Why is it important to check the urine albumin-to-creatinine ratio (ACR) in patients with Restless Legs Syndrome (RLS)?

Urine Albumin-to-Creatinine Ratio in Restless Legs Syndrome

Checking urine albumin-to-creatinine ratio (ACR) in patients with Restless Legs Syndrome (RLS) is important primarily to screen for chronic kidney disease (CKD), which is a common secondary cause of RLS and significantly impacts mortality and morbidity outcomes.

Connection Between RLS and Kidney Disease

Kidney disease, particularly end-stage renal disease (ESRD), is strongly associated with RLS for several reasons:

• Uremic RLS (RLS secondary to kidney disease) has a much higher prevalence (12-62%) compared to the general population (3-9%) 1
• RLS in dialysis patients is associated with:
  • Higher risk of cardiovascular events (64.5% with RLS vs. 39.1% without RLS) 1
  • Increased mortality (32.3% with RLS vs. 14.5% without RLS) 1
  • More severe symptoms requiring higher medication doses 2

Why Check ACR Specifically

1. Early Detection of Kidney Disease:

   • ACR is recommended as part of the laboratory evaluation for RLS to rule out secondary causes 3
   • European Urology guidelines specifically list urine ACR as part of the recommended testing for patients with suspected sleep disorders including RLS 4

2. Staging and Risk Assessment:

   • ACR helps classify CKD stages and assess progression risk 4
   • Even low levels of albuminuria are associated with increased cardiovascular and kidney disease risk 4
   • The combination of ACR and eGFR provides a more comprehensive assessment of kidney function and risk 4

3. Treatment Implications:

   • Patients with RLS and kidney disease require different treatment approaches:
     • Gabapentin is recommended as first-line for RLS patients with CKD or ESRD 3
     • Iron supplementation protocols differ for RLS patients with kidney disease 3

Clinical Approach to ACR Testing in RLS

When to Check ACR in RLS Patients:

• At initial evaluation of all patients with RLS symptoms 3
• Particularly important in patients with:
  • Risk factors for kidney disease (diabetes, hypertension)
  • Symptoms suggestive of more severe RLS (continuous symptoms vs. intermittent) 1
  • Poor response to standard RLS treatments 2

Interpreting ACR Results:

• Normal ACR: <30 mg/g creatinine 4
• Moderately increased: 30-299 mg/g creatinine 4
• Severely increased: >300 mg/g creatinine 4

Management Implications:

• If ACR is elevated:
  • Further kidney function evaluation is warranted (eGFR, complete workup)
  • Consider nephrology referral if ACR >300 mg/g or eGFR <30 mL/min/1.73m² 4
  • Adjust RLS treatment approach to account for kidney disease 3

Clinical Significance

The presence of albuminuria in RLS patients has significant implications:

1. Mortality Risk: RLS patients with kidney disease have significantly higher mortality (up to 55.6% in those with continuous RLS symptoms) 1

2. Cardiovascular Risk: RLS with kidney disease increases cardiovascular event risk by 64.5% compared to 39.1% in those without RLS 1

3. Treatment Resistance: Uremic RLS often requires higher medication doses and has decreased response to dopaminergic agonists 2

4. Disease Progression: Uremic RLS deteriorates faster and becomes more severe than idiopathic RLS 2

By identifying kidney disease through ACR testing in RLS patients, clinicians can implement appropriate treatment strategies that address both conditions and potentially reduce mortality and morbidity risks.