Estimating the urinary sodium excretion in patients with chronic kidney disease is not useful in monitoring the effects of a low-salt diet

Dietary evaluation of sodium intake in patients with chronic kidney disease

Introduction

Introduction: high sodium intake is a risk factor for diseases such as systemic arterial hypertension, stroke, left ventricular hypertrophy, and chronic kidney disease (CKD). Objective: to evaluate the correlation between estimated sodium intake by dietary intake and 24-hour urinary excretion in patients with non-dialysis CKD. Material and Methods: a cross-sectional study with 151 individuals. Demographic, socioeconomic, clinical and lifestyle data were evaluated. Sodium was dosed in 24-hour urine and estimated by 24-hour Food Recall (R24h). To evaluate the association between demographic, anthropometric, nutritional and laboratory variables with sodium excretion in 24-hour urine, variance analysis (ANOVA) or Kruskal-Wallis test were used. The correlation between 24-hour urinary sodium excretion and dietary sodium intake was performed by Spearman's correlation coefficient. Results: mean age was 60.8 ± 11.8 years, 51.7 % were women. Hypertensive patients, 88.9 %; diabetics, 45.0 %; and 39.1 % were in stage 3B of CKD. Median sodium excretion in 24-hour urine was 112.2 mmol/L and R24h intake was 833.8 mg/day. Individuals belonging to the highest tertile of sodium excretion (T3) presented lower PTH values, and those with lower tertile (T1), higher serum HDL-c levels (p < 0.05). There was no statistical correlation between dietary sodium intake and 24-hour urine excretion (p-value = 0.241). Conclusion: the non-correlation between sodium obtained by 24-hour urinary excretion and dietary intake demonstrates the fragility of the estimation of sodium excretion through the dietary survey.

Total Body Sodium Balance in Chronic Kidney Disease

Excess sodium intake is a leading but modifiable risk factor for mortality, with implications on hypertension, inflammation, cardiovascular disease, and chronic kidney disease (CKD). This review will focus mainly on the limitations of current measurement methods of sodium balance particularly in patients with CKD who have complex sodium physiology. The suboptimal accuracy of sodium intake and excretion measurement is seemingly more marked with the evolving understanding of tissue (skin and muscle) sodium. Tissue sodium represents an extrarenal influence on sodium homeostasis with demonstrated clinical associations of hypertension and inflammation. Measurement of tissue sodium has been largely unexplored in patients with CKD. Development and adoption of more comprehensive and dynamic assessment of body sodium balance is needed to better understand sodium physiology in the human body and explore therapeutic strategies to improve the clinical outcomes in the CKD population.

A Method for Estimating 24-Hour Urinary Sodium Excretion by Casual Urine Specimen in Chinese Hypertensive Patients

BACKGROUND

High salt intake is a known risk factor of hypertension, which in turn increases the risk of stroke and cardiovascular diseases. The aim of this study was to develop and evaluate a method for predicting 24-hour urinary sodium excretion (UNa24h) using casual urine specimens in Chinese hypertensive patients.

METHODS

A total of 966 patients with hypertension were included from 8 provinces across China. A UNa24h prediction model (Sun_C method) was developed for males and females using linear regression based on age, weight, sodium concentration in the spot urine (UNaspot), and creatinine concentration in the spot urine (UCrspot). The data were split into the training (70%) and testing (30%) sets to, respectively, develop and evaluate the Sun_C method.

RESULTS

Compared with the Kawasaki, INTERSALT, and Tanaka methods, Sun_C method achieved a low and consistent mean bias (1.1 mmol/d) within the range from 106 to 212 mmol/d of UNa24h (equivalent to NaCl intake of 6-12 g/d). In addition, the Sun_C method showed no significant difference between the measured and estimated UNa24h in a paired t-test (P = 0.689). At individual level, Sun_C method had 79.8% of individuals at the cutoff under ±30% level.

CONCLUSIONS

Sun_C method may prove a reasonable method to estimate the daily dietary sodium intakes (particularly in the range of 6-12 g/d of NaCl) in Chinese hypertensive patients using spot urine measurements. As the amount of data increases in the future, the performance of our formulae will be further improved.

