What laboratory tests are recommended for diagnosing anemia?

Laboratory Tests for Diagnosing Anemia

The essential laboratory tests for diagnosing anemia include hemoglobin (preferred over hematocrit), complete blood count with indices, reticulocyte count, serum ferritin, and transferrin saturation. 1

Initial Diagnostic Tests

• Hemoglobin: Primary test for diagnosing anemia

  • Preferred over hematocrit due to better reproducibility across laboratories
  • Less affected by storage time and patient variables like serum glucose 2

• Complete Blood Count (CBC):

  • Includes white blood cells, red blood cells, hemoglobin, platelets
  • Red cell indices: MCV, MCH, MCHC, RDW
  • Abnormalities in two or more cell lines warrant hematology consultation 2
  • RDW >14.0% with low MCHC strongly suggests iron deficiency anemia 1

• Reticulocyte Count:

  • Evaluates bone marrow response to anemia
  • Can be expressed as absolute count or reticulocyte index (adjusted for degree of anemia)
  • Low count suggests iron deficiency, defective red cell production, or insufficient erythropoietin 2

Iron Status Assessment

• Serum Ferritin:

  • Surrogate marker for tissue iron stores
  • Ferritin <30 μg/L indicates iron deficiency in patients without inflammation
  • In patients with inflammation, values up to 100 μg/L may still indicate iron deficiency 1
  • In males, <25 ng/ml and in females <11 ng/ml predict insufficient iron stores 2
  • Caution: Acts as acute-phase reactant; may be elevated despite iron deficiency

• Transferrin Saturation (TSAT):

  • Represents iron available for erythropoiesis
  • More reliable than ferritin in chronic inflammation
  • Iron deficiency defined as TSAT <20% with ferritin 100-299 μg/L 1

Additional Tests Based on Clinical Suspicion

• Inflammatory Markers:

  • ESR and CRP help identify anemia of chronic disease
  • Normal values don't exclude iron deficiency 1

• Hemolysis Evaluation:

  • Haptoglobin, LDH, and bilirubin to rule out hemolytic causes 1

• Nutritional Deficiency Tests:

  • Vitamin B12 and folate levels when macrocytic anemia is present 1

Diagnostic Algorithm

1. Start with hemoglobin and CBC with indices

   • If hemoglobin is low, classify based on MCV:
     • Microcytic (low MCV): Proceed to iron studies
     • Normocytic: Check reticulocyte count
     • Macrocytic: Consider B12/folate testing

2. Evaluate iron status

   • Ferritin and transferrin saturation
   • Consider inflammatory markers if ferritin is borderline

3. Assess bone marrow response

   • Reticulocyte count/index
   • Low count with adequate iron suggests other causes

Common Pitfalls to Avoid

• Relying solely on hemoglobin/hematocrit without investigating underlying cause 1
• Misinterpreting ferritin in the presence of inflammation 1
• Using serum iron alone (unreliable due to diurnal variations) 1
• Overlooking functional iron deficiency despite normal ferritin 1
• Accepting a positive dietary history as the sole cause of iron deficiency anemia without further investigation 1
• Failing to evaluate for other nutrient deficiencies in persistent anemia 1

By following this systematic approach to laboratory testing for anemia, clinicians can effectively diagnose the underlying cause and implement appropriate treatment strategies to improve patient outcomes.