In a patient with restless legs syndrome and a ferritin level of 63 ng/mL (reference range 15–150 ng/mL), should iron supplementation be initiated?

Yes, treat with iron supplementation - your patient's ferritin of 63 ng/mL is below the threshold for RLS management.

In adults with restless legs syndrome, iron supplementation should be initiated when serum ferritin is ≤75 ng/mL, with a target goal above 100 ng/mL. 1 Your patient's ferritin of 63 ng/mL falls well below this threshold and warrants treatment.

Iron Supplementation Approach

The 2025 American Academy of Sleep Medicine guidelines establish RLS-specific iron parameters that differ substantially from general population guidelines 1:

• Treat when ferritin is between 75-100 ng/mL (not just when frankly deficient)
• Target ferritin >100 ng/mL
• This is a disease-specific recommendation unique to RLS pathophysiology

Treatment Options (in order of strength)

First-line: Intravenous Iron

IV ferric carboxymaltose (1000 mg) is the strongest recommendation for adults with RLS and appropriate iron status 1. This provides:

• Strong recommendation with moderate certainty of evidence
• Significant reduction in RLS severity scores
• More reliable absorption than oral formulations

Alternative IV options include low molecular weight iron dextran or ferumoxytol (conditional recommendations) 1.

Second-line: Oral Iron

Ferrous sulfate (325-650 mg daily or every other day) is suggested for patients with appropriate iron status 1, 2. This carries:

• Conditional recommendation with moderate certainty of evidence
• Lower efficacy due to absorption limitations
• Reasonable first approach if IV access is problematic

Critical Considerations

Check transferrin saturation alongside ferritin - iron therapy is particularly indicated when TSAT <20% 1. Recent evidence suggests TSAT ≤35% may be a more sensitive predictor of treatment response than ferritin alone 3.

Assay variability matters: Ferritin measurements differ significantly between manufacturers 4. A Beckman assay reading of 75 ng/mL equals approximately 121 ng/mL on Roche assay. Know which assay your lab uses and adjust thresholds accordingly to avoid undertreating patients.

Before Starting Pharmacologic Therapy

Address exacerbating factors first 1:

• Discontinue antihistamines (diphenhydramine), serotonergic antidepressants, and antidopaminergic medications
• Reduce alcohol and caffeine
• Evaluate for untreated sleep apnea

If Iron Therapy Fails

Only after optimizing iron status should you consider:

1. Gabapentin, gabapentin enacarbil, or pregabalin (strong recommendations, first-line pharmacotherapy) 1
2. Avoid dopamine agonists as standard therapy - they carry 7-10% annual risk of augmentation (iatrogenic worsening) 2

Common Pitfall

Do not wait for ferritin to drop into the "deficient" range by general medicine standards. RLS requires higher brain iron stores than other tissues - the 75-100 ng/mL threshold reflects this neurological need, not systemic iron deficiency 1, 5.

Your patient is correct that ferritin below 75 ng/mL can cause RLS symptoms. Treat now with either IV ferric carboxymaltose 1000 mg or oral ferrous sulfate 325 mg daily/every other day, targeting ferritin >100 ng/mL.