Validity of predictive equations for 24-h urinary potassium excretion based on timing of spot urine collection among adults: the MESA and CARDIA Urinary Sodium Study and NHANES Urinary Sodium Calibration Study

Diet and Other Modifiable Factors in Long-Term Decline of Kidney Function: Observational and Population-Based Cohort Study

BACKGROUND

Lower physical activity, lower alcohol intake, higher protein intake, higher sodium intake, and lower potassium intake related to greater kidney function decline over time, according to previous studies. The present study aimed to analyze the cumulative effects of these factors.

METHODS

This prospective, observational, population-based cohort study included 3039 adult examinees of the Gubbio study who participated in the baseline exam and 15-year follow-up exam. Kidney function was evaluated as estimated glomerular filtration rate (eGFR). Habitual physical activity in leisure time and habitual alcohol intake were assessed by questionnaires; dietary intakes of protein, sodium, and potassium were assessed by urinary markers. Based on previous reports, each one of the five modifiable factors was scored 0 for the tertile associated with smaller eGFR decline (low risk), 2 for the tertile associated with greater eGFR decline (high risk), and 1 for the intermediate tertile (intermediate risk). A cumulative score was calculated as the sum of the factor-specific scores and used as the main independent variable.

RESULTS

The cumulative score ranged from 0 to 10, that is, from low risk for all factors to high risk for all factors (skewness = 0.032, mean ± SD = 5 ± 2). To avoid the bias of low-n analyses, score 0 was re-coded as 1 and score 10 was recoded as 9; after re-coding, the cumulative score ranged from 1 to 9 (skewness = 0.016, mean ± SD = 5 ± 2). The cumulative score related to annualized eGFR change in multi-variable linear regression (slope = -0.027, 95%CI = -0.039/-0.014, p < 0.001); findings were consistent in apparently healthy examinees and other subgroups. De novo incidence of eGFR < 60 mL/min × 1.73 m2 was higher along the cumulative score (p < 0.001). Compared to score 1 (n examinees = 35, adjusted incidence = 2.0%), incidence of low kidney function was 4.5 times higher in score 5 (n examinees = 624, adjusted incidence = 8.9%) and 6.5 times higher in score 9 (n examinees = 86, adjusted incidence = 12.9%). The cumulative score related to incidence of low kidney function in multi-variable logistic regression (odds ratio = 1.19, 95%CI = 1.08/1.32, p < 0.001).

CONCLUSIONS

The combination of five modifiable factors predicted large differences in long-term incidence of low kidney function.

A Method for Estimating 24 h Urinary Sodium and Potassium Excretion by Spot Urine Specimen in Stroke Patients

Spot urine specimens have been used to estimate 24 h urinary sodium (Na) excretion (24UNaV) and potassium (K) excretion (24UKV). However, the validity is limited for 24UNaV and unknown for 24UKV in stroke patients, using the existing formulas. Herein, we developed and validated a new formula for 24UNaV and 24UKV by spot urine specimens in stroke patients. Spot and 24 h urine samples were collected from 970 stroke patients. The models of 24UNaV and 24UKV were developed using stepwise multivariate linear regression in 689 patients. The performance of different formulas was internally validated in 281 patients at the population and individual levels. The obtained new formulas were: (1) estimated 24UNaV (mmol/day): -0.191 × Age + 4.349 × BMI + 0.229 × Spot_Na + 1.744 × Spot_Na/Spot creatinine (Cr) + 41.492 (for male); -1.030 × Age + 2.011 × BMI + 0.143 × Spot_Na + 1.035 × Spot_Na/Spot_Cr + 147.159 (for female); and (2) estimated 24UKV (mmol/day): -0.052 × Age + 0.410 × BMI + 0.031 × Spot_K + 33.280 × Ln (spot_K/spot _Cr) - 5.789 × Ln (spot_Na/spot _Cr) - 1.035 (for male); -0.235 × Age + 0.530 × BMI + 0.040 × Spot_K + 30.990 × Ln (spot _K/spot _Cr) - 7.837 × Ln (spot_Na/spot_Cr) + 4.318 (for female). The new formula obtained the lowest mean bias (5.17 mmol/day for 24UNaV and 0.85 mmol/day for 24UKV) and highest proportion at the cutoff under the ±30% level for the estimation of 24UNaV (59.43%) and 24UKV (70.11%). The new formula provides a meaningful exploration to estimate 24UNaV and 24UKV in stroke patients by using spot urine specimens.