At-home determination of 24-h urine sodium excretion: Validation of chloride test strips and multiple spot samples

Sodium intake and compliance with dietary sodium modification are typically assessed using a 24-h urine collection analyzed using flame photometry, but this is inconvenient. Spot urine samples have been investigated as alternatives to 24-h collections, but their accuracy is poor. Since sodium and chloride are present in equal concentrations in dietary salt, chloride test strips may provide a suitable proxy for at-home measurement of urine sodium concentrations. We aimed to determine whether (i) chloride test strips provide a reliable measure of urinary sodium compared to the gold standard flame photometry and (ii) multiple spot samples accurately reflect 24-h urine sodium. We recruited 43 participants (19 males) aged 23.6 ± 0.6 years to complete multiple consecutive spot samples (morning and evening) along with a 24-h urine sodium collection. Urine 24-h sodium estimates using chloride test strips (114.6 ± 7.5 mmol/day) were highly correlated (r = 0.900, p < 0.0001) with flame photometry (121.1 ± 7.7 mmol/day) with a bias of -6.53 ± 22.2 mmol/day. Use of a three-spot sample average (both morning and evening spot samples) with a correction factor applied (122.9 ± 4.1 mmol/day) provided a good approximation of 24-h sodium measured by flame photometry (125.6 ± 9.0 mmol/day), with a bias of -2.55 ± 43.9 mmol/day. Chloride test strips applied to a 24-h urine collection provide a highly accurate measure of urinary sodium excretion, permitting convenient at-home sample collection and analysis. Their application to multiple spot samples provides a reasonable approximation of sodium excretion that can be used to conveniently monitor attempts at dietary sodium manipulation, without the inconvenience of completing a 24-h urine sample.

Change in mean salt intake over time using 24-h urine versus overnight and spot urine samples: a systematic review and meta-analysis

Background

Little is known about the capacity of overnight and spot urine samples to estimate changes in mean salt intake over time. The objective of this review was to compare the estimates of change in mean population salt intake based on 24-h urine and overnight/spot urine samples.

Methods

Studies were systematically identified through searches of peer-reviewed databases (Medline, Embase, Global Health, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews) and grey literature. Studies that reported estimates of mean salt intake for at least two time points based on both 24-h and overnight/spot urines were deemed eligible. The capacity of overnight/spot urine samples to estimate the change in mean salt intake was assessed both at the individual-study level and overall through random-effects meta-analyses. The level of heterogeneity was assessed through the I² statistic. Subgroup and sensitivity analyses were conducted to explore possible sources of heterogeneity, and check the robustness of the findings from the primary analysis.

Results

A total of 1244 records were identified, 50 were assessed as full text, and 14 studies met the criteria, capturing data on 7291 participants from seven countries. Nine and five studies collected overnight and spot urines, respectively. The comparison of the change in mean salt intake between 24-h and overnight/spot urines showed some inconsistencies at the individual study-level. The pooled mean change in salt intake was − 0.43 g/day (95% CI − 1.16 to 0.30; I² = 95%) using 24-h urines, and − 0.22 g/day (− 0.65 to 0.20; I² = 87%) using overnight/spot urines, with a pooled difference-in-differences between the two methods of 0.27 g/day (− 0.23 to 0.77; I² = 89%). Subgroup analyses showed substantial heterogeneity for most subgroups. Sensitivity analyses did not change the effect observed in the primary analysis.

Conclusion

The evidence for the capacity of overnight/spot urines to estimate changes in mean salt intake over time is uncertain. More research where overnight/spot urines are collected in parallel with 24-h urines is needed to enable a more in-depth evaluation of these alternative approaches to estimating change in mean salt intake.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-020-00651-8.

Nutritional management in patients with chronic kidney disease

The global prevalence of chronic kidney disease (CKD) is increasing with the aging of populations worldwide. As kidney function declines, the accumulation of metabolic waste products and excessive electrolytes can significantly impair the health of patients with CKD. As nutritional management of patients with CKD is thought to control uremic symptoms and provide beneficial effects on the progression of kidney dysfunction, the diet of patients with CKD should be an important consideration in their care. Many guidelines recommend limiting protein intake in these patients, as high-protein diets aggravate kidney dysfunction. Excess sodium may be associated with CKD progression and all-cause mortality and, therefore, limiting salt intake is generally recommended. Low potassium is associated with muscle weakness and hypertension, whereas high potassium is associated with cardiac arrhythmia. Therefore, recent guidelines recommend adjusting dietary potassium intake on an individual basis to maintain serum potassium levels within the normal range. Appropriate dietary calcium intake is recommended to maintain calcium balance in patients with CKD G3, G4. Given the many dietary considerations for patients with CKD, effective nutritional management is challenging. Individualized strategies are needed to ensure the best outcome for patients with CKD.