Blood Work Markers Indicating Hemolytic Anemia
The essential laboratory markers that confirm hemolytic anemia are elevated reticulocyte count, elevated lactate dehydrogenase (LDH), decreased or absent haptoglobin, and elevated indirect (unconjugated) bilirubin, combined with a peripheral blood smear to identify red blood cell morphology abnormalities. 1
Core Hemolytic Markers
The following laboratory findings establish the presence of hemolysis:
- Elevated reticulocyte count: Indicates compensatory bone marrow response to red cell destruction 1, 2
- Elevated LDH: Marker of intravascular hemolysis, though it can be normal in 25% of autoimmune hemolytic anemia cases 3, 4
- Decreased or absent haptoglobin: Reduced levels confirm hemolysis, as haptoglobin binds free hemoglobin 5, 1, 2
- Elevated indirect (unconjugated) bilirubin: Results from breakdown of hemoglobin 5, 1, 2, 4
Critical Diagnostic Tests
Beyond the core markers, these tests are mandatory for complete evaluation:
- Peripheral blood smear: Essential to identify schistocytes (indicating microangiopathic hemolysis), spherocytes (suggesting hereditary spherocytosis or autoimmune hemolytic anemia), or other morphologic abnormalities 1, 2
- Complete blood count: Defines severity through hemoglobin level and identifies thrombocytopenia, which suggests thrombotic microangiopathy or Evans' syndrome 5, 2
- Direct antiglobulin test (DAT/Coombs test): Must be performed before initiating treatment to differentiate immune from non-immune hemolysis 1, 6, 4
Additional Laboratory Parameters
When hemolysis is confirmed, obtain these markers for comprehensive assessment:
- Hemosiderinuria: Typical of chronic intravascular hemolysis, particularly in paroxysmal nocturnal hemoglobinuria 2
- Hyperferritinemia: Associated with chronic hemolysis 2
- Platelet count: Thrombocytopenia (<150,000/mm³ or 25% reduction) suggests thrombotic microangiopathy rather than isolated hemolytic anemia 5, 2
Important Clinical Caveats
Reticulocytopenia occurs in 20-40% of autoimmune hemolytic anemia cases and represents a poor prognostic factor, typically due to bone marrow involvement, nutritional deficiencies (iron/vitamins), infections, or autoimmune reaction against bone marrow precursors 2, 6. In these cases, the absence of elevated reticulocytes does not exclude hemolysis.
LDH can be normal in up to 25% of confirmed autoimmune hemolytic anemia cases, so normal LDH should not exclude the diagnosis when other markers are present 3. Conversely, elevated LDH, bilirubin, and reticulocytes can occur in conditions other than hemolysis (liver disease, kidney disease, malignancy), requiring careful clinical correlation 2, 6.
Schistocytes may be absent in early thrombotic microangiopathy due to low test sensitivity, so their absence should not exclude the diagnosis when clinical suspicion is high 5, 1.
Diagnostic Algorithm Based on DAT Result
Once hemolysis is confirmed with the above markers:
- If DAT positive: Evaluate for autoimmune hemolytic anemia (primary or secondary to lymphoproliferative disorders, autoimmune diseases, infections, or drugs) 1, 6, 4
- If DAT negative: Consider hereditary causes (membranopathies like hereditary spherocytosis, enzymopathies like pyruvate kinase or G6PD deficiency), paroxysmal nocturnal hemoglobinuria, or DAT-negative autoimmune hemolytic anemia 1, 6
Clinical History Requirements
Always obtain the following information alongside laboratory testing:
- Timing of last blood transfusion: Recent transfusions affect enzyme assay interpretation and reticulocyte counts 5, 1
- Neonatal jaundice history: Suggests hereditary hemolytic conditions 5, 1
- Drug exposures: Essential for identifying drug-induced hemolysis or oxidant-triggered G6PD deficiency 1, 6
- Family history: Indicates possible hereditary conditions requiring genetic testing 5, 1