Patient with iron‑deficiency anemia on oral ferrous sulfate 325 mg daily now has ferritin 161 ng/mL (up from 123 ng/mL) and a modest rise in transferrin saturation, but the CBC still shows microcytic, hypochromic anemia; should I increase the iron dose, continue the same dose, or stop therapy?

Continue Current Oral Iron Dose and Reassess in 4-6 Weeks

Your patient's ferritin has risen appropriately from 123 to 161 ng/mL on oral iron 325 mg daily, indicating adequate iron absorption and store repletion; you should continue the same dose and allow more time for hemoglobin recovery, as complete correction of microcytic anemia typically lags behind ferritin normalization by 8-12 weeks. 1

Why Continue Rather Than Increase or Stop

Ferritin Response Indicates Adequate Therapy

• Your patient's ferritin increased from 123 to 161 ng/mL, demonstrating effective oral iron absorption 1
• Ferritin >100 ng/mL indicates adequate iron stores are being rebuilt 1
• The modest rise in TIBC (171→176) and transferrin (127→132) reflects improving iron availability 1

Hemoglobin Recovery Lags Behind Ferritin

• Complete correction of microcytic, hypochromic anemia requires 8-12 weeks of continuous iron therapy even after ferritin normalizes 1, 2
• Red blood cell indices (MCV, MCH) are the last parameters to normalize, often taking 3-4 months 1, 2
• The CBC showing persistent microcytosis/hypochromia at this early stage does not indicate treatment failure 1

Oral Iron Dosing Principles

• Effective iron repletion requires 100-200 mg elemental iron daily for 3-12 weeks 2
• Ferrous sulfate 325 mg contains approximately 65 mg elemental iron, which is appropriate first-line dosing 1
• Increasing the dose does not significantly improve absorption and increases gastrointestinal side effects 1, 2

When to Reassess Response

Timing of Follow-Up

• Recheck CBC, ferritin, and transferrin saturation at 8-10 weeks from initiation 1
• Expect hemoglobin rise of ≥1.0 g/dL by 4-8 weeks if responding adequately 1
• Do not check ferritin sooner, as levels may be falsely elevated during active supplementation 1

Criteria for Adequate Response

• Hemoglobin increase ≥1.0 g/dL from baseline 1
• Ferritin maintained >100 ng/mL 1
• Transferrin saturation >20% 1
• Gradual normalization of MCV and MCH over 8-12 weeks 1, 2

When to Consider IV Iron Instead

Indications for Switching to Intravenous Iron

• No hemoglobin rise (≥1.0 g/dL) after 8 weeks of adequate oral iron 1
• Ferritin fails to rise or remains <100 ng/mL despite compliance 1
• Severe anemia requiring rapid correction 1, 2
• Gastrointestinal intolerance preventing compliance 1, 2
• Malabsorption suspected (celiac disease, inflammatory bowel disease, atrophic gastritis) 1, 3

IV Iron Formulations and Dosing

• Ferric carboxymaltose or ferric derisomaltose allow 500-1000 mg in single 15-minute infusion 1, 2
• Iron sucrose limited to 200 mg per dose over 10 minutes 1, 2
• Calculate total iron deficit using Ganzoni formula or give empiric 1 gram total dose 1
• Monitor for hypophosphatemia with ferric carboxymaltose 2, 3

Common Pitfalls to Avoid

Do Not Stop Iron Prematurely

• Stopping iron when ferritin normalizes but before hemoglobin/MCV correct leads to relapse 1, 2
• Iron stores must be fully replenished to sustain erythropoiesis 1

Do Not Increase Oral Dose Unnecessarily

• Higher oral iron doses (>200 mg elemental iron daily) do not improve absorption 1, 2
• Increased dosing raises hepcidin levels, paradoxically reducing absorption 1
• Consider alternate-day dosing if gastrointestinal side effects develop 1

Rule Out Ongoing Blood Loss

• If no response by 8 weeks, investigate for occult gastrointestinal bleeding, menorrhagia, or other blood loss 1, 3
• Check for malabsorption causes: celiac serology, H. pylori, atrophic gastritis 1, 3
• Consider rare causes like TMPRSS6 mutations (iron-refractory iron deficiency anemia) if refractory to both oral and IV iron 1, 3

Monitor for Iron Overload

• Do not continue supplementation once hemoglobin, ferritin, and transferrin saturation normalize 1
• Avoid ferritin >500-800 ng/mL or transferrin saturation >50% to prevent toxicity 1