title: Validation and comparison of three formulae to estimate sodium and potassium excretion from a single morning fasting urine compared to 24-h measures in 11 countries.
abstract: OBJECTIVE
  Although 24-h urinary measure to estimate sodium and potassium excretion is the gold standard, it is not practical for large studies. We compared estimates of 24-h sodium and potassium excretion from a single morning fasting urine (MFU) using three different formulae in healthy individuals.
  
  
  METHODS
  We studied 1083 individuals aged 35-70 years from the general population in 11 countries. A 24-h urine and MFU specimen were obtained from each individual. A subset of 448 individuals repeated the measures after 30-90 days. The Kawasaki, Tanaka, and INTERSALT formulae were used to estimate urinary excretion from a MFU specimen.
  
  
  RESULTS
  The intraclass correlation coefficient (ICC) between estimated and measured sodium excretion was higher with Kawasaki (0.71; 95% confidence interval, CI: 0.65-0.76) compared with INTERSALT (0.49; 95% CI: 0.29-0.62) and Tanaka (0.54; 95% CI: 0.42-0.62) formulae (P <0.001). For potassium, the ICC was higher with the Kawasaki (0.55; 95% CI: 0.31-0.69) than the Tanaka (0.36; 95% CI: -0.07 to 0.60; P <0.05) formula (no INTERSALT formula exists for potassium). The degree of bias (vs. the 24-h urine) for sodium was smaller with Kawasaki (+313 mg/day; 95% CI: +182 to +444) compared with INTERSALT (-872 mg/day; 95% CI: -728 to -1016) and Tanaka (-548 mg/day; 95% CI: -408 to -688) formulae (P <0.001 and P = 0.02, respectively). Similarly for potassium, the Kawasaki formula provided the best agreement and least bias. Blood pressure correlated most closely and similarly with the 24-h and Kawasaki estimates for sodium compared with the other two formulae.
  
  
  CONCLUSIONS
  In a diverse population, the Kawasaki formula is the most valid and least biased method of estimating 24-h sodium excretion from a single MFU and is suitable for population studies.
authors.affiliation: aPopulation Health Research Institute, Hamilton Health Sciences bDepartment of Clinical Epidemiology and Biostatistics cDepartment of Medicine, McMaster University, Hamilton, Ontario, Canada dHRB-Clinical Research Facility, NUI Galway, Galway, Ireland eQuebec Heart Institute, Hospital Laval, Ste-Foy, Québec fDepartment of Medicine, University of Ottawa, Ottawa, Ontario gFaculty of Health Sciences, Simon Fraser University and Division of Cardiology, Providence Healthcare, Vancouver, British Columbia hDepartment of Laboratory Medicine, McMaster University, Hamilton iScience Integration Division, Public Health Agency of Canada, Ottawa, Ontario, Canada jNational Centre for Cardiovascular Diseases, Cardiovascular Institute and FuWai Hospital, Chinese Academy of Medical Sciences, Beijing, China kMarmara University Faculty of Health Sciences, Department of Health Management lYeditepe University Medical Faculty, Department of Family Medicine, Istanbul, Turkey mSt John's Medical College and Research Institute, Bangalore, India nHatta Hospital, Dubai Health Authority, Dubai, United Arab Emirates oFundacion Oftalmologica de Santander-FOSCAL, Floridablanca-Santander, Colombia pDante Pazzanese Institute of Cardiology, Sao Paulo, SP, Brazil qFaculty of Medicine, Universiti Teknologi MARA Sungai Buloh, Selangor, Malaysia rSahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden sFaculty of Health Sciences, North-West University, Potchefstroom Campus, Potchefstroom, South Africa tEstudios Clínicos Latinoamérica, Rosario, Argentina.
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authors.forename: Andrés
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authors.lastname: Orlandini
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authors.lastname: Rangarajan
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mesh_terms: D000328:Adult; D000368:Aged; D005215:Fasting; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000652:urine*; D012964:Sodium / Q000652:urine*
chemical_list: D012964:Sodium; D011188:Potassium