How soon after starting oral iron therapy should ferritin levels be rechecked?

Timing for Rechecking Ferritin After Starting Oral Iron

Recheck hemoglobin at 4 weeks and complete iron studies (including ferritin) at 3 months after starting oral iron therapy. 1

Initial Hemoglobin Assessment at 4 Weeks

• Check hemoglobin level at 4 weeks to determine if treatment is working 1, 2
• You should expect a hemoglobin rise of 1-2 g/dL within 4-8 weeks of starting oral iron 1
• This early check identifies non-responders who need alternative therapy (such as switching to IV iron) 2

Comprehensive Iron Studies at 3 Months

• Recheck complete iron studies at 3 months, including hemoglobin, ferritin, and transferrin saturation 1, 3
• This 3-month timepoint assesses whether iron stores are being adequately replenished, not just whether hemoglobin is improving 1
• Continue oral iron for a full 3 months after hemoglobin normalizes to ensure adequate marrow iron store repletion 1

Critical Pitfall to Avoid

• Stopping iron when hemoglobin normalizes without continuing for an additional 3 months results in recurrence of iron deficiency in >50% of patients within 1 year 1
• The goal is not just to correct anemia but to replenish iron stores, which takes longer than hemoglobin correction 1

Different Timing for IV Iron (If Switched)

If oral iron fails and you switch to IV iron:

• Do not check ferritin within 4 weeks of IV iron administration because ferritin becomes falsely elevated and unreliable during this period 1, 3
• For IV iron doses ≥1000 mg, wait 4-8 weeks before rechecking iron parameters 1, 3
• For smaller IV iron doses (100-500 mg), wait at least 1-2 weeks before checking iron studies 1
• Hemoglobin can still be checked at 4 weeks after IV iron to assess response 1

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 1, 3
• If hemoglobin or MCV falls below normal during follow-up, resume iron supplementation 1

Special Population: Chronic Kidney Disease

For CKD patients on erythropoietin-stimulating agents (ESA):

• Monitor iron status (ferritin and transferrin saturation) at least every 3 months during ESA therapy 4, 1
• Test iron status more frequently when initiating or increasing ESA dose, when there is blood loss, or when monitoring response after IV iron 4
• Target ferritin >100-200 ng/mL and transferrin saturation >20% in CKD patients 1

Special Population: Inflammatory Bowel Disease

For IBD patients:

• Monitor for recurrent iron deficiency every 3 months for at least a year after correction, then between 6-12 months thereafter 4
• 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) 4

Factors That Impair Oral Iron Response

• Proton pump inhibitors significantly decrease oral iron absorption 5
• In patients on PPIs, only 16% had normal hemoglobin response (rise >2 g/dL) and only 40% had normal ferritin response (rise >20 μg/dL) at 3 months 5
• Consider high-dose oral iron for longer duration or switching to IV iron in patients taking PPIs 5