Estimation of 24-h urinary sodium excretion using lean body mass and overnight urine collected by a pipe-sampling method

Sodium Management in Kidney Disease: Old Stories, New Tricks

Excessive dietary sodium intake is associated with an increased risk of hypertension, especially in the setting of chronic kidney disease (CKD). Although implementation of a low-sodium diet in patients with CKD generally is recommended, data supporting the efficacy of this practice is mostly opinion-based. Few controlled studies have investigated the specific association of dietary sodium intake and cardiovascular events and mortality in CKD. Furthermore, in epidemiologic studies, the association of sodium intake with CKD progression, cardiovascular risk, and mortality is not homogeneous, and both low- and high-sodium intake has been associated with adverse health outcomes in different studies. In general, the adverse effects of high dietary sodium intake are more apparent in the setting of advanced CKD. However, there is no established definitive target level of dietary sodium intake in different CKD stages based on glomerular filtration rate and albuminuria/proteinuria. This review discusses the current challenges regarding the rationale of sodium restriction, target levels and assessment of sodium intake, and interventions for sodium restrictions in CKD in relation to clinical outcomes.

Interventions That Successfully Reduced Adults Salt Intake-A Systematic Review

Background: Adequate sodium intake is important for lowering blood pressure and thus reducing cardiovascular disease risk and other complications. The aim of this review is to identify recent interventions around the world that have been successful in reducing salt intake. Methods: A search in the PubMed, Web of Science and Scopus databases was performed. We include studies published in the last 10 years; randomized trials, pilot intervention without a control arm or experimental study; adult participants; and interventions that successfully reduced salt intake. Study quality was assessed. Results: We included 21 studies, 16 randomized intervention trials and five nonrandomized intervention studies. Eleven interventions described health and nutritional education, seven interventions described nutritional education plus other interventions, and three studies used salt meters to reduce sodium intake. Conclusion: Health and nutritional education, nutritional education plus other interventions and estimates of salt intake showed success in the reduction of salt consumption. There is no evidence that one type of intervention analyzed is more effective than other in reducing salt consumption, so we must analyze each in which individuals or subpopulations will have the intervention performed and use the most suitable approaches to lead to better results.

Measuring sodium intake: research and clinical applications

Although most current guidelines recommend a daily sodium intake of less than 2.3 g/day, most people do not have a reliable estimate of their usual sodium intake. In this review, we describe the different methods used to estimate sodium intake and discuss each method in the context of specific clinical or research questions. We suggest the following classification for sodium measurement methods: preingestion measurement (controlled intake), peri-ingestion measurement (concurrent), and postingestion measurement. On the basis of the characteristics of the available tools, we suggest that: validated 24-h recall methods are a reasonable approach to estimate sodium intake in large epidemiologic studies and individual clinical counselling sessions, methods (such as single 24-h urine collection, single-time urine collection, or 24-h recall methods), are of value in population-level estimation of mean sodium intake, but are less suited for individual level estimation and a feeding-trial design using a controlled diet is the most valid and reliable method for establishing the effect of reducing sodium to a specific intake target in early phase clinical trials. By considering the various approaches to sodium measurement, investigators and public health practitioners may be better informed in assessing the health implications of sodium consumption at the individual and population level.

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.

Development of objective indicators for quantitative analysis of sodium intake: the sodium to potassium ratio of second-void urine is correlated with 24-hour urinary sodium excretion

BACKGROUND/OBJECTIVES

To date, sodium intake has been evaluated based on spot urine instead of 24-hour (hr) urine collection. Nevertheless, the optimal method for assessing daily sodium intake remains unclear.

SUBJECTS/METHODS

Fifteen male (age 32.7 ± 6.5 years) participants were offered 3 meals with a total of 9-10 g salt over 24 hours, and 24-hr urine was collected from the second-void urine of the first day to the first-void urine of the second day. Twenty-four-hr urinary sodium (24UNa) was estimated using Tanaka's equation and the Korean formula, and spot urine Na, potassium (K), chloride (Cl), urea nitrogen (UN), creatinine (Cr), specific gravity (SG) and osmolality (Osm) were measured. The ratios of urinary Na to other parameters were calculated, and correlations with total measured 24UNa were identified.

