Abstract
This study was done to clarify the optimal number and type of casual urine specimens required to estimate urinary sodium/potassium (Na/K) ratio in individuals with high blood pressure. A total of 74 individuals with high blood pressure, 43 treated and 31 untreated, were recruited from the Japanese general population. Urinary sodium, potassium and Na/K ratio were measured in both casual urine samples and 7-day 24-h urine samples and then analyzed by correlation and Bland–Altman analyses. Mean Na/K ratio from random casual urine samples on four or more days strongly correlated with the Na/K ratio of 7-day 24-h urine (r=0.80–0.87), which was similar to the correlation between 1 and 2-day 24-h urine and 7-day 24-h urine (r=0.75–0.89). The agreement quality for Na/K ratio of seven random casual urine for estimating the Na/K ratio of 7-day 24-h urine was good (bias: −0.26, limits of agreements: −1.53–1.01), and it was similar to that of 2-day 24-h urine for estimating 7-day 24-h values (bias: 0.07, limits of agreement: −1.03 to 1.18). Stratified analyses comparing individuals using antihypertensive medication and individuals not using antihypertensive medication showed similar results. Correlations of the means of casual urine sodium or potassium concentrations with 7-day 24-h sodium or potassium excretions were relatively weaker than those for Na/K ratio. The mean Na/K ratio of 4–7 random casual urine specimens on different days provides a good substitute for 1–2-day 24-h urinary Na/K ratio for individuals with high blood pressure.
Highlights
Worldwide, reducing salt intake and increasing potassium intake are important measures to reduce blood pressure.[1]
We have found that the mean Na/K ratio of six random daytime casual urine samples showed a strong correlation with and good agreement with the mean 7-day 24-h urinary Na/K ratio in healthy Japanese participants, mainly in normotensive individuals.[24]
We found that in individuals with high blood pressure, assessment of 4–7 random samples of casual urine on different days provides a good estimate of an individual’s daily urinary Na/ K ratio, which was similar to that determined by 1–2-day 24-h urine collections
Summary
Worldwide, reducing salt intake and increasing potassium intake are important measures to reduce blood pressure.[1] Many guidelines for the prevention and treatment of hypertension recommend reduction of daily salt intake; for example, WHO guideline says o 5 g per day.[2,3,4,5,6] In spite of the rigorous campaigning and recommendations for salt restriction, a fairly large gap continues to exist between the recommended target levels and actual salt intake among populations.[7,8,9]. Previous findings show that awareness of salt restriction is not sufficient for actual salt reduction in individuals.[10,11] Effective monitoring of adherence to the recommended dietary salt and potassium intake in hypertensive patients and general populations requires development of a convenient, inexpensive and appropriate monitoring system that will make each individual aware of his or her salt intake level and support dietary improvement habits. The gold standard for estimating an individual’s daily salt intake and potassium intake is 24-h urine collection.[12,13,14,15,16] To estimate the true long-term sodium intake, 24-h urine collection expanded for several days provide more reliable estimate of a person’s salt consumption levels rather than single 24-h urine collection, as the day-to-day variation in sodium intake and its urine excretion are relatively high.[16,17] In addition, the sodium/potassium (Na/K) ratio in 24-h urine has been reported to be related to blood pressure in epidemiologic studies.[18,19,20,21,22] Recent data from the observational studies reviewed provide additional support for the Na/K ratio as a superior metric to either sodium or potassium alone in the evaluation of blood pressure outcomes and incident hypertension.[22,23] repeated 24-h urine collections are neither easy nor practical for patients at clinics or at home
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