title: Estimating 24-h urinary sodium/potassium ratio from casual ('spot') urinary sodium/potassium ratio: the INTERSALT Study.
abstract: Association between casual and 24-h urinary sodium-to-potassium (Na/K) ratio is well recognized, although it has not been validated in diverse demographic groups. Our aim was to assess utility across and within populations of casual urine to estimate 24-h urinary Na/K ratio using data from the INTERSALT Study.
  
  
  
  The INTERSALT Study collected cross-sectional standardized data on casual urinary sodium and potassium and also on timed 24-h urinary sodium and potassium for 10 065 individuals from 52 population samples in 32 countries (1985-87). Pearson correlation coefficients and agreement were computed for Na/K ratio of casual urine against 24-h urinary Na/K ratio both at population and individual levels.
  
  
  
  Pearson correlation coefficients relating means of 24-h urine and casual urine Na/K ratio were r = 0.96 and r = 0.69 in analyses across populations and individuals, respectively. Correlations of casual urine Na/creatinine and K/creatinine ratios with 24-h urinary Na and K excretion, respectively, were lower than correlation of casual and 24-h urinary Na/K ratio in analyses across populations and individuals. The bias estimate with the Bland-Altman method, defined as the difference between Na/K ratio of 24-h urine and casual urine, was approximately 0.4 across both populations and individuals. Spread around, the mean bias was higher for individuals than populations.
  
  
  
  With appropriate bias correction, casual urine Na/K ratio may be a useful, low-burden alternative method to 24-h urine for estimation of population urinary Na/K ratio. It may also be applicable for assessment of the urinary Na/K ratio of individuals, with use of repeated measurements to reduce measurement error and increase precision.
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Shiga, Japan.|Research and Development Department, OMRON HEALTHCARE Co., Ltd, Kyoto, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Iwahori
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Shiga, Japan.|Center for Epidemiologic Research in Asia, Shiga University of Medical Science, Shiga, Japan.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Miura
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Shiga, Japan.|Center for Epidemiologic Research in Asia, Shiga University of Medical Science, Shiga, Japan.
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Ueshima
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, UK.
authors.forename: Queenie
authors.initials: Q
authors.lastname: Chan
authors.affiliation: Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Dyer
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Elliott
authors.affiliation: Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
authors.forename: Jeremiah
authors.initials: J
authors.lastname: Stamler
mesh_terms: D000328:Adult; D003404:Creatinine / Q000652:urine*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D038622:Internationality; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000652:urine*; D012964:Sodium / Q000652:urine*; D059349:Urine Specimen Collection / Q000379:methods; D055815:Young Adult
chemical_list: D012964:Sodium; D003404:Creatinine; D011188:Potassium
keywords: 24-h urine; Na/K ratio; casual urine; individual estimate; population estimate