How do you diagnose and manage iron deficient anemia based on lab results?

Interpreting Labs for Iron Deficiency Anemia

Serum ferritin is the most powerful test for diagnosing iron deficiency anemia, with additional tests like transferrin saturation, hemoglobin, and red cell indices providing a complete diagnostic picture. 1

Diagnostic Approach

Initial Laboratory Assessment

• Complete blood count (CBC) with red cell indices is the first step in evaluating for iron deficiency anemia 1
• Hemoglobin and hematocrit are commonly used screening tests due to low cost and ease of performance, but they are late indicators of iron deficiency 1
• Red cell indices (MCV, MCH, MCHC) provide sensitive indication of iron deficiency in the absence of chronic disease or hemoglobinopathy 1, 2
• Elevated red cell distribution width (RDW >14.0%) with microcytosis strongly suggests iron deficiency anemia 2

Confirmatory Tests

• Serum ferritin is the most sensitive and specific test for iron deficiency 1
  • <30 μg/L confirms iron deficiency in the absence of inflammation 2
  • <100 μg/L suggests iron deficiency in the presence of inflammation 1
• Transferrin saturation <20% indicates inadequate iron supply for erythropoiesis 1
• In the presence of inflammation with ferritin between 30-100 μg/L and transferrin saturation <20%, a combination of true iron deficiency and anemia of chronic disease is likely 1

Diagnostic Patterns

• Microcytic anemia (low MCV) with high RDW: strongly suggests iron deficiency anemia 2
• Microcytic anemia with normal RDW: consider thalassemia minor 2
• Normocytic anemia with high RDW: may indicate early iron deficiency, vitamin B12/folate deficiency, or hemolysis 2
• Normal MCV with high RDW: may indicate combined iron deficiency with macrocytosis (e.g., from B12/folate deficiency) 2

Management Approach

Treatment Indications

• Iron supplementation is recommended for all patients with iron deficiency anemia 1
• The goal is to normalize both hemoglobin levels and iron stores 1
• An increase in hemoglobin of at least 2g/dL within 4 weeks of treatment indicates adequate response 1

Route of Administration

• Oral iron should be the initial treatment for most patients 1
• Intravenous iron should be considered as first-line treatment in patients with: 1
  • Inflammatory bowel disease
  • Intolerance to oral iron
  • Poor absorption
  • Ongoing blood loss
  • Need for rapid hemoglobin improvement

Monitoring Response

• Hemoglobin should increase by at least 2g/dL within 4 weeks of adequate iron therapy 1
• Transferrin saturation and serum ferritin should normalize with successful treatment 3, 4
• If hemoglobin fails to rise appropriately, consider:
  • Ongoing blood loss
  • Non-adherence to oral therapy
  • Malabsorption
  • Incorrect diagnosis 1

Special Considerations

Inflammatory Conditions

• In inflammatory states, ferritin may be falsely elevated as an acute phase reactant 1, 2
• Use higher ferritin threshold (<100 μg/L) to diagnose iron deficiency when inflammation is present 1
• Consider measuring C-reactive protein (CRP) to assess for inflammation 2

Population-Specific Evaluation

• All premenopausal women with iron deficiency anemia should be screened for celiac disease 1
• All men and postmenopausal women with iron deficiency anemia should undergo gastrointestinal evaluation (upper and lower endoscopy) unless there is a clear non-GI source of blood loss 1
• Pregnant women may require higher doses of iron supplementation due to increased demands 1

Common Pitfalls

• Relying solely on hemoglobin/hematocrit for diagnosis misses early iron deficiency 1
• Failing to consider inflammation when interpreting ferritin levels 1, 2
• Not investigating the underlying cause of iron deficiency, especially in men and postmenopausal women 1
• Using fecal occult blood testing for investigation of iron deficiency anemia is not beneficial 1