What is the diagnostic workup for anemia?

Diagnostic Workup for Anemia

The diagnostic workup for anemia should begin with a complete blood count (CBC) with reticulocyte index, followed by targeted testing based on the classification of anemia as microcytic, normocytic, or macrocytic, and whether it is regenerative or non-regenerative. 1

Initial Evaluation

First-Line Tests

• Complete blood count (CBC) 1
• Reticulocyte count/index 1
• Peripheral blood smear examination 1
• Markers of hemolysis (LDH, unconjugated bilirubin, haptoglobin) 2, 1

Classification Based on Initial Testing

1. Classify by MCV (Mean Corpuscular Volume):

   • Microcytic (MCV <80 fL)
   • Normocytic (MCV 80-100 fL)
   • Macrocytic (MCV >100 fL) 1

2. Classify by Reticulocyte Index:

   • Regenerative anemia: Reticulocyte index >2.0 (suggests bleeding or hemolysis)
   • Non-regenerative anemia: Reticulocyte index <2.0 (suggests bone marrow production problem) 1

Further Workup Based on Classification

Microcytic Anemia Workup

• Serum ferritin (primary marker for tissue iron stores)
  • <15 μg/L: Highly specific for iron deficiency (specificity 0.99)
  • <30 μg/L: Indicates absent/low iron stores in non-inflammatory states
  • <45 μg/L: Optimal cutoff for clinical practice 1
• Transferrin saturation (<20% suggests iron deficiency) 1
• Serum iron and total iron-binding capacity (TIBC) 3
• Hemoglobin electrophoresis (to rule out thalassemias) 3
• Erythrocyte size-distribution width (RDW) - helpful in distinguishing iron deficiency from thalassemia minor 3

Normocytic Anemia Workup

• If regenerative (reticulocyte index >2.0):

  • Direct Coombs test (for autoimmune hemolytic anemia) 3
  • Hemolysis panel (haptoglobin, LDH, bilirubin) 2, 1
  • Peripheral smear for morphological abnormalities (spherocytes, schistocytes) 1

• If non-regenerative (reticulocyte index <2.0):

  • Renal function tests (creatinine, BUN) 1
  • Inflammatory markers (CRP, ESR) 4
  • Thyroid function tests
  • Vitamin B12 and folate levels 4
  • Consider bone marrow examination if other tests inconclusive

Macrocytic Anemia Workup

• Vitamin B12 and folate levels 4, 3
• Liver function tests
• Thyroid function tests
• Reticulocyte count
• Consider bone marrow examination if megaloblastic features present 3

Special Considerations

For Suspected Hemolytic Anemia

• Complete hemolysis panel (haptoglobin, LDH, indirect bilirubin) 2
• Direct and indirect Coombs test 3
• Peripheral blood smear for RBC morphology 2
• Enzyme assays (e.g., G6PD, pyruvate kinase) when indicated 2

For Suspected Anemia of Chronic Disease

• Ferritin (often elevated due to inflammation)
• Transferrin saturation (typically low)
• Inflammatory markers (CRP, ESR)
• Hepcidin levels (if available) 4
• Evaluation of underlying chronic conditions 4

Common Pitfalls and Caveats

• Ferritin interpretation: Ferritin is an acute phase reactant and may be falsely elevated in inflammatory states. In patients with inflammation, higher cutoff values (up to 100 μg/L) may be needed to diagnose iron deficiency 1

• Recent transfusion: Blood transfusions can mask the true nature of anemia. Always document time of last transfusion when interpreting results 2

• Mixed anemias: Multiple causes of anemia can coexist (e.g., iron deficiency with B12 deficiency). Consider comprehensive testing in cases that don't fit a single pattern 4

• Timing of testing: Hemolysis markers may be affected by sample handling and timing. Proper collection and processing are essential 2

• Reticulocyte response interpretation: A normal or low reticulocyte count in the setting of anemia indicates an inadequate bone marrow response and requires further investigation 1