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

Accurate assessments of potassium intake in children are important for the early prevention of CVD. Currently, there is no simple approach for accurate estimation of potassium intake in children. We aim to evaluate the accuracy of 24-h urinary potassium excretion (24UKV) estimation in children using three common equations: the Kawasaki, Tanaka and Mage formulas, in a hospital-based setting. A total of 151 participants aged 5-18 years were initially enrolled, and spot urine samples were collected in the whole 24-h duration to measure the concentrations of potassium and creatinine. We calculated the mean difference, absolute and relative difference and misclassification rate between measured 24UKV and the predicted ones using Kawasaki, Tanaka and Mage formulas in 129 participants. The mean measured 24UKV was 1193·3 mg/d in our study. Mean differences between estimated and measured 24UKV were 1215·6, -14·9 and 230·3 mg/d by the Kawasaki, Tanaka and Mage formulas, respectively. All estimated 24UKV were significantly different from the measured values in all the time point (all P < 0·05), except for the predicted values from Tanaka formula using morning, afternoon and evening spot urine. The proportions with relative differences over 40 % were 87·2%, 32·5% and 47·3 % for Kawasaki, Tanaka and Mage formulas, respectively. Misclassification rates were 91·5 % for Kawasaki, 44·4 % for Tanaka and 58·9 % for Mage formula at the individual level. Our findings showed that misclassification could occur on the individual level when using Kawasaki, Tanaka and Mage formulas to estimate 24UKV from spot urine in the child population.

Estimating 24-Hour Urinary Excretion of Sodium and Potassium Is More Reliable from 24-Hour Urine Than Spot Urine Sample in a Feeding Study of US Older Postmenopausal Women

BACKGROUND

Assessing estimated sodium (Na) and potassium (K) intakes derived from 24-h urinary excretions compared with a spot urine sample, if comparable, could reduce participant burden in epidemiologic and clinical studies.

OBJECTIVES

In a 2-week controlled-feeding study, Na and K excretions from a 24-h urine collection were compared with a first-void spot urine sample, applying established algorithms and enhanced models to estimate 24-h excretion. Actual and estimated 24-h excretions were evaluated relative to mean daily Na and K intakes in the feeding study.

METHODS

A total of 153 older postmenopausal women ages 75.4 ± 3.5 y participated in a 2-wk controlled-feeding study with a 4-d repeating menu cycle based on their usual intake (ClinicalTrials.gov Identifier: NCT00000611). Of the 150 participants who provided both a first-void spot urine sample and a 24-h urine collection on the penultimate study day, statistical methods included Pearson correlations for Na and K between intake, 24-h collections, and the 24-h estimated excretions using 4 established algorithms: enhanced biomarker models by regressing ln-transformed intakes on ln-transformed 24-h excretions or ln-transformed 24-h estimated excretions plus participant characteristics and sensitivity analyses for factors potentially influencing Na or K excretion (e.g., possible kidney disease estimated glomerular filtration rate <60 mL/min/1.73 m2 ).

RESULTS

Pearson correlation coefficients between Na and K intakes and actual 24-h excretions were 0.57 and 0.38-0.44 for estimated 24-h excretions, depending on electrolyte and algorithm used. Enhanced biomarker model cross-validated R 2 (CVR2) for 24-h excretions were 38.5% (Na), 40.2% (K), and 42.0% (Na/K). After excluding participants with possible kidney disease, the CVR2 values were 43.2% (Na), 40.2% (K), and 38.1% (Na/K).

