Treatment of Low Ferritin (Iron Deficiency)
Oral iron supplementation with ferrous sulfate 325 mg daily (or on alternate days to reduce side effects) is the first-line treatment for iron deficiency, with intravenous iron reserved for specific situations including malabsorption, intolerance, ongoing blood loss, chronic inflammatory conditions, or pregnancy. 1
Diagnostic Thresholds for Treatment
The ferritin cutoff that triggers treatment depends on clinical context:
- Healthy adults without inflammation: Ferritin <30 μg/L indicates iron deficiency requiring treatment 2, 3, 1
- With inflammation present: Ferritin <45 μg/L warrants consideration for treatment, as ferritin is an acute phase reactant that can be falsely elevated 4, 2
- Optimal target for treatment: Continue therapy until ferritin >50 μg/L, which represents the body's physiologic threshold 2, 5
The British Society of Gastroenterology notes that ferritin <15 μg/L has 99% specificity for iron deficiency, while ferritin <45 μg/L provides 92% specificity and is more appropriate when inflammation may be present 4.
First-Line Treatment: Oral Iron
Dosing: Ferrous sulfate 325 mg daily (containing 65 mg elemental iron) is standard 6, 1. Alternate-day dosing may improve tolerability with similar efficacy 1.
Practical considerations:
- Use preparations with 28-50 mg elemental iron to minimize gastrointestinal side effects while maintaining efficacy 3
- Take with vitamin C to enhance absorption 2
- Avoid tea, coffee, calcium supplements, and antacids around dosing time as these inhibit absorption 2
When to Use Intravenous Iron
IV iron is indicated as first-line therapy in specific populations 1:
- Malabsorption disorders: Celiac disease, post-bariatric surgery, inflammatory bowel disease
- Oral iron intolerance: Significant gastrointestinal side effects preventing compliance
- Ongoing blood loss: When losses exceed oral replacement capacity
- Chronic inflammatory conditions: Chronic kidney disease, heart failure, inflammatory bowel disease, cancer 4, 1
- Pregnancy: Second and third trimesters 1
In chronic kidney disease patients on erythropoiesis-stimulating agents, IV iron is superior to oral iron and should be considered when ferritin is <800 ng/mL and transferrin saturation is <20% (functional iron deficiency) 4.
Monitoring and Duration of Treatment
Initial response check: Measure hemoglobin and ferritin after 4-8 weeks 2, 3
- Expect hemoglobin increase of 1-2 g/dL if treatment is effective 7
- If no response, consider malabsorption, ongoing blood loss, or incorrect diagnosis 7
Duration: Continue treatment for at least 3 months after hemoglobin normalizes to replenish iron stores 2
Long-term follow-up: Monitor ferritin every 6-12 months in high-risk populations (menstruating women, athletes, vegetarians, inflammatory bowel disease) 2, 3
Critical Pitfall to Avoid
Do not dismiss ferritin levels of 30-100 μg/L in symptomatic patients, especially those with chronic inflammatory conditions. The traditional "normal" ferritin ranges in many laboratories will miss 30-50% of women with depleted iron stores 5. In the presence of inflammation (elevated CRP), ferritin up to 100 μg/L may still represent true iron deficiency 4, 2.
Special Population: Non-Anemic Iron Deficiency
Patients with ferritin <30-35 μg/L but normal hemoglobin still warrant treatment if symptomatic (fatigue, exercise intolerance, restless legs, cognitive impairment) 2, 3, 1. This is particularly common in female athletes (15-35% prevalence) and menstruating women 2.
When NOT to Give Iron
Avoid iron supplementation when ferritin is normal or elevated without evidence of functional iron deficiency, as this is inefficient, causes side effects, and may be harmful 3. Long-term daily supplementation with normal ferritin values is not recommended 3.