What are the diagnostic tests for hemolysis (breakdown of red blood cells)?

From the Guidelines

Hemolysis can be detected through several laboratory tests, with the most essential tests including complete blood count (CBC) with peripheral blood smear, reticulocyte count, lactate dehydrogenase (LDH), haptoglobin, and direct and indirect bilirubin levels, as recommended by recent studies 1. To evaluate hemolysis, the following tests are helpful:

• Complete blood count (CBC) with peripheral blood smear to identify decreased hemoglobin and hematocrit with elevated reticulocytes, suggesting active hemolysis
• Reticulocyte count to assess the bone marrow's response to hemolysis
• Lactate dehydrogenase (LDH) to detect elevated levels released from damaged red cells
• Haptoglobin to identify decreased or absent levels due to saturation with free hemoglobin
• Direct and indirect bilirubin levels to evaluate the increase in indirect (unconjugated) bilirubin as hemoglobin breaks down Additional tests may include:
• Direct antiglobulin test (Coombs test) to detect immune-mediated hemolysis
• Hemoglobinuria testing
• Specific tests for hereditary conditions like G6PD deficiency or hereditary spherocytosis
• Evaluation for viral or bacterial causes of hemolysis, such as mycoplasma
• Protein electrophoresis and cryoglobulin analysis
• Glucose-6-phosphate dehydrogenase level
• Assessment of methemoglobinemia It is essential to consider the clinical presentation, family history, and time of last blood transfusion when interpreting test results, as recommended by studies 1. In cases of genotype discrepancies or suspected pyruvate kinase deficiency, further investigation with assays for detection of large deletions, re-evaluation of other causes of hemolysis by specific tests or NGS platform, and molecular testing of the PKLR gene may be necessary, as suggested by studies 1.

From the Research

Tests for Hemolysis

• Laboratory tests that confirm hemolysis include:
  • Reticulocytosis 2, 3
  • Increased lactate dehydrogenase 2, 3
  • Increased unconjugated bilirubin 2, 3
  • Decreased haptoglobin levels 2, 3
• The direct antiglobulin test (DAT) is used to differentiate immune causes from nonimmune causes of hemolysis 2, 3
• A peripheral blood smear should be performed to identify abnormal red blood cell morphologies 2

Classification of Hemolytic Diseases

• Hemolytic diseases are classified into:
  • Hemoglobinopathies 2
  • Membranopathies 2
  • Enzymopathies 2
  • Immune-mediated anemias 2
  • Extrinsic nonimmune causes 2

Approach to Haemolysis

• Subdividing patients into those who are 'direct antiglobulin test (DAT) positive' (immune) or 'DAT negative' (non-immune) is a simple and clinically relevant way to start to formulate a cause for the haemolytic anaemia 3
• Immune causes of haemolytic anaemia include autoimmune haemolytic anaemia, drugs and delayed haemolytic transfusion reactions 3
• Non-immune causes include the haemoglobinopathies (such as sickle cell disease) and microangiopathic haemolytic anaemias (such as disseminated intravascular coagulation) 3

Complete Blood Count

• The complete blood count is one of the most frequently ordered laboratory tests in medicine 4
• The components of the complete blood count include:
  • Red blood cell count
  • Hemoglobin
  • Hematocrit
  • Red blood cell indices
  • Reticulocyte count
  • White blood cell count and differential
  • Platelet count 4