CONCLUSIONS

Twenty-four-hour urine excretion measurement performs better than estimated 24-h excretion from a spot urine as a biomarker for Na and K intake among a sample of primarily White postmenopausal women.

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

Background-Some data suggest favorable effects of a high potassium intake on kidney function. The present population-based study investigated cross-sectional and longitudinal relations of urinary potassium with kidney function. Methods-Study cohort included 2027 Gubbio Study examinees (56.9% women) with age ≥ 18 years at exam-1 and with complete data on selected variables at exam-1 (1983-1985), exam-2 (1989-1992), and exam-3 (2001-2007). Urinary potassium as urinary potassium/creatinine ratio was measured in daytime spot samples at exam-1 and in overnight timed collections at exam-2. Estimated glomerular filtration rate (eGFR) was measured at all exams. Covariates in analyses included demographics, anthropometry, blood pressure, drug treatments, diabetes, smoking, alcohol intake, and urinary markers of dietary sodium and protein. Results-In multivariable regression, urinary potassium/creatinine ratio cross-sectionally related to eGFR neither at exam-1 (standardized coefficient and 95%CI = 0.020 and -0.059/0.019) nor at exam-2 (0.024 and -0.013/0.056). Exam-1 urinary potassium/creatinine ratio related to eGFR change from exam-1 to exam-2 (0.051 and 0.018/0.084). Exam-2 urinary potassium/creatinine ratio related to eGFR change from exam-2 to exam-3 (0.048 and 0.005/0.091). Mean of urinary potassium/creatinine ratio at exam-1 and exam-2 related to eGFR change from exam-1 to exam-3 (0.056 and 0.027/0.087) and to incidence of eGFR < 60 mL/min per 1.73 m² from exam-1 to exam-3 (odds ratio and 95%CI = 0.78 and 0.61/0.98). Conclusion-In the population, urinary potassium did not relate cross-sectionally to eGFR but related to eGFR decline over time. Data support the existence of favorable effects of potassium intake on ageing-associated decline in kidney function.

Unbalanced intakes of sodium and potassium among Tunisian adults: A cross-sectional study

The prevention and management of hypertension are untimely associated with a lowering of sodium intake. The present study aimed to evaluate the sodium and potassium intake levels of Tunisian population through measurement of 24-hr urinary sodium excretions. A randomly, multistage, cross-sectional study was conducted in an urban region (Bizerte) in Tunisia during 2015. The target population involved adults aged from 25 to 64 years. Sodium, potassium, and creatinine concentrations were determined in each urine sample using indirect potentiometric method. From the 420 selected participants, only 194 gave urine samples complying completeness criteria. A multivariate regression model was used to assess the variables related to sodium and potassium excretion. The daily mean excretion of sodium and potassium was 138.3 ± 46.5 mmol/d (corresponding to 8.1 ± 2.7 g/d of salt intake) and 61.0 ± 22.7 mmol/d, respectively. More than 87.1% of the participants (89.8% for men vs. 84.9% for women; p = .31) exceeded the WHO recommendation of 5 g/d. The upper limit of 10 g salt intake per day was still exceeded by 26.3%. After adjusted analysis, sex (for women, coef = -1.6; (95% CI: -2.4, -0.7)), level of instruction (≥30 kg/m2, coef = +1.1; (95% IC: 0.4-2.0)), and body mass index (≥30 kg/m2, coef = +1.1; (95% CI: 0.1, 2.0)) were associated with the sodium excretion. High sodium intake and inadequate potassium intake were found among participants. This consumption profile complies with the diet westernization context occurring in Tunisia. The initiated strategy focused on the downward of sodium in bread (the main source of salt intake) seems to be promising.

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

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.

