How should restless‑legs syndrome be managed in a patient with a ferritin level of 89 µg/L and a transferrin saturation of 25%?

Management Recommendation for RLS with Ferritin 89 µg/L and Transferrin Saturation 25%

This patient should receive iron supplementation, with intravenous ferric carboxymaltose (1000 mg) being the preferred first-line treatment option, followed by initiation of gabapentinoid therapy if symptoms persist after addressing iron deficiency. 1

Iron Status Assessment and Treatment Decision

Your patient's iron parameters fall within the treatment threshold established by the 2025 AASM guidelines:

• Ferritin 89 µg/L: Falls between 75-100 µg/L, the range where IV iron is specifically recommended
• Transferrin saturation 25%: Above the 20% threshold but below the optimal 35% level associated with better treatment response

The 2025 AASM guidelines explicitly state that iron supplementation should be instituted with IV iron when serum ferritin is between 75 and 100 ng/mL 1. This represents a critical update from older guidelines and reflects emerging understanding that brain iron deficiency in RLS requires more aggressive repletion than general population iron deficiency.

Specific Iron Treatment Algorithm

First-Line: Intravenous Iron

Administer IV ferric carboxymaltose 1000 mg (strong recommendation, moderate certainty of evidence) 1

• This receives the highest level recommendation for iron therapy in RLS
• Multiple RCTs demonstrate clinically significant reduction in IRLS scores
• Approximately 65-70% of patients show meaningful improvement
• Recent evidence suggests efficacy even with ferritin levels up to 300 µg/L 2

Alternative IV formulations if ferric carboxymaltose unavailable:

• IV low molecular weight iron dextran (conditional recommendation) 1
• IV ferumoxytol (conditional recommendation) 1

Second-Line: Oral Iron (if IV not accessible)

Ferrous sulfate 325-650 mg daily or every other day (conditional recommendation, moderate certainty) 1

• Less effective than IV iron due to poor absorption when ferritin >50-75 µg/L
• Limited by gastrointestinal side effects (constipation)
• Should be taken with vitamin C to enhance absorption
• Consider this only if IV iron is not feasible due to access or reimbursement issues

Critical Caveat About Transferrin Saturation

Your patient's transferrin saturation of 25% is actually a favorable prognostic indicator. Recent research demonstrates that TSAT ≤35% predicts better response to IV iron therapy 3, 4. Specifically, lower TSAT values (particularly in females) correlate with higher response rates to IV ferric carboxymaltose, with odds ratios showing each percentage point increase in TSAT reduces response likelihood 4.

Pharmacologic Therapy After Iron Optimization

First-Line Medications (Strong Recommendations)

Once iron status is addressed, if symptoms require pharmacologic management:

Gabapentinoids - all receive strong recommendations 1:

1. Gabapentin enacarbil (preferred for consistent absorption)
2. Gabapentin
3. Pregabalin

Approximately 70% of patients achieve much or very much improved symptoms versus 40% with placebo 5.

Avoid Dopamine Agonists as First-Line

The 2025 guidelines represent a major shift: dopamine agonists (pramipexole, ropinirole, rotigotine) now receive conditional recommendations AGAINST standard use 1. This reverses previous practice due to:

• 7-10% annual incidence of augmentation (iatrogenic worsening)
• Long-term adverse effects outweigh short-term symptom benefits
• Should only be considered if patients prioritize immediate symptom relief over long-term safety

Important Pitfalls to Avoid

1. Don't wait for ferritin <75 µg/L: Your patient at 89 µg/L qualifies for IV iron specifically
2. Don't use oral iron as equivalent to IV: Absorption is inadequate at this ferritin level
3. Don't start dopamine agonists first: Gabapentinoids are now preferred initial pharmacotherapy
4. Don't ignore assay variability: Ferritin measurements vary by manufacturer; Roche assays read ~58% higher than Beckman 6. If using Roche, the equivalent cutoff for 100 µg/L is actually 158 µg/L
5. Don't combine gabapentinoids with opioids initially: Enhanced respiratory depression risk, especially with untreated sleep apnea 1

Before Initiating Treatment

Address exacerbating factors:

• Discontinue antihistamines (diphenhydramine), serotonergic antidepressants, dopamine antagonists if possible
• Screen for and treat obstructive sleep apnea
• Reduce alcohol and caffeine intake 1

Monitoring and Follow-Up

• Reassess symptoms 4 weeks after IV iron administration
• Recheck iron studies (ferritin, TSAT) at 4 weeks post-treatment
• If inadequate response despite iron repletion, initiate gabapentinoid therapy
• Consider repeat IV iron dosing if ferritin drops below threshold (protocols still being standardized)

This patient's iron parameters place them squarely in the evidence-based treatment zone for IV iron, which should be the immediate priority before considering other pharmacologic interventions.