What lab tests are used to evaluate anemia?

Laboratory Tests for Anemia Evaluation

The minimum laboratory evaluation for anemia should include a complete blood count (CBC) with red cell indices, reticulocyte count, serum ferritin, transferrin saturation, and C-reactive protein (CRP). 1, 2

Initial Diagnostic Workup

Core Laboratory Tests

• Complete Blood Count (CBC):

  • Hemoglobin (preferred over hematocrit)
  • Red blood cell count
  • Mean corpuscular volume (MCV)
  • Mean corpuscular hemoglobin (MCH)
  • Mean corpuscular hemoglobin concentration (MCHC)
  • Red cell distribution width (RDW)
  • White blood cell count and differential
  • Platelet count 1, 2

• Reticulocyte Count: Evaluates bone marrow response to anemia 1

• Iron Studies:

  • Serum ferritin (marker for tissue iron stores)
  • Transferrin saturation (TSAT) (marker for iron available for erythropoiesis) 1, 2

• Inflammatory Markers:

  • C-reactive protein (CRP) 1, 2

Classification-Based Testing

The initial CBC results help classify anemia into three main categories, which guides further testing:

1. Microcytic Anemia (MCV <80 fL)

Additional tests:

• Serum iron
• Total iron-binding capacity (TIBC)
• Hemoglobin electrophoresis (to rule out thalassemia) 2, 3

2. Normocytic Anemia (MCV 80-100 fL)

Additional tests:

• Kidney function tests (creatinine, urea)
• Liver function tests
• Thyroid function tests
• Vitamin B12 and folate levels (if borderline high MCV)
• Haptoglobin, LDH, and bilirubin (if hemolysis suspected) 1, 2

3. Macrocytic Anemia (MCV >100 fL)

Additional tests:

• Vitamin B12 level
• Folate level
• Thyroid function tests
• Liver function tests 2, 3

Advanced Testing

For cases where initial testing is inconclusive:

• Peripheral blood smear examination
• Soluble transferrin receptor (sTfR)
• Percentage of hypochromic red cells
• Reticulocyte hemoglobin content (CHr)
• Lactate dehydrogenase (LDH)
• Haptoglobin (for hemolysis)
• Bone marrow examination 1, 2

Special Considerations

• Iron Deficiency: In non-dialysis CKD patients, ferritin levels <25 ng/ml in males and <11 ng/ml in females indicate insufficient iron stores 1

• Inflammatory Conditions: In patients with inflammatory conditions, transferrin saturation may be more reliable than ferritin, as ferritin acts as an acute-phase reactant 1, 2

• Pregnancy: Hemoglobin <11.0 g/dL in first trimester and <10.5 g/dL in second/third trimester indicates anemia 4

• Resource-Limited Settings: When ferritin testing is unavailable, CBC parameters can help identify iron deficiency anemia, with hematocrit <35.5%, MCV <84.10 fL, and MCH <29.15 pg showing good discriminatory power 5

Monitoring Frequency

• For patients with chronic kidney disease (CKD), screen for anemia at least yearly
• More frequent monitoring for patients with diabetes and CKD
• For patients on treatment for anemia, monitor hemoglobin levels regularly to assess response 1

Remember that hemoglobin is preferred over hematocrit for diagnosing anemia due to better reproducibility across laboratories and less susceptibility to storage time and patient variables like serum glucose 1.

When the cause of anemia remains unclear after extensive workup, consultation with a hematologist is appropriate 1.