RESULTS

Average 24-hr urine volume was 1,403 ± 475 mL, and measured 24UNa was 143.9 ± 42.1 mEq (range, 87.1-239.4 mEq). Measured 24UNa was significantly correlated with urinary Na/UN (r = 0.560, P < 0.01), urinary Na/Osm (r = 0.510, P < 0.01), urinary Na/Cr (r = 0.392, P < 0.01), urinary Na/K (r = 0.290, P < 0.01), 24UNa estimated using Tanaka's equation (r = 0.452, P < 0.01) and the Korean formula (r = 0.414, P < 0.01), age (r = 0.548, P < 0.01), weight (r = 0.497, P < 0.01), and height (r = 0.393, P < 0.01) in all spot urine samples. Estimated 24UNa based on the second-void spot urine of the first day tended to be more closely correlated with measured 24UNa than were estimates from the other spot urine samples. The significant parameters correlated with the second-void urine of the first day were urinary Na/K (r = 0.647, P < 0.01), urinary Na/Cr (r = 0.558, P < 0.05), and estimated 24UNa using Tanaka's equation (r = 0.616, P < 0.05) and the Korean formula (r = 0.588, P < 0.05).

CONCLUSIONS

Second-void urine is more reliable than first-void urine for estimating 24UNa. Urinary Na/K in the second-void urine on the first day is significantly correlated with 24UNa. Further studies are needed to establish the most reliable index and the optimal time of urine sampling for predicting 24UNa.

Close association between circulating high-sensitivity cardiac troponin I and metabolic syndrome in the general population

Individuals with metabolic syndrome reportedly have an increased risk of cardiovascular disease, although the association between asymptomatic myocardial damage and metabolic syndrome has not been sufficiently investigated. The present study investigated possible associations between circulating cardiac troponin and metabolic syndrome or related factors. Subjects undergoing their annual health checkups were enrolled in the study (n = 1242). Laboratory measurements included serum high-sensitivity cardiac troponin I (hs-cTnI) and plasma B-type natriuretic peptide (BNP). Individual salt intake was estimated by calculating 24-h urinary sodium excretion from spot urine. Subjects whose electrocardiograms revealed ST-T segment abnormalities or who had renal insufficiency or a history of cardiovascular events were excluded. Subjects with metabolic syndrome had higher hs-cTnI levels than those without, but their BNP levels were equivalent. hs-cTnI levels were significantly associated with the presence and components of metabolic syndrome. Logistic regression analysis with the endpoint of hs-cTnI levels higher than the median value identified metabolic syndrome as an independent determinant of increased hs-cTnI levels. Additionally, urinary salt excretion levels were increased in subjects with metabolic syndrome or any of its components. Logistic regression analysis with the endpoint of metabolic syndrome revealed that hs-cTnI levels were independently associated with the presence of metabolic syndrome. A close association between hs-cTnI levels and the presence of metabolic syndrome, at least partially mediated by increased salt intake, was confirmed to exist in the general population. The findings support the idea that patients with metabolic syndrome develop asymptomatic myocardial damage without obvious ischaemic findings, which leads to increased cardiovascular risk.

[Measurement of dietary sodium intake in a group of children from one to 18 months of age in a pediatric service in Cali, Colombia]

INTRODUCTION

The fatty streaks in an arterial wall can appear from the third year of age, and they show an association with atherogenic risk factors such as hypertension and sodium in the diet. Given the difficulty of data gathering, few studies report the intake of sodium in the diet.

OBJECTIVE

To determine average sodium intake in the diet of children between one and 18 months of age through a three-day dietary survey.

MATERIALS AND METHODS

This was a cross-sectional study with 48 children without renal disease or diet restrictions seen in pediatric practice between January and June, 2011. It included a dietary survey for the parents, nutritional status classification by anthropometry, and blood pressure measurements. Sodium content and other nutrients in the diet program were analyzed with the International Food Consumption Program (CERES), anthropometry with the World Health Organization Anthro program, and Epi-info for socio-demographic characteristics.

RESULTS

In total, 69% of children had high sodium consumption, 6.2% had high blood pressure, and 20.7% were overweight and obese.

CONCLUSIONS

The prevalence of hypertension exceeds that reported for Colombia (1-3%). Two of the three children with high blood pressure had high sodium intake and they were overweight and obese, with values above those reported for Colombian children (16%). We suggest to measure blood pressure early, and to restrict salt and sugar in food for infants and children under two years of age. Also, larger studies should be conducted to collect population data on sodium intake and develop appropriate and timely intervention strategies to reduce risks in adulthood.

Reliable Quantification of the Potential for Equations Based on Spot Urine Samples to Estimate Population Salt Intake: Protocol for a Systematic Review and Meta-Analysis

Background

Methods based on spot urine samples (a single sample at one time-point) have been identified as a possible alternative approach to 24-hour urine samples for determining mean population salt intake.

Objective

The aim of this study is to identify a reliable method for estimating mean population salt intake from spot urine samples. This will be done by comparing the performance of existing equations against one other and against estimates derived from 24-hour urine samples. The effects of factors such as ethnicity, sex, age, body mass index, antihypertensive drug use, health status, and timing of spot urine collection will be explored. The capacity of spot urine samples to measure change in salt intake over time will also be determined. Finally, we aim to develop a novel equation (or equations) that performs better than existing equations to estimate mean population salt intake.

