initial Results

If initial hemolysis labs are positive but etiology unclear:

• G6PD enzyme assay: For suspected enzyme deficiency, especially in patients of African, Mediterranean, or Asian descent 2
• Hemoglobin electrophoresis: For suspected hemoglobinopathies or thalassemia 5
• Osmotic fragility or eosin-5-maleimide (EMA) binding test: For suspected membrane defects 7
• Blood typing and antibody screen: For immune-mediated hemolysis 2