What is the management approach for an adult patient with iron deficiency anemia due to low ferritin levels?

Management of Low Ferritin in Adults

Start oral iron supplementation with one tablet daily of ferrous sulfate (325 mg), ferrous fumarate, or ferrous gluconate, and simultaneously investigate the underlying cause through detailed history, urinalysis, celiac disease screening, and bidirectional endoscopy in men and postmenopausal women. 1, 2

Diagnostic Confirmation

Before initiating treatment, confirm iron deficiency with appropriate testing:

• Serum ferritin <15 μg/L is highly specific for iron deficiency (specificity 0.99) and diagnostic of absent iron stores 1
• Ferritin <30 μg/L generally indicates low body iron stores in otherwise healthy adults 1, 3
• Ferritin <45 μg/L provides optimal sensitivity-specificity trade-off (specificity 0.92) and warrants investigation, especially with concurrent inflammation 1
• In patients with inflammation, ferritin may be falsely elevated; consider transferrin saturation <20% as an additional marker 1, 2, 4
• Ferritin >100-150 μg/L makes absolute iron deficiency unlikely, even with inflammation 1

Important caveat: Ferritin is an acute phase protein, so apparently normal levels (15-100 μg/L) can occur with iron deficiency in inflammatory conditions. 1

Immediate Treatment Approach

First-Line: Oral Iron Therapy

Begin treatment immediately without waiting for investigation results unless colonoscopy is imminent: 1

• Ferrous sulfate 325 mg once daily (or ferrous fumarate/gluconate equivalent) 1, 2, 4
• Alternate-day dosing improves absorption and may reduce gastrointestinal side effects 1, 2
• Use preparations with 28-50 mg elemental iron to minimize side effects while maintaining efficacy 3
• Monitor hemoglobin response within 2-4 weeks: expect Hb rise ≥10 g/L within 2 weeks if true iron deficiency 1, 2
• Continue treatment for 8-10 weeks, then recheck ferritin and hemoglobin 1, 3

If oral iron not tolerated: Consider reduced dose (one tablet every other day) or switch to alternative oral preparations before considering parenteral iron 1

Investigation of Underlying Cause

Essential Initial Workup (All Patients)

• Detailed history focusing on:

  • Menstrual blood loss in premenopausal women 1
  • Dietary intake (vegetarian/vegan diet, eating disorders) 1, 3
  • NSAID/aspirin use 1
  • Gastrointestinal symptoms 1
  • Family history of GI pathology, bleeding disorders, or hemoglobinopathies 1

• Urinalysis or urine microscopy to exclude renal blood loss 1

• Celiac disease screening (serology or small bowel biopsy at gastroscopy) - found in 3-5% of IDA cases 1

Endoscopic Investigation

Men and postmenopausal women: Bidirectional endoscopy (gastroscopy and colonoscopy) is first-line investigation 1, 2

• Upper GI endoscopy reveals pathology in 30-50% of cases 1
• Always obtain small bowel biopsies during gastroscopy to screen for celiac disease 1
• Dual pathology (upper and lower GI lesions) occurs in ~10% of cases 1
• CT colonography is reasonable alternative if colonoscopy not suitable 1

Premenopausal women: GI investigation generally not warranted for non-anemic iron deficiency in absence of GI symptoms, family history, or other concerning features, as menstrual blood loss is likely cause 1

If initial endoscopy negative and inadequate response to iron or recurrent IDA:

• Capsule endoscopy is preferred test for small bowel examination (highly sensitive for mucosal lesions) 1
• CT/MR enterography as complementary investigation for inflammatory/neoplastic disease 1

Indications for Intravenous Iron

Consider IV iron when: 1, 2, 4

• Oral iron intolerance or gastrointestinal side effects (~50% of patients experience reduced adherence) 2
• Inadequate response to oral therapy after 2-4 weeks 1, 2
• Malabsorption (celiac disease, post-bariatric surgery, inflammatory bowel disease) 2, 4
• Chronic inflammatory conditions (heart failure, chronic kidney disease, IBD, cancer) 2, 4
• Ongoing blood loss 2, 4
• Second and third trimesters of pregnancy 2, 4
• Need for rapid iron repletion (e.g., preoperative patient blood management) 1

Preferred formulations: Ferric carboxymaltose, ferumoxytol, iron isomaltoside (allow rapid administration of large single doses with low risk) 1

Safety note: Hypersensitivity reactions are rare (<1:250,000 with recent formulations) but can be life-threatening; avoid high molecular weight iron dextran 1, 2

Long-Term Management

• Recheck iron studies 8-10 weeks after treatment initiation (not earlier after IV iron as ferritin falsely elevated) 1, 3
• Long-term maintenance iron therapy may be appropriate when cause is unknown or irreversible 1
• Patients with recurrent low ferritin benefit from intermittent oral supplementation 3
• Monitor every 6-12 months in patients requiring long-term therapy 3

Critical warning: Do not supplement iron when ferritin is normal or elevated (>100-150 μg/L) - this is inefficient, causes side effects, and is potentially harmful 1, 3, 4