In a patient with a ferritin level of 37 ng/mL and no anemia, should iron be repleted?

Yes, ferritin 37 ng/mL without anemia should be repleted with iron supplementation.

A ferritin of 37 ng/mL represents iron deficiency without anemia (IDNA) and warrants treatment, as this level falls below the diagnostic threshold of 45 ng/mL recommended by recent AGA guidelines and is associated with clinically significant symptoms including fatigue, impaired cognitive function, reduced exercise capacity, and diminished quality of life 1, 2.

Diagnostic Confirmation

Your patient meets criteria for iron deficiency without anemia:

• Ferritin 37 ng/mL is below the 45 ng/mL threshold 1
• No anemia present (hemoglobin within normal range)
• This represents depleted iron stores requiring repletion

Important caveat: If your patient has any inflammatory condition (infection, autoimmune disease, chronic disease), the ferritin may be falsely elevated. In such cases, check transferrin saturation, soluble transferrin receptor, or reticulocyte hemoglobin to confirm true iron status 1.

Why Treatment is Necessary

Iron deficiency without anemia is not a benign condition. Recent high-quality evidence demonstrates:

• Clinically meaningful fatigue that improves with iron repletion 2
• Impaired cognitive function and anxiety 2
• Reduced exercise capacity—in athletes, ferritin <50 μg/L causes measurable decreases in peak oxygen consumption that fully reverse with treatment 3
• Diminished quality of life across multiple domains 4

The 2024 AGA guideline explicitly states that "iron repletion is needed to improve quality of life" and notes that management considerations for iron deficiency without anemia are similar to those for iron-deficiency anemia 1.

Treatment Approach

First-Line: Oral Iron

Start with oral ferrous sulfate 325 mg daily or every other day 4:

• Take on an empty stomach for better absorption (though taking with meals is acceptable if better tolerated) 1
• Consider adding 500 mg vitamin C to enhance absorption 1
• Alternate-day dosing may improve tolerability with similar efficacy

When to Use IV Iron Instead

Switch to intravenous iron if 4:

• Oral iron intolerance (nausea, abdominal pain, constipation)
• Malabsorption conditions (celiac disease, post-bariatric surgery, atrophic gastritis)
• Chronic inflammatory conditions (IBD, CKD, heart failure)
• Ongoing blood loss
• Need for rapid repletion

Identify the Underlying Cause

While treating, investigate why iron deficiency developed:

• Menstrual history: Heavy or prolonged periods (most common in reproductive-age women) 4, 5
• Dietary assessment: Inadequate intake, vegetarian/vegan diet 6
• GI evaluation: Consider H. pylori testing, celiac screening; bidirectional endoscopy if indicated (particularly in men, postmenopausal women, or those with GI symptoms) 1, 5
• Medications: NSAIDs, proton pump inhibitors 4

Follow-Up Testing

Recheck ferritin 8-10 weeks after starting oral iron or 8-12 weeks after IV iron 6, 7:

• Target ferritin >30 ng/mL at minimum, ideally >50 ng/mL for athletes or those with high physiological demands 3
• If ferritin remains low despite treatment, consider IV iron or investigate for ongoing losses
• Patients with recurrent deficiency benefit from intermittent oral supplementation and monitoring every 6-12 months 6

Critical Pitfall to Avoid

Do not continue long-term daily iron supplementation once ferritin normalizes—this is potentially harmful and not recommended 6. Stop treatment when stores are replete, then monitor periodically and retreat only if deficiency recurs.

The evidence strongly supports treating your patient's ferritin of 37 ng/mL, as this represents true iron deficiency that will impair quality of life and function even without anemia 1, 2, 4.