How is iron deficiency diagnosed and treated?

Diagnosis and Treatment of Iron Deficiency

Iron deficiency is diagnosed by measuring serum ferritin and transferrin saturation (TSAT), with diagnostic criteria depending on the presence of inflammation. In patients without inflammation, serum ferritin <30 μg/L indicates iron deficiency, while in patients with inflammation, serum ferritin up to 100 μg/L may still be consistent with iron deficiency 1, 2.

Diagnostic Approach

Laboratory Testing

• Initial screening: Complete blood count (CBC) including hemoglobin, MCV, RDW
• Confirmatory testing: Serum ferritin and transferrin saturation (TSAT)
• Additional testing when indicated: Reticulocyte count, CRP (to assess inflammation)

Diagnostic Criteria

1. Without inflammation:

   • Serum ferritin <30 μg/L 1
   • TSAT <16% 1

2. With inflammation (elevated CRP or clinical evidence of inflammation):

   • Serum ferritin <100 μg/L 1
   • TSAT <20% 1
   • If ferritin 30-100 μg/L and TSAT <20%, a combination of true iron deficiency and anemia of chronic disease is likely 1

3. Anemia of chronic disease:

   • Serum ferritin >100 μg/L
   • TSAT <20% 1

Important Considerations

• Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) are unreliable markers of iron deficiency status 1
• Red cell distribution width (RDW) >14% with low MCHC is highly suggestive of iron deficiency 2
• Serum iron alone should not be used as a marker of iron status due to large diurnal variations 1

Treatment Approach

Oral Iron Therapy

• First-line treatment: Ferrous sulfate 325 mg daily or on alternate days (providing 65 mg elemental iron) 2, 3
• Duration: Continue for 3 months after hemoglobin normalizes to replenish iron stores 2
• Expected response: 1-2 g/dL increase in hemoglobin within 2-4 weeks 2

Intravenous Iron Therapy

Indicated for patients with:

• Oral iron intolerance
• Poor absorption (celiac disease, post-bariatric surgery)
• Chronic inflammatory conditions (IBD, CKD, heart failure)
• Ongoing blood loss
• During second and third trimesters of pregnancy 3

Options include:

• Iron sucrose (Venofer): Administered as slow IV injection or infusion 4
• Ferric carboxymaltose: Appropriate for many patients with chronic conditions 1

Monitoring

• Check hemoglobin weekly until stable, then monthly
• Monitor iron parameters (ferritin, TSAT) regularly
• Re-evaluate iron status after 3 months of treatment 2

Special Considerations

Inflammatory Bowel Disease

• Iron deficiency is common (present in up to 90% of patients) 3
• Evaluation of iron status should be part of routine assessment 1
• IV iron may be preferred due to absorption issues and GI side effects of oral iron

Heart Failure

• Iron deficiency affects 37-61% of heart failure patients 3
• Defined as ferritin <100 μg/L or ferritin 100-299 μg/L with TSAT <20% 1
• IV ferric carboxymaltose has shown benefits in symptomatic heart failure patients 1

Common Pitfalls

• Misinterpreting ferritin levels in the presence of inflammation
• Relying solely on hemoglobin or MCV for diagnosis
• Inadequate duration of iron therapy
• Deferring iron replacement while awaiting investigations 2
• Accepting a positive dietary history as the sole cause of iron deficiency without GI investigation 2

Iron deficiency is a common condition that requires proper diagnosis and treatment to improve patient outcomes. The diagnostic approach should include both ferritin and transferrin saturation measurements, with interpretation based on the presence or absence of inflammation.