title: Spot urine sodium measurements do not accurately estimate dietary sodium intake in chronic kidney disease.
abstract: BACKGROUND
  Sodium intake influences blood pressure and proteinuria, yet the impact on long-term outcomes is uncertain in chronic kidney disease (CKD). Accurate assessment is essential for clinical and public policy recommendations, but few large-scale studies use 24-h urine collections. Recent studies that used spot urine sodium and associated estimating equations suggest that they may provide a suitable alternative, but their accuracy in patients with CKD is unknown.
  
  
  OBJECTIVE
  We compared the accuracy of 4 equations [the Nerbass, INTERSALT (International Cooperative Study on Salt, Other Factors, and Blood Pressure), Tanaka, and Kawasaki equations] that use spot urine sodium to estimate 24-h sodium excretion in patients with moderate to advanced CKD.
  
  
  METHODS
  We evaluated the accuracy of spot urine sodium to predict mean 24-h urine sodium excretion over 9 mo in 129 participants with stage 3-4 CKD. Spot morning urine sodium was used in 4 estimating equations. Bias, precision, and accuracy were assessed and compared across each equation.
  
  
  RESULTS
  The mean age of the participants was 67 y, 52% were female, and the mean estimated glomerular filtration rate was 31 ± 9 mL · min(-1) · 1.73 m(-2) The mean ± SD number of 24-h urine collections was 3.5 ± 0.8/participant, and the mean 24-h sodium excretion was 168.2 ± 67.5 mmol/d. Although the Tanaka equation demonstrated the least bias (mean: -8.2 mmol/d), all 4 equations had poor precision and accuracy. The INTERSALT equation demonstrated the highest accuracy but derived an estimate only within 30% of mean measured sodium excretion in only 57% of observations. Bland-Altman plots revealed systematic bias with the Nerbass, INTERSALT, and Tanaka equations, underestimating sodium excretion when intake was high.
  
  
  CONCLUSIONS
  These findings do not support the use of spot urine specimens to estimate dietary sodium intake in patients with CKD and research studies enriched with patients with CKD. The parent data for this study come from a clinical trial that was registered at clinicaltrials.gov as NCT00785629.
authors.affiliation: School of Medicine.
authors.forename: Carly E
authors.initials: CE
authors.lastname: Dougher
authors.affiliation: School of Medicine, Division of Nephrology-Hypertension, and Department of Family Medicine and Public Health, University of California San Diego, San Diego, CA; Veterans Affairs San Diego Healthcare System, San Diego, CA; and.
authors.forename: Dena E
authors.initials: DE
authors.lastname: Rifkin
authors.affiliation: School of Medicine, Department of Family Medicine and Public Health, University of California San Diego, San Diego, CA;
authors.forename: Cheryl Am
authors.initials: CA
authors.lastname: Anderson
authors.affiliation: Denver Nephrology, Denver, CO.
authors.forename: Gerard
authors.initials: G
authors.lastname: Smits
authors.affiliation: Denver Nephrology, Denver, CO.
authors.forename: Martha S
authors.initials: MS
authors.lastname: Persky
authors.affiliation: Denver Nephrology, Denver, CO.
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Block
authors.affiliation: School of Medicine, Division of Nephrology-Hypertension, and Department of Family Medicine and Public Health, University of California San Diego, San Diego, CA; Veterans Affairs San Diego Healthcare System, San Diego, CA; and joeix@ucsd.edu.
authors.forename: Joachim H
authors.initials: JH
authors.lastname: Ix
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000652:urine; D001794:Blood Pressure; D004032:Diet; D005247:Feeding Behavior; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000503:physiopathology; D008297:Male; D055641:Mathematical Concepts; D008875:Middle Aged; D051436:Renal Insufficiency, Chronic / Q000652:urine*; D015203:Reproducibility of Results; D012964:Sodium / Q000008:administration & dosage / Q000652:urine*; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage / Q000652:urine; D012982:Sodium, Dietary / Q000008:administration & dosage / Q000652:urine*; D016482:Urinalysis
chemical_list: D015415:Biomarkers; D017673:Sodium Chloride, Dietary; D012982:Sodium, Dietary; D012964:Sodium
keywords: 24-hour urine; cardiovascular disease; chronic kidney disease; hypertension; sodium intake; spot urine