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Int J Epidemiol. 2017 Oct 1;46(5):1564-1572. doi: 10.1093/ije/dyw287.

Estimating 24-h urinary sodium/potassium ratio from casual ('spot') urinary sodium/potassium ratio: the INTERSALT Study.

Author information

1
Department of Public Health, Shiga University of Medical Science, Shiga, Japan.
2
Research and Development Department, OMRON HEALTHCARE Co., Ltd, Kyoto, Japan.
3
Center for Epidemiologic Research in Asia, Shiga University of Medical Science, Shiga, Japan.
4
Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, UK.
5
Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.

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.

KEYWORDS:

24-h urine; Na/K ratio; casual urine; individual estimate; population estimate

PMID:
28039381
PMCID:
PMC5837629
DOI:
10.1093/ije/dyw287
[Indexed for MEDLINE]
Free PMC Article

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