Spot Urine Samples to Estimate Na and K Intake in Patients With Chronic Kidney Disease and Healthy Adults: A Secondary Analysis From a Controlled Feeding Study

OBJECTIVE

The objective of this study was to assess the agreement between estimated 24-hour urinary sodium excretion (e24hUNa) and estimated 24-hour urinary potassium excretion (e24hUK), calculated from a spot urine sample using several available equations and actual sodium and potassium intake from a controlled diet in both healthy participants and those with chronic kidney disease (CKD).

DESIGN AND METHODS

This study is a secondary analysis of a controlled feeding study in CKD patients matched to healthy controls. Participants (n = 16) consumed the controlled diet, which provided ∼2400 mg Na/day and ∼3000 mg K/day, for 8 days. On days 7 and 8, participants consumed all meals and collected all urine in an inpatient research setting, and they were discharged on day 9. The day 7 morning spot urine sample was used to calculate e24hUNa and e24hUK, which was compared with known sodium and potassium intake, respectively.

RESULTS

Average e24hUNa from the INTERSALT and Tanaka-Na equations were higher than actual sodium intake by 373 mg and 559 mg, respectively, though the differences were not significant. e24hUNa from the Nerbass-SALTED equation in CKD participants was significantly higher than actual sodium intake by ∼2000 mg (P < .001), though e24hUNa from the Nerbass-RRID equation was not different from intake. e24hUK from the Tanaka-K equation was significantly lower than actual potassium intake (P < .001). For both e24hUNa and e24hUK for all participants, agreement with actual intake was poor, and e24hUNa and e24hUK were not correlated with actual sodium or potassium intake, respectively.

CONCLUSION

e24hUNa and e24hUK are poor indicators of true sodium and potassium intake, respectively, in both healthy and CKD participants. Findings should be confirmed in larger sample sizes with varying levels of dietary sodium and potassium.

Estimation of Sodium and Potassium Intake: Current Limitations and Future Perspectives

Globally, average dietary sodium intake is double the recommended amount, whereas potassium is often consumed in suboptimal amounts. High sodium diets are associated with increased cardiovascular and renal disease risk, while potassium may have protective properties. Consequently, patients at risk of cardiovascular and renal disease are urged to follow these recommendations, but dietary adherence is often low due to high sodium and low potassium content in processed foods. Adequate monitoring of intake is essential to guide dietary advice in clinical practice and can be used to investigate the relationship between intake and health outcomes. Daily sodium and potassium intake is often estimated with 24-h sodium and potassium excretion, but long-term balance studies demonstrate that this method lacks accuracy on an individual level. Dietary assessment tools and spot urine collections also exhibit poor performance when estimating individual sodium and potassium intake. Collection of multiple consecutive 24-h urines increases accuracy, but also patient burden. In this narrative review, we discuss current approaches to estimating dietary sodium and potassium intake. Additionally, we explore alternative methods that may improve test accuracy without increasing burden.

Genome-Wide Association Meta-Analysis of Individuals of European Ancestry Identifies Suggestive Loci for Sodium Intake, Potassium Intake, and Their Ratio Measured from 24-Hour or Half-Day Urine Samples

BACKGROUND

Excess sodium intake and insufficient potassium intake are risk factors for hypertension, but there is limited knowledge regarding genetic factors that influence intake. Twenty-hour or half-day urine samples provide robust estimates of sodium and potassium intake, outperforming other measures such as spot urine samples and dietary self-reporting.

OBJECTIVE

The aim of this study was to investigate genomic regions associated with sodium intake, potassium intake, and sodium-to-potassium ratio measured from 24-h or half-day urine samples.

METHODS

Using samples of European ancestry (mean age: 54.2 y; 52.3% women), we conducted a meta-analysis of genome-wide association studies in 4 cohorts with 24-h or half-day urine samples (n = 6,519), followed by gene-based analysis. Suggestive loci (P < 10-6) were examined in additional European (n = 844), African (n = 1,246), and Asian (n = 2,475) ancestry samples.

