Laboratory Markers of Hemolysis
The essential laboratory tests that suggest hemolysis include elevated LDH, decreased haptoglobin, elevated unconjugated (indirect) bilirubin, elevated reticulocyte count, and evidence of hemolysis on peripheral blood smear. 1, 2, 3
Core Laboratory Panel for Suspected Hemolysis
When evaluating for hemolysis, obtain the following tests simultaneously to establish the diagnosis:
Primary Hemolysis Markers
Lactate dehydrogenase (LDH): Elevated in hemolysis due to release from damaged red blood cells; particularly elevated in intravascular hemolysis 1, 2, 4, 5
Haptoglobin: Decreased or undetectable in hemolysis as it binds free hemoglobin released from lysed red cells 1, 2, 3, 4, 5
Unconjugated (indirect) bilirubin: Elevated due to breakdown of hemoglobin from destroyed red blood cells 1, 2, 3, 4, 5
Reticulocyte count: Typically elevated, reflecting compensatory bone marrow response to anemia 1, 2, 3, 4, 5
Essential Supporting Tests
Complete blood count (CBC) with indices: Reveals anemia, often normocytic or macrocytic, and provides baseline hemoglobin 1, 2, 3, 4
Peripheral blood smear: Critical for identifying abnormal red cell morphology such as schistocytes (microangiopathic hemolysis), spherocytes (hereditary spherocytosis or immune hemolysis), or other diagnostic features 1, 2, 3, 4
Direct antiglobulin test (DAT/Coombs test): Differentiates immune-mediated from non-immune causes of hemolysis 1, 2, 3, 4
Additional Markers for Specific Situations
Intravascular Hemolysis Indicators
Free hemoglobin in serum or plasma: Markedly elevated in intravascular hemolysis 1
Hemosiderinuria: Indicates chronic intravascular hemolysis 5
Hyperferritinemia: Associated with chronic hemolysis 5
Comprehensive Workup When Diagnosis Unclear
Disseminated intravascular coagulation (DIC) panel: Including PT/INR to exclude consumptive coagulopathy 1
Autoimmune serology: When immune-mediated hemolysis suspected 1
Paroxysmal nocturnal hemoglobinuria (PNH) screening: Flow cytometry for CD55/CD59 deficiency 1, 3
Glucose-6-phosphate dehydrogenase (G6PD) level: When oxidative stress or drug-induced hemolysis suspected 1, 3
Protein electrophoresis and cryoglobulin analysis: For paraprotein-associated hemolysis 1
Important Caveats and Pitfalls
Reticulocytopenia despite hemolysis occurs in 20-40% of autoimmune hemolytic anemia cases and represents a poor prognostic factor, indicating concurrent bone marrow suppression, nutritional deficiency, or autoimmune reaction against erythroid precursors 3, 5. In these cases, consider checking B12, folate, iron studies, copper, and parvovirus 1.
Elevated LDH and bilirubin are not specific for hemolysis and can occur with liver disease, myocardial infarction, or tissue breakdown 5, 6. The combination of elevated LDH, decreased haptoglobin, elevated unconjugated bilirubin, and reticulocytosis together provides much higher specificity 4, 5.
Thrombocytopenia accompanying hemolysis suggests thrombotic microangiopathy (TTP, HUS) or Evans syndrome, requiring urgent hematology consultation and consideration of plasma exchange 2, 3.
Macrocytosis on CBC may reflect the elevated reticulocyte count (young red cells are larger) rather than a separate pathology 4.
Severity Assessment
The hemoglobin level defines clinical severity, not the degree of laboratory marker abnormality 5. Management decisions are based on hemoglobin thresholds (Grade 1: mild anemia; Grade 2: Hb 8-10 g/dL; Grade 3: Hb <8 g/dL; Grade 4: life-threatening) combined with symptomatology 1, 2, 3.