What is the appropriate evaluation and management for a patient with iron‑deficiency anemia and low ferritin?

Management of Iron Deficiency Anemia with Low Ferritin

Start oral ferrous sulfate 325 mg daily (or every other day for better tolerance) as first-line therapy, and switch to intravenous iron if hemoglobin fails to increase by 1 g/dL within 2 weeks or if oral iron is not tolerated. 1

Diagnostic Confirmation

• Ferritin <45 ng/mL confirms iron deficiency in patients without inflammation, providing 85% sensitivity and 92% specificity 1
• For patients with chronic inflammatory conditions (CKD, heart failure, IBD), use ferritin <100 ng/mL as the diagnostic threshold 2
• Add transferrin saturation <20% when ferritin is 46-99 ng/mL to confirm the diagnosis 2
• Check C-reactive protein to exclude false-negative results from inflammation artificially elevating ferritin 3

Identifying the Underlying Cause

In postmenopausal women and men with iron deficiency anemia, perform bidirectional endoscopy (EGD and colonoscopy) at the same setting to identify gastrointestinal blood loss, as this represents a strong AGA recommendation. 1

• Recurrent blood loss accounts for 94% of iron deficiency anemia cases 2
• Test for Helicobacter pylori infection and celiac disease noninvasively, as both commonly cause iron deficiency anemia 2
• In younger menstruating women with heavy menstrual bleeding and no alarm symptoms, treat the bleeding source and provide iron supplementation without immediate endoscopy 2
• Consider malabsorption causes: atrophic gastritis, celiac disease, post-bariatric surgery, and IBD 4

Oral Iron Therapy (First-Line)

Prescribe ferrous sulfate 325 mg once daily, which contains approximately 65 mg elemental iron. 1

• Take iron once daily only—hepcidin remains elevated for 48 hours after each dose, blocking further absorption and increasing side effects without benefit 1
• Consider every-other-day dosing to improve tolerance and absorption, though this requires further study 1, 2
• Take on an empty stomach with 80-500 mg vitamin C (ascorbic acid) to enhance absorption 1
• Avoid tea and coffee within 1 hour of iron intake, as they powerfully inhibit absorption 1
• Alternative formulations (ferrous fumarate, ferrous gluconate, ferrous bisglycinate) have no proven superiority but may be tried if side effects occur 1
• Common side effects: constipation (12%), diarrhea (8%), nausea (11%)—these cause decreased adherence in approximately 50% of patients 1, 2

Monitoring Response to Oral Iron

Reassess hemoglobin after 2 weeks—it should increase by 1 g/dL. 1

• Check ferritin after 1 month—it should show reasonable increase 1
• If these parameters are not met despite adherence, switch to intravenous iron 1
• Repeat complete evaluation at 8-10 weeks to measure treatment success 3

Intravenous Iron Therapy (Second-Line or Specific Indications)

Use IV iron when oral iron fails, is not tolerated, or in specific clinical situations requiring rapid or reliable repletion. 1

Specific indications for IV iron:

• Oral iron intolerance or non-adherence 1, 4
• Impaired absorption: post-bariatric surgery, active IBD, celiac disease 1, 4
• Chronic inflammatory conditions: CKD, heart failure, IBD, cancer 1, 4
• Ongoing blood loss exceeding oral iron absorption capacity 1, 4
• Second and third trimesters of pregnancy 4
• Heart failure patients with iron deficiency—IV iron increases exercise capacity 2

IV iron administration:

• Choose formulations allowing 1-2 infusions to replace total iron deficit 1
• True allergic reactions are very rare (approximately 1:200,000 for major reactions) 1
• Most reactions are complement activation-related pseudo-allergy, not true allergy 1
• For mild reactions: stop infusion, restart after 15 minutes at slower rate 1
• For severe reactions: use corticosteroids; avoid diphenhydramine as side effects mimic worsening reactions 1
• Monitor for hypersensitivity (rare with newer formulations, <1%), hypophosphatemia/osteomalacia, and iron overload 5

Common Pitfalls to Avoid

• Do not prescribe iron more than once daily—this increases side effects without improving absorption due to hepcidin elevation 1
• Do not use ferritin <15 ng/mL as the diagnostic threshold—this misses 41% of iron deficiency cases 1
• Do not delay endoscopy in postmenopausal women or men—gastrointestinal malignancy must be excluded 1
• Do not continue oral iron indefinitely if hemoglobin fails to rise by 1 g/dL in 2 weeks—switch to IV iron 1
• Do not provide long-term iron supplementation when ferritin normalizes—this is potentially harmful 3