RESULTS

We found suggestive loci (P < 10-6) for all 3 traits, including 7 for 24-h sodium excretion, 4 for 24-h potassium excretion, and 4 for sodium-to-potassium ratio. The most significant locus was rs77958157 near cocaine- and amphetamine-regulated transcript prepropeptide (CARTPT) , a gene involved in eating behavior and appetite regulation (P = 2.3 × 10-8 with sodium-to-potassium ratio). Two suggestive loci were replicated in additional samples: for sodium excretion, rs12094702 near zinc finger SWIM-type containing 5 (ZSWIM5) was replicated in the Asian ancestry sample reaching Bonferroni-corrected significance (P = 0.007), and for potassium excretion rs34473523 near sodium leak channel (NALCN) was associated at a nominal P value with potassium excretion both in European (P = 0.043) and African (P = 0.043) ancestry cohorts. Gene-based tests identified 1 significant gene for sodium excretion, CDC42 small effector 1 (CDC42SE1), which is associated with blood pressure regulation.

CONCLUSIONS

We identified multiple suggestive loci for sodium and potassium intake near genes associated with eating behavior, nervous system development and function, and blood pressure regulation in individuals of European ancestry. Further research is needed to replicate these findings and to provide insight into the underlying genetic mechanisms by which these genomic regions influence sodium and potassium intake.

Impaired Daytime Urinary Sodium Excretion Impacts Nighttime Blood Pressure and Nocturnal Dipping at Older Ages in the General Population

The circadian rhythm of urinary sodium excretion is related to the diurnal blood pressure regulation (BP) and the nocturnal dipping pattern. The renal sodium excretion expressed as daytime/nighttime ratio impacts BP, but a limited number of studies have investigated this topic to date. In this cross-sectional study, we aimed to investigate the impact of different daily patterns of sodium excretion (comparing low with high ratios) on BP and nocturnal dipping and to explore the relationship with age. Twenty-four-hour ambulatory BP monitoring and daytime and nighttime urinary sodium collections were used to assess 1062 subjects in Switzerland. Analyses were performed according to the day/night urinary sodium excretion ratio quartiles (Q1-Q4) and by age group (≤50 and ≥50 years). Subjects in Q1 can be considered low excretors of sodium during the daytime since the rate of sodium excretion during the daytime was 40% lower than that of subjects in Q4. Quartiles of the day/night urinary sodium excretion ratio showed that subjects in Q1 were 7 years older and had respectively 6 and 5 mmHg higher nighttime systolic and diastolic BP and a higher nocturnal dipping compared with subjects in Q4 (p-value ≤0.001). Associations found were significant only for subjects older than 50 years (all p < 0.05). The present results suggest that a decreased capacity to excrete sodium during daytime is more prevalent as age increases and that it impacts nighttime blood pressure and nocturnal dipping in older subjects.

Formulas developed based on the ratio of urea nitrogen to creatinine concentrations obtained from multiple spot urine samples are acceptable to predict protein intake at group level but not at individual level

In this study, we hypothesized that spot urine can be used to predict protein intake at both group and individual levels. Participants (n = 369) of this study were recruited from all 47 prefectures in Japan. Sex-specific formulas were developed based on the ratio of urea nitrogen to creatinine concentration obtained from 3 spot urine samples. Validity of the formulas was examined against two 24-hour urine collections for 7 combinations of spot urine (single and means of 2 or 3 samples) using t test (mean estimation), Spearman correlation, and Bland-Altman plot (individual bias). Means of measured protein intake based on 24-hour urinary excretions were 87.3 g/d (standard deviation 19.7) for men and 70.5 g/d (standard deviation 14.7) for women. Irrespective of sex, the predicted intakes were not significantly different (within 2.7% of differences) from those measured by urinary excretions. Predicted intakes were moderately correlated with measured intakes (men, 0.45-0.60; women, 0.35-0.53). Even after using the mean of 3 samples, Bland-Altman plots showed a considerably wide limit of agreement (men, -30 to 33 g/d; women, -27 to 24 g/d). Except for using single spot urine samples in women, the formula tended to overestimate intake at a lower and underestimate at a higher level of protein intake (slope: men, -0.47 [P < .0001]; women, -0.38 [P = .002]). In conclusion, predictive formulas developed in this study can be used to predict protein intake at group level or to rank individuals' intake but not to predict absolute intake at individual level.

