Hemolytic Anemia Workup
A comprehensive hemolytic anemia workup should include complete blood count, markers of hemolysis, direct antiglobulin test, peripheral blood smear, and targeted testing to determine the specific cause of hemolysis. 1, 2
Initial Laboratory Evaluation
- Complete blood count (CBC) with red cell indices to confirm anemia and determine if it is normocytic, microcytic, or macrocytic 2
- Reticulocyte count - typically elevated in hemolytic anemia, indicating increased red cell production in response to hemolysis 1, 2
- Markers of hemolysis:
- Lactate dehydrogenase (LDH) - elevated in hemolysis 1, 3
- Unconjugated (indirect) bilirubin - elevated due to increased red cell breakdown 1, 3
- Haptoglobin - decreased or absent as it binds to free hemoglobin 1, 2
- Free hemoglobin in plasma or urine (hemoglobinuria) - may be present in intravascular hemolysis 3
Peripheral Blood Smear
- Essential for evaluating red cell morphology which can provide clues to the etiology 1
- Look for:
Immune vs. Non-immune Hemolysis Testing
- Direct antiglobulin test (DAT/Coombs test) - distinguishes immune from non-immune causes 1, 5
- Positive in immune-mediated hemolytic anemia
- Should include testing for both IgG and complement (C3d) 6
- If DAT positive, perform antibody elution studies to determine antibody specificity 5
- Indirect antiglobulin test to detect circulating antibodies 6
Testing for Specific Etiologies
For suspected autoimmune hemolytic anemia:
- Cold agglutinin titers if cold-reactive antibodies are suspected 6
- Paroxysmal nocturnal hemoglobinuria (PNH) screening by flow cytometry 1
- Evaluation for underlying conditions (lymphoproliferative disorders, autoimmune diseases) 6
For suspected hereditary hemolytic anemia:
- Red cell enzyme assays (particularly for pyruvate kinase and G6PD deficiency) 1
- Hemoglobin electrophoresis or high-performance liquid chromatography (HPLC) for hemoglobinopathies 3
- Osmotic fragility test or eosin-5-maleimide (EMA) binding test for membrane disorders 7
- Molecular/genetic testing for specific mutations when indicated 1
For suspected extrinsic causes:
- Coagulation studies (PT, PTT, fibrinogen, D-dimer) for microangiopathic hemolytic anemia 4
- ADAMTS13 activity for thrombotic thrombocytopenic purpura 4
- Evaluation for infections that can cause hemolysis 3
- Review of medications that may cause drug-induced hemolytic anemia 3
Additional Testing Based on Clinical Context
- Iron studies (serum ferritin, transferrin saturation) - may be elevated in chronic hemolysis 1, 2
- Vitamin B12 and folate levels - to rule out other causes of macrocytic anemia 2, 8
- Liver function tests - to assess for liver disease 8
- Kidney function tests - to evaluate for hemolytic uremic syndrome or complications of hemolysis 2
- Bone marrow examination - when there is suspicion of infiltrative disease or ineffective erythropoiesis 1, 8
Common Pitfalls to Avoid
- Failure to obtain reticulocyte count, which is crucial to differentiate hemolytic from other causes of anemia 2, 3
- Interpreting isolated laboratory abnormalities without clinical context 3, 4
- Overlooking drug-induced hemolytic anemia, which requires thorough medication history 3
- Delaying diagnosis in severe cases, which can lead to life-threatening complications 4
- Transfusing before completing diagnostic workup, which can interfere with test results 1, 4
Special Considerations
- Recent blood transfusion can affect test results, particularly DAT and enzyme assays 1
- Family history should be obtained to identify potential hereditary causes 1
- In neonates with jaundice, hemolytic workup should be prioritized to prevent kernicterus 3
- In transfusion-dependent patients with undiagnosed anemia, consider rare enzymopathies like pyruvate kinase deficiency 1