Methods

A systematic review and meta-analysis of individual participant data will be conducted. A search has been conducted to identify human studies that report salt (or sodium) excretion based upon 24-hour urine samples and spot urine samples. There were no restrictions on language, study sample size, or characteristics of the study population. MEDLINE via OvidSP (1946-present), Premedline via OvidSP, EMBASE, Global Health via OvidSP (1910-present), and the Cochrane Library were searched, and two reviewers identified eligible studies. The authors of these studies will be invited to contribute data according to a standard format. Individual participant records will be compiled and a series of analyses will be completed to: (1) compare existing equations for estimating 24-hour salt intake from spot urine samples with 24-hour urine samples, and assess the degree of bias according to key demographic and clinical characteristics; (2) assess the reliability of using spot urine samples to measure population changes in salt intake overtime; and (3) develop a novel equation that performs better than existing equations to estimate mean population salt intake.

Results

The search strategy identified 538 records; 100 records were obtained for review in full text and 73 have been confirmed as eligible. In addition, 68 abstracts were identified, some of which may contain data eligible for inclusion. Individual participant data will be requested from the authors of eligible studies.

Conclusions

Many equations for estimating salt intake from spot urine samples have been developed and validated, although most have been studied in very specific settings. This meta-analysis of individual participant data will enable a much broader understanding of the capacity for spot urine samples to estimate population salt intake.

Evaluation of Equations for Predicting 24-Hour Urinary Sodium Excretion from Casual Urine Samples in Asian Adults

BACKGROUND

The collection of 24-h urine samples for the estimation of sodium intake is burdensome, and the utility of spot urine samples in Southeast Asian populations is unclear.

OBJECTIVE

We aimed to assess the validity of prediction equations with the use of spot urine concentrations.

METHODS

A sample of 144 Singapore residents of Chinese, Malay, and Indian ethnicity aged 18-79 y were recruited from the Singapore Health 2 Study conducted in 2014. Participants collected urine for 24 h in multiple small bottles on a single day. To determine the optimal collection time for a spot urine sample, a 1-mL sample was taken from a random bottle collected in the morning, afternoon, and evening. Published equations and a newly derived equation were used to predict 24-h sodium excretion from spot urine samples.

RESULTS

The mean ± SD concentration of sodium from the 24-h urine sample was 125 ± 53.4 mmol/d, which is equivalent to 7.2 ± 3.1 g salt. Bland-Altman plots showed good agreement at the group level between estimated and actual 24-h sodium excretion, with biases for the morning period of -3.5 mmol (95% CI: -14.8, 7.8 mmol; new equation) and 1.46 mmol (95% CI: -10.0, 13.0 mmol; Intersalt equation). A larger bias of 25.7 mmol (95% CI: 12.2, 39.3 mmol) was observed for the Tanaka equation in the morning period. The prediction accuracy did not differ significantly for spot urine samples collected at different times of the day or at a random time of day (P = 0.11-0.76).

CONCLUSION

This study suggests that the application of both our own newly derived equation and the Intersalt equation to spot urine concentrations may be useful in predicting group means for 24-h sodium excretion in urban Asian populations.

Dietary Sodium Consumption Predicts Future Blood Pressure and Incident Hypertension in the Japanese Normotensive General Population

BACKGROUND

Although there is a close relationship between dietary sodium and hypertension, the concept that persons with relatively high dietary sodium are at increased risk of developing hypertension compared with those with relatively low dietary sodium has not been studied intensively in a cohort.

METHODS AND RESULTS

We conducted an observational study to investigate whether dietary sodium intake predicts future blood pressure and the onset of hypertension in the general population. Individual sodium intake was estimated by calculating 24-hour urinary sodium excretion from spot urine in 4523 normotensive participants who visited our hospital for a health checkup. After a baseline examination, they were followed for a median of 1143 days, with the end point being development of hypertension. During the follow-up period, hypertension developed in 1027 participants (22.7%). The risk of developing hypertension was higher in those with higher rather than lower sodium intake (hazard ratio 1.25, 95% CI 1.04 to 1.50). In multivariate Cox proportional hazards regression analysis, baseline sodium intake and the yearly change in sodium intake during the follow-up period (as continuous variables) correlated with the incidence of hypertension. Furthermore, both the yearly increase in sodium intake and baseline sodium intake showed significant correlations with the yearly increase in systolic blood pressure in multivariate regression analysis after adjustment for possible risk factors.

