At what ferritin level should iron supplements be started?

Iron Supplementation Thresholds Based on Ferritin Levels

Iron supplementation should be initiated when serum ferritin is ≤75 ng/mL or transferrin saturation is <20% in adults with clinically significant conditions like restless legs syndrome, while in children, supplementation should begin when ferritin is <50 ng/mL. 1

Ferritin Thresholds for Iron Supplementation by Population

Adults

• General threshold: Ferritin ≤75 ng/mL OR transferrin saturation <20% 1
• Special case: For ferritin between 75-100 ng/mL, IV iron only (not oral) is recommended 1
• Absolute iron deficiency: Ferritin <30 ng/mL 1, 2, 3
• With inflammatory conditions: Consider iron deficiency when ferritin <100 ng/mL 1

Children

• General threshold: Ferritin <50 ng/mL 1, 4
• Age-specific thresholds:
  • Ages 6-12 years: Ferritin <15 μg/L 4
  • Ages 12-15 years: Ferritin <20 μg/L 4

Diagnostic Considerations

Iron Status Assessment

• Essential tests: Serum ferritin, transferrin saturation (calculated from iron and total iron binding capacity) 1, 3
• Timing: Morning testing is ideal, avoiding iron-containing supplements/foods for 24 hours prior 1
• Additional markers:
  • Hypochromic, microcytic red cells
  • Low cellular Hb content in reticulocytes (CHr <28 pg)
  • Increased percentage of hypochromic RBCs (>5%) 1

Interpreting Results with Inflammation

• Ferritin is an acute phase reactant and may be falsely elevated with inflammation 1, 4
• Check C-reactive protein to exclude acute phase reaction 2
• In cancer and other inflammatory conditions, raise ferritin cutoff to 100 ng/mL 1

Treatment Approaches

Oral Iron Therapy

• First-line approach for most patients 3
• Dosing:
  • Adults: 28-50 mg elemental iron daily or on alternate days 2, 3
  • Children: 3 mg/kg/day for iron deficiency anemia 4
• Administration: Best absorbed when taken in the morning on an empty stomach 4
• Duration: Continue for 3 months after hemoglobin normalization to replenish iron stores 4

Intravenous Iron Therapy

• Indications:
  • Oral iron intolerance
  • Poor absorption (celiac disease, post-bariatric surgery)
  • Chronic inflammatory conditions (CKD, heart failure, IBD, cancer)
  • Ongoing blood loss
  • During second and third trimesters of pregnancy 3
  • When ferritin is between 75-100 ng/mL in RLS patients 1

Monitoring Response

• Check hemoglobin response within 4 weeks of starting therapy 4
• If no increase of 1-2 g/dL in hemoglobin after 4 weeks, consider malabsorption, continued bleeding, or other causes 5
• Target ferritin >100 μg/L to ensure adequate iron stores are replenished 4
• Regular monitoring every 6-12 months for patients with repeatedly low ferritin 2

Common Pitfalls to Avoid

1. Overreliance on ferritin alone in inflammatory conditions (may be falsely elevated) 4
2. Prescribing multiple daily doses of oral iron (may not improve absorption due to hepcidin elevation) 4
3. Using modified-release preparations of oral iron (less effective due to reduced absorption) 4
4. Stopping treatment too early before iron stores are replenished 4
5. Excessive blood transfusions instead of appropriate iron therapy 4
6. Long-term daily supplementation in the presence of normal or high ferritin (potentially harmful) 2

Iron deficiency is a common and treatable condition that significantly impacts quality of life. Research shows that even non-anemic iron deficiency (ferritin ≤15 ng/mL) can cause significant fatigue that improves with iron supplementation 6, 7. Early identification and appropriate treatment based on established ferritin thresholds can effectively address this widespread nutritional deficiency.