When should I follow up after starting oral ferrous sulfate (325 mg every other day with vitamin C) for early iron‑deficiency anemia?

Follow-Up Timing for Oral Iron Supplementation in Early Iron-Deficiency Anemia

Recheck CBC and iron studies at 4 weeks after starting ferrous sulfate to confirm adequate hemoglobin response, then continue treatment for a total of 3 months after hemoglobin normalizes to fully replenish iron stores. 1, 2

Initial Response Assessment (2–4 Weeks)

• Check hemoglobin at 2 weeks to predict treatment success: an increase of ≥10 g/L (≥1 g/dL) strongly predicts subsequent treatment success with 90% sensitivity and 79% specificity. 2, 3
• If hemoglobin fails to rise by at least 10 g/L at 2 weeks, this strongly predicts treatment failure and warrants investigation for non-compliance, continued blood loss, malabsorption, or concurrent vitamin B12/folate deficiency. 2
• The 4-week visit is the standard monitoring point recommended by multiple guidelines to assess hemoglobin response and verify that therapy is working. 4, 1, 2

Continuation and Completion of Therapy

• Continue oral iron for approximately 3 months after hemoglobin normalizes to ensure adequate repletion of bone marrow iron stores, not just correction of anemia. 4, 1, 2, 5
• This means total treatment duration is typically 3–6 months depending on how quickly hemoglobin normalizes. 4
• Monitor hemoglobin every 4 weeks until it normalizes, then continue treatment for the additional 3-month repletion phase. 2

Long-Term Surveillance

• Monitor blood counts every 6 months initially after completing therapy to detect recurrent iron deficiency, especially if the underlying cause (heavy menses, dietary deficiency) has not been fully addressed. 1, 2

Optimizing Your Current Regimen

Your plan to use ferrous sulfate 325 mg every other day with vitamin C is well-supported by recent evidence:

• Alternate-day dosing significantly increases fractional iron absorption compared to daily dosing because doses ≥60 mg elemental iron trigger hepcidin elevation lasting 24 hours, which blocks absorption of subsequent doses by 35–45%. 1, 2, 3
• Every-other-day dosing reduces gastrointestinal side effects while maintaining efficacy, though the rate of hemoglobin rise may be slightly slower initially compared to daily dosing. 1, 2, 3
• Taking iron in the morning on an empty stomach with 500 mg vitamin C maximizes absorption; avoid food, coffee, tea, or calcium-containing products for at least 1–2 hours. 1, 6

When to Escalate Care

• Consider switching to intravenous iron if hemoglobin fails to rise after 2–4 weeks of adherent oral therapy, if intolerable gastrointestinal side effects persist despite dosing adjustments, or if there is evidence of malabsorption (celiac disease, inflammatory bowel disease, prior gastric surgery). 1, 2
• Intravenous iron produces a clinically meaningful hemoglobin response within one week and can replenish total body iron stores in one or two infusions. 2, 5

Evaluation for Underlying Causes

• Investigate the source of iron loss if iron studies worsen or fail to improve despite adherent therapy: consider bidirectional endoscopy in postmenopausal women or men, screen for celiac disease with tissue transglutaminase antibodies, and evaluate menstrual history in premenopausal women. 1
• Heavy menstrual bleeding, occult gastrointestinal blood loss, and dietary insufficiency are the most common causes requiring concurrent management. 1

Common Pitfalls to Avoid

• Do not discontinue iron therapy prematurely when hemoglobin normalizes—continue for 3 additional months to replenish iron stores. 1, 2
• Do not assume all gastrointestinal symptoms are due to iron; persistent symptoms warrant medical evaluation for other causes. 1
• Do not take iron more than once daily (or every other day in your regimen), as multiple daily doses increase side effects without improving absorption due to hepcidin elevation. 1, 2