Iron status and chronic kidney disease predict restless legs syndrome in an older hospital population

BackgroundIron deficiency is important in the pathogenesis of restless legs syndrome (RLS), and serum ferritin measurement, using a cutoff of 45–50 ng/ml, is widely recommended as the optimal screening test for iron deficiency in RLS. Serum ferritin often increases with inflammation, and a higher cutoff may be better in those with acute and chronic inflammatory conditions, including those with chronic kidney disease (CKD).MethodsThe relationships between RLS and potential secondary causes were examined in hospital patients aged 50 years or more. Diagnosis of RLS was based on a clinician interview.ResultsOf 301 patients, 55 (18.3%) had RLS. Ferritin levels less than 40 ng/ml and between 40 and 69 ng/ml and Stage 4 CKD (estimated glomerular filtration rate [eGFR] between 15 and 29 ml/min and not on dialysis) were associated with significantly higher odds for RLS in univariate and multivariate analyses.ConclusionIron deficiency and chronic kidney disease are the strongest predictors of RLS in older hospital patients. Ferritin less than 70 ng/ml is the best cutoff for identifying possible iron deficiency in RLS patients with inflammatory conditions. Independent of iron status, RLS is strongly associated with chronic kidney disease that is not severe enough to require dialysis, and the results of this study suggest that eGFR values and stages of CKD should be reported in future studies of RLS.