When should ferritin levels be checked in patients taking iron supplements, such as ferrous sulfate (iron), for iron deficiency anemia?

When to Check Ferritin with Iron Supplements

For patients on oral iron supplementation, recheck ferritin and complete iron studies at 3 months to assess iron store replenishment; however, check hemoglobin earlier at 4 weeks to confirm treatment response. 1, 2, 3

Initial Response Assessment (4 Weeks)

• Check hemoglobin at 4 weeks after starting oral iron to determine if therapy is working 1, 3
• Expect hemoglobin to rise by 1-2 g/dL within 4-8 weeks of starting treatment 1, 2
• If hemoglobin has not increased by at least 1 g/dL at 4 weeks, consider switching to intravenous iron 1

Comprehensive Iron Store Assessment (3 Months)

• Recheck complete iron panel (hemoglobin, ferritin, and transferrin saturation) at 3 months to assess whether iron stores have been adequately replenished 1, 2, 3
• Continue oral iron for a full 3 months after hemoglobin normalizes to ensure adequate bone marrow iron store repletion 1, 3
• Stopping iron prematurely (when hemoglobin normalizes but before stores are replete) results in recurrence of iron deficiency in >50% of patients within 1 year 2, 3

Different Timing for Intravenous Iron

Critical pitfall: Do not check ferritin within 4 weeks of IV iron administration, as ferritin becomes falsely elevated and unreliable during this period 2, 3

• For large IV iron doses (≥1000 mg), wait 4-8 weeks before rechecking iron parameters for accurate assessment 2, 3
• For smaller IV iron doses (100-500 mg), wait at least 1-2 weeks before checking ferritin 2, 3
• Hemoglobin can still be checked at 4 weeks after IV iron to assess clinical response 2, 3

Long-Term Monitoring After Correction

• After achieving normal hemoglobin and iron stores, monitor hemoglobin and red cell indices every 3 months for the first year, then annually 2, 3
• If hemoglobin or mean corpuscular volume (MCV) falls below normal during follow-up, resume iron supplementation 2, 3

Special Population: Chronic Kidney Disease Patients on ESAs

• For CKD patients receiving erythropoietin-stimulating agents (ESAs), monitor iron status (ferritin and transferrin saturation) every 1-3 months depending on clinical stability 1, 2, 3
• Test more frequently when initiating or increasing ESA dose, when there is blood loss, or when monitoring response after IV iron 1, 2, 3
• Target ferritin >100-200 ng/mL and transferrin saturation >20% in CKD patients 1, 2

Special Population: Inflammatory Bowel Disease

• Monitor for recurrent iron deficiency every 3 months for at least a year after correction, then between 6-12 months thereafter 2, 3
• Re-treat with IV iron when serum ferritin drops below 100 μg/L or hemoglobin falls below 12 g/dL (women) or 13 g/dL (men) 2, 3

Key Pitfalls to Avoid

• Checking ferritin too soon after IV iron (within 4 weeks) yields falsely elevated readings that do not reflect true iron stores 2, 3
• Stopping oral iron when hemoglobin normalizes without continuing for an additional 3 months results in inadequate iron store repletion and early recurrence 1, 3
• Not checking hemoglobin at 4 weeks means missing patients who are not responding to oral iron and need IV therapy 1, 3