Cosinor-rhythmometry for 24-h urinary sodium, potassium, creatinine excretion in the Chinese adult population

Abstract

Background: The low accuracy of equations predicting 24-h urinary sodium excretion using a single spot urine sample contributed to the misclassification of individual sodium intake levels. The application of single spot urine sample is limited by a lack of representativity of urinary sodium excretion, possibly due to the circadian rhythm in urinary excretion. This study aimed to explore the circadian rhythm, characteristics, and parameters in a healthy young adult Chinese population as a theoretical foundation for developing new approaches. Methods: Eighty-five participants (mean age 32.4 years) completed the 24-h urine collection by successively collecting each of the single-voided specimens within 24 h. The concentrations of the urinary sodium, potassium, and creatinine for each voided specimen were measured. Cosinor analysis was applied to explore the circadian rhythm of the urinary sodium, potassium, and creatinine excretion. The excretion per hour was computed for analyzing the change over time with repeated-measures analysis of variance and a cubic spline model. Results: The metabolism of urinary sodium, potassium, and creatinine showed different patterns of circadian rhythm, although the urinary sodium excretion showed non-significant parameters in the cosinor model. A significant circadian rhythm of urinary creatinine excretion was observed, while the circadian rhythm of sodium was less significant than that of potassium. The circadian rhythm of urinary sodium and creatinine excretion showed synchronization to some extent, which had a nocturnal peak and fell to the lowest around noon to afternoon. In contrast, the peak of potassium was observed in the morning and dropped to the lowest point in the evening. The hourly urinary excretion followed a similar circadian rhythm. Conclusion: It is necessary to consider the circadian rhythm of urinary sodium, potassium, and creatinine excretion in adults while exploring the estimation model for 24-h urinary sodium excretion using spot urine.

Accuracy of equations for predicting 24-h urinary potassium excretion from spot urine samples in Chinese children

“…Compared with Masayuki Okuda's study in school-aged children and adolescents which developed equations using the ratios of Na/Cr, and K/Cr to estimate daily urinary Na and K excretion using first-morning spot urine (overnight urine) (36) , our research was hospital based, and the population characteristics of non-hospital-based studies, such as age and sex distributions, might lead to different proportion rates, even though the compliance and completeness of 24-hour urine collection might be better controlled in hospital-based populations. The variation of Tanaka formulas regarding to timing of spot urine were inconsistent Accepted manuscript between their study and ours, which may partly because of rhythm of 24-h urinary potassium between adults and children are different (37) , thus need more studies to figure out the reasons.…”

Evaluation of three prediction formulas of 24-hour urinary sodium excretion in Chinese residents: a systematic review and meta-analysis

“…Using spot urine samples could be a convenient alternative to 24-h urine collections for monitoring Na intake at the population level ( 26 , 32 ) . The three formulas in the meta-analyses all showed moderate correlations (0·36–0·43) between the estimated and measured 24hUNa, slightly lower than those observed in the Italian population (0·62–0·70) ( 33 ) and slightly higher than the Portuguese population (0·25–0·36) ( 34 ) .…”

Urinary Potassium and Kidney Function Decline in the Population—Observational Study

“…Urinary potassium was assessed as the ratio of urinary potassium concentration to urinary creatinine concentration to exclude the bias due to errors in completeness or timing of urine collection [ 34 ] and was used as the main independent variable (from here on abbreviated as uK/Cr). Exam-1 uK/Cr in spot samples and exam-2 uK/Cr in overnight collections were separately analyzed to control whether findings were affected by circadian rhythms in urinary potassium [ 35 , 36 ]. Serum potassium was used as index of extracellular potassium.…”