What laboratory tests are used to diagnose anemia?

Laboratory Tests for Diagnosing Anemia

The essential laboratory tests for diagnosing anemia include hemoglobin, complete blood count with red cell indices, reticulocyte count, serum ferritin, and transferrin saturation. 1

Core Laboratory Tests

Initial Assessment

• Hemoglobin: Primary diagnostic marker for anemia (preferred over hematocrit)

  • Women: <12.0 g/dL indicates anemia
  • Men: <13.0 g/dL indicates anemia 1
  • More reproducible across laboratories with lower coefficients of variation compared to hematocrit 2
  • Not affected by sample storage time or patient variables like serum glucose 2

• Complete Blood Count (CBC):

  • Red blood cell count
  • White blood cell count
  • Platelet count
  • Red cell indices:
    • Mean Corpuscular Volume (MCV): Classifies anemia as microcytic (<80 fL), normocytic (80-100 fL), or macrocytic (>100 fL) 1
    • Mean Corpuscular Hemoglobin (MCH)
    • Mean Corpuscular Hemoglobin Concentration (MCHC)
    • Red Cell Distribution Width (RDW): Important for differentiating causes of microcytic anemia 1, 3
      • Low MCV + Normal RDW → Thalassemia minor
      • Low MCV + Elevated RDW → Iron deficiency anemia

Iron Status Assessment

• Serum Ferritin: Surrogate marker for tissue iron stores 2

  • <15 μg/L indicates iron deficiency 1
  • Can be falsely elevated during inflammation (acute phase reactant) 2

• Transferrin Saturation (TSAT): Represents iron available for erythropoiesis 2

  • <20% indicates iron deficiency 1
  • Less affected by inflammation than ferritin 2

• Reticulocyte Count: Evaluates bone marrow response to anemia 2

  • 10×10⁹/L suggests regenerative anemia and warrants hemolysis workup 1

  • Can be expressed as absolute count or reticulocyte index (adjusted for degree of anemia) 2

Additional Tests Based on Initial Findings

For Suspected Iron Deficiency

• Total Iron Binding Capacity (TIBC)
• Percent Hypochromic Red Blood Cells (PHRBC): >10% indicates iron deficiency 1
• Reticulocyte Hemoglobin Content (RetHe): <29 pg indicates iron deficiency 1

For Suspected Nutritional Deficiencies

• Vitamin B12 levels: For macrocytic anemia 1
• Folate levels: For macrocytic anemia 1

For Suspected Chronic Disease or Inflammation

• C-reactive protein (CRP): To assess contribution of inflammation 2, 1

For Suspected Renal Disease

• Creatinine: To assess renal function 1

Interpretation Pitfalls

1. Normal hemoglobin/hematocrit does not rule out iron depletion

   • Iron depletion can exist with normal hemoglobin levels 4
   • CBC measures alone without iron status indicators may miss early iron deficiency 4

2. Ferritin interpretation challenges

   • Falsely elevated in inflammation, masking iron deficiency 2
   • In chronic kidney disease patients, ferritin levels in isolation can be misleading 2

3. Consequences of misdiagnosis

   • False-negative: Missing untreated anemia and its causes
   • False-positive: Unnecessary treatment or expensive testing 5

Special Considerations

• Pregnant women: Higher iron requirements (30-60 mg/day) 1
• Athletes: Higher prevalence of iron deficiency (15-35%, some studies >50%) 2
• Post-bariatric surgery patients: Require regular monitoring 1
• Patients with thalassemia: Should avoid excessive iron supplementation 1

By systematically applying these laboratory tests and understanding their interpretation in context, clinicians can accurately diagnose anemia and its underlying causes, leading to appropriate treatment and improved patient outcomes.