Estimating 24-h urinary sodium excretion from casual spot urine specimen among hypertensive patients in Northwest China: the Salt Substitute and Stroke Study

OBJECTIVE

To develop an equation that can estimate the 24-h urinary Na excretion by using casual spot urine specimen for older hypertensive participants in rural Ningxia and further to compare with the INTERSALT method, Kawasaki method and Tanaka method.

DESIGN

Older hypertensive participants in rural Ningxia provided their casual spot urine samples and 24-h urine samples between January 2015 and February 2017. Sex-specific equation was developed using linear forward stepwise regression analysis. Model fit was assessed using adjusted R2. Approximately half of all participants were randomly selected to validate the equation. Mean differences, intraclass correlation coefficients and Bland-Altman plots were used to evaluate the performance of all methods.

SETTING

Pingluo County and Qingtongxia County in Ningxia Hui Autonomous Region, China.

PARTICIPANTS

Older hypertensive participants in rural Ningxia.

RESULTS

Totally, 807 of 1120 invited participants provided qualified 24-h urine samples and spot urine samples. There was no statistical difference comparing the laboratory-based method against the new method and the INTERSALT method, while Kawasaki method had the largest bias with a mean difference of 40·81 g/d (95 % CI 39·27, 42·35 g/d). Bland-Altman plots showed similar pattern of the results.

CONCLUSION

The INTERSALT method and the new equation have the potential to estimate the 24-h urinary Na excretion in this study population. However, the extrapolation of the results to other population needs to be careful. Future research is required to establish a more reliable method to estimate 24-h urinary Na excretion.

A New Approach Is Needed to Evaluate 24-Hour Urinary Sodium Excretion Using Spot Urines: A Validation Study in a Chinese Child Population

Background

Accurate assessments of sodium intake in children are important for the early prevention of cardiovascular disease. There is currently no accurate simple and feasible sodium intake approach for children. This study intends to validate the accuracy of 24‐hour urinary sodium excretion (UNaV) estimation in children using 3 common formulas: the Kawasaki, INTERSALT (International Cooperative Study on Salt, Other Factors, and Blood Pressure), and Tanaka formulas.

Methods and Results

A hospital‐based child population in China was enrolled in the study and completed 24‐hour urine sample collection. Concentrations of sodium, potassium, and creatinine in 24‐hour urine and spot urine samples were measured. Mean difference as well as absolute and relative differences and misclassification between estimation and measurement of UNaV with 3 commonly used formulas were compared and analyzed. A total of 129 participants aged 5 to 16 years were eligible for analysis. Mean measured UNaV was 2694.9 mg/day. Mean differences between estimated and measured UNaV by the Kawasaki, INTERSALT, and Tanaka formulas were 2367.6, 26.4, and 258.8 mg/day, respectively. Proportions of relative differences of over 40% for the Kawasaki, INTERSALT, and Tanaka formulas were 79.8%, 34.9%, and 38.5%, respectively. Misclassification rates were 73.1% for Kawasaki, 69.0% for INTERSALT, and 62.4% for Tanaka at the individual level.

Conclusions

The results from our study do not support estimation of UNaV for children by the Kawasaki, INTERSALT, and Tanaka formulas using single spot urine samples because of the potential risk for misclassification at the individual level.