Estimating 24-hour urinary sodium/potassium ratio from casual (“spot”) urinary sodium/potassium ratio: The INTERSALT Study

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Title: Estimating 24-hour urinary sodium/potassium ratio from casual (“spot”) urinary sodium/potassium ratio: The INTERSALT Study
Authors: Iwahori, T
Miura, K
Ueshima, H
Chan, Q
Dyer, AR
Elliott, P
Stamler, J
Item Type: Journal Article
Abstract: Background: 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. Methods: 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. Results: 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. Conclusion: 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.
Issue Date: 30-Dec-2016
Date of Acceptance: 9-Sep-2016
ISSN: 1464-3685
Publisher: Oxford University Press (OUP)
Start Page: 1564
End Page: 1572
Journal / Book Title: International Journal of Epidemiology
Volume: 46
Issue: 5
Replaces: 10044/1/42791
Copyright Statement: © The Author 2016. Published by Oxford University Press on behalf of the International Epidemiological Association. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Sponsor/Funder: National Institute for Health Research
Imperial College Healthcare NHS Trust- BRC Funding
Medical Research Council (MRC)
National Institute for Health Research
Funder's Grant Number: NF-SI-0611-10136
RDC01 79560
Keywords: Science & Technology
Life Sciences & Biomedicine
Public, Environmental & Occupational Health
Na/K ratio
casual urine
24-h urine
population estimate
individual estimate
INTERSALT Research Group
0104 Statistics
1117 Public Health And Health Services
Publication Status: Published
Open Access location:
Appears in Collections:Faculty of Medicine
Epidemiology, Public Health and Primary Care

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