What are optimal iron levels?

Optimal Iron Levels

Optimal iron levels vary by clinical context, but for general populations, serum ferritin ≥30 ng/mL and transferrin saturation ≥20% indicate adequate iron stores, while specific disease states require higher targets.

General Population Thresholds

Iron Deficiency Diagnosis

• Serum ferritin <15 ng/mL is highly specific (99%) for absolute iron deficiency in healthy individuals without inflammation 1
• Ferritin <30 ng/mL generally indicates depleted iron stores in the absence of inflammatory conditions 1, 2
• Transferrin saturation <20% confirms iron-deficient erythropoiesis 1
• In the presence of inflammation, ferritin up to 45-50 ng/mL may still represent iron deficiency, as ferritin is an acute phase reactant that can be falsely elevated 1, 3

Normal Reference Values

• Average serum ferritin in healthy populations: 135 μg/L for men, 43 μg/L for women, and approximately 30 μg/L for children aged 6-24 months 1
• Each 1 μg/L of serum ferritin corresponds to approximately 10 mg of stored iron 1

Disease-Specific Optimal Targets

Chronic Kidney Disease (CKD)

For CKD patients with hemoglobin <110 g/L, maintain ferritin ≥100 ng/mL and transferrin saturation ≥20% 1

• Most hemodialysis patients achieve target hemoglobin with ferritin levels between 100-800 ng/mL and transferrin saturation >20% 1
• Withhold IV iron when ferritin >800 ng/mL and/or transferrin saturation >50% for up to 3 months, then reassess 1
• Upper safety limit: ferritin should not exceed 800 ng/mL in routine management 1

Inflammatory Bowel Disease (IBD)

Target ferritin levels of 100-400 μg/L to prevent recurrence of iron deficiency 1

• Post-treatment ferritin >400 μg/L prevents iron deficiency recurrence for 1-5 years better than lower levels 1
• Reinitiate IV iron when ferritin drops below 100 μg/L or hemoglobin falls below 12-13 g/dL (gender-dependent) 1
• Transferrin saturation 30-40% and ferritin 200-500 μg/L are optimal when using erythropoiesis-stimulating agents 1
• Upper safety threshold: transferrin saturation <50% and ferritin <800 μg/L should guide therapy limits 1

Cancer-Related Anemia

Absolute iron deficiency: transferrin saturation <20% and ferritin <30 ng/mL 1 Functional iron deficiency: transferrin saturation 20-50% and ferritin 30-800 ng/mL 1

• Iron therapy is appropriate when ferritin is between 30-800 ng/mL if transferrin saturation remains suboptimal 1
• Upper safety limits: transferrin saturation >50% or ferritin >800 ng/mL warrant caution and risk-benefit assessment 1

Clinical Interpretation Caveats

Inflammatory Conditions

• Ferritin >150 μg/L is unlikely to represent absolute iron deficiency, even with inflammation 1
• In chronic inflammatory states, use ferritin <45 μg/L as a more appropriate cutoff (specificity 92%) rather than <15 μg/L 1
• Consider soluble transferrin receptor/log ferritin ratio when ferritin is 50-100 μg/L in normocytic anemia, as standard ferritin cutoffs have poor negative predictive value (22%) at 50 μg/L 3

Pregnancy

• Iron deficiency affects up to 84% of pregnant women in the third trimester 2
• Normal ferritin measured in first or second trimester may not predict adequate iron status later in pregnancy 1

Treatment Targets by Route

Oral Iron Therapy

• Indicated for mild anemia in clinically inactive disease without prior oral iron intolerance 1
• Maximum recommended dose: 100 mg elemental iron per day in IBD patients to minimize gastrointestinal side effects 1
• Standard dosing for general iron deficiency: ferrous sulfate 325 mg daily (65 mg elemental iron) or alternate-day dosing 2

Intravenous Iron Therapy

• Preferred when ferritin <100 ng/mL with hemoglobin <100 g/L (severe anemia) 1
• Required for malabsorption states, ongoing blood loss, chronic inflammatory conditions, and second/third trimester pregnancy 2
• Maintenance targets post-correction: ferritin 100-800 ng/mL, transferrin saturation 20-50% 1

The key principle is that optimal iron levels must balance adequate stores for erythropoiesis (ferritin ≥30-100 ng/mL depending on condition) against risks of iron overload (ferritin >800 ng/mL, transferrin saturation >50%), with higher targets justified in chronic inflammatory states and CKD where functional iron deficiency predominates.