What labs are used to diagnose anemia?

Diagnostic Laboratory Tests for Anemia

The essential laboratory tests for diagnosing anemia include a complete blood count (CBC) with hemoglobin measurement, reticulocyte count, iron studies (serum ferritin and transferrin saturation), and assessment of red cell morphology. 1

Initial Diagnostic Approach

Primary Laboratory Tests

• Hemoglobin measurement: Preferred over hematocrit due to better reproducibility across laboratories and less susceptibility to storage time or patient variables like serum glucose 1
• Complete Blood Count (CBC) including:
  • White blood cell count
  • Hemoglobin level
  • Platelet count
  • Red cell indices (MCV, MCH, MCHC)
  • Red blood cell distribution width (RDW)
• Reticulocyte count: Evaluates bone marrow response to anemia; can be reported as absolute count or reticulocyte index (adjusted for degree of anemia) 1

Iron Status Assessment

• Serum ferritin: Surrogate marker for tissue iron stores
• Transferrin saturation: Represents iron available for erythropoiesis
• Mean corpuscular volume (MCV): Late marker of iron deficiency 1

Diagnostic Algorithm Based on MCV Classification

Microcytic Anemia (MCV < 80 fL)

• Iron studies:
  • Serum ferritin (<30 μg/L indicates iron deficiency)
  • Transferrin saturation (low in iron deficiency)
  • RDW (elevated in iron deficiency)
• Hemoglobin electrophoresis: If thalassemia is suspected 2

Normocytic Anemia (MCV 80-100 fL)

• Reticulocyte count:
  • If elevated: Consider hemolysis or blood loss
  • If normal/decreased: Consider anemia of chronic disease, renal disease, or early iron deficiency 1, 3
• Additional tests if hemolysis suspected:
  • Serum haptoglobin (decreased)
  • Lactate dehydrogenase (elevated)
  • Bilirubin (elevated) 2

Macrocytic Anemia (MCV > 100 fL)

• Vitamin B12 and folate levels
• Liver function tests
• Thyroid function tests
• Reticulocyte count 4

Advanced or Specialized Testing

• Soluble transferrin receptor (sTfR): Helps differentiate between anemia of chronic disease and iron deficiency 2
• Inflammatory markers (CRP, ESR): To assess for underlying inflammation that may affect iron parameters 2
• Percent hypochromic red blood cells (PHRBC) and content of hemoglobin in red blood cells (CHr): May have better sensitivity/specificity than ferritin and transferrin saturation for functional iron deficiency, but less widely available 1

Important Clinical Considerations

• Abnormalities in two or more cell lines (white blood cells, red blood cells, platelets) warrant hematology consultation 1
• In patients with chronic kidney disease, ferritin interpretation is complicated by its role as an acute-phase reactant 1
• Ferritin may appear normal in iron deficiency with concurrent inflammation; values <100 μg/L should be considered suspicious in inflammatory states 2
• CBC parameters alone without iron studies may miss early iron depletion 5

Diagnostic Cut-off Values

• Iron deficiency: Ferritin <30 μg/L (more stringent values: <25 ng/ml in males, <11 ng/ml in females) 1, 6
• Iron deficiency anemia: Ferritin <30 μg/L with hemoglobin <120 g/L in women 6
• CBC parameters for iron deficiency anemia 6:
  • RBC count: <4.04 × 10¹²/L
  • MCV: <84.10 fL
  • MCHC: <337.5 g/L
  • MCH: <29.15 pg
  • Hematocrit: <35.5%

Remember that a single laboratory value should not be used in isolation to diagnose anemia, and the pattern of abnormalities across multiple parameters provides the most accurate diagnosis.