CONCLUSIONS

Both relatively high levels of dietary sodium intake and gradual increases in dietary sodium are associated with future increases in blood pressure and the incidence of hypertension in the Japanese general population.

Methodological issues in estimating sodium intake in the Korea National Health and Nutrition Examination Survey

For policy goal setting, efficacy evaluations, and the development of related programs for reducing sodium intake, it is essential to accurately identify the amount of sodium intake in South Korea and constantly monitor its trends. The present study aimed to identify the status of sodium intake in South Korea and to review the methods and their validity for estimating sodium intake in each country; through this, we aim to determine more accurate methods for determining sodium intake and to monitor the trend in sodium intake for Korean citizens in the future. Using 24-hour dietary recall data from the 2012 Korea National Health and Nutrition Examination Survey (KNHANES) to estimate daily sodium intake, the average daily sodium intake among Koreans was 4,546 mg (men, 5,212 mg; women, 3,868 mg). In addition to the nutrition survey that uses the 24-hour dietary recall method, sodium intake can also be calculated from the amount of sodium excreted in 24-hour urine, 8-hour overnight urine, and spot urine samples. Although KNHANES uses the 24-hour dietary recall method to estimate the sodium intake, the 24-hour dietary recall method has the disadvantage of not being able to accurately determine the amount of sodium intake owing to its unique characteristics of the research method and in the processing of data. Although measuring the amount of sodium excreted in 24-hour urine is known to be the most accurate method, because collecting 24-hour urine from the general population is difficult, using spot urine samples to estimate sodium intake has been suggested to be useful for examining the trend of sodium intake in the general population. Therefore, we planned to conduct a study for estimating of 24-hour sodium excretion from spot urine and 8-hour overnight urine samples and testing the validity among subsamples in the KNHANES. Based on this result, we will adopt the most appropriate urine collection method for estimating population sodium intake in South Korea.

Not salt taste perception but self-reported salt eating habit predicts actual salt intake

Excessive dietary salt intake is related to cardiovascular morbidity and mortality. Although dietary salt restriction is essential, it is difficult to achieve because of salt palatability. However, the association between salt perception or salt eating habit and actual salt intake remains uncertain. In this study, we recruited 74 healthy young individuals. We investigated their salt-eating habits by questionnaire and salt taste threshold through a rating scale that used serial dilution of a sodium chloride solution. Predicted 24-hr urinary salt excretions using Kawasaki's and Tanaka's equations estimated dietary salt intake. Participants' mean age was 35 yr, and 59.5% were male. Salt sense threshold did not show any relationship with actual salt intake and a salt-eating habit. However, those eating "salty" foods showed higher blood pressure (P for trend=0.048) and higher body mass index (BMI; P for trend=0.043). Moreover, a salty eating habit was a significant predictor for actual salt intake (regression coefficient [β] for Kawasaki's equation 1.35, 95% confidence interval [CI] 10-2.69, P=0.048; β for Tanaka's equation 0.66, 95% CI 0.01-1.31, P=0.047). In conclusion, a self-reported salt-eating habit, not salt taste threshold predicts actual salt intake.

The prevalence and characteristics of microalbuminuria in the general population: a cross-sectional study

Background

Microalbuminuria is a marker of cardiovascular events. This study investigated the prevalence of microalbuminuria in the general population and the factors that can affect urinary excretion of albumin.

Methods

Apparently healthy subjects who participated in a health checkup at our hospital were enrolled in this study (n = 7963, male 64.0%, 56.2 ± 11.8 years old) Urine samples were collected for the measurement of albumin concentrations, which were expressed as the ratio of urinary albumin to creatinine concentrations (UACR [mg/g Cr]). Individual salt intake was assessed by estimating the 24-hour urinary salt excretion of subjects.

Results

The mean blood pressure was 124 ± 15/76 ± 10 mmHg and 31.6%, 7.4%, and 44.1% of subjects had hypertension, diabetes mellitus, and dyslipidemia, respectively. Urinary albumin was detected in 7265 subjects (91.2%: UACR ≥ 300 mg/g Cr, 0.5%; 300 > UACR ≥ 30 mg/g Cr, 4.6%; 30 > UACR ≥ 20 mg/g Cr, 2.4%; 20 > UACR ≥ 10 mg/g Cr, 8.7%; 10 > UACR ≥ 5 mg/g Cr, 21.8%; UACR < 5 mg/g Cr, 53.2%). In subjects with detectable albuminuria, UACR was independently correlated with age, systolic blood pressure, serum creatinine, fasting plasma glucose, and salt intake after adjustment for possible factors (P < 0.0001).

Conclusion

The prevalence of microalbuminuria was found to be 4.6% in the general population. The urinary excretion of albumin was closely associated with blood pressure and salt intake. These data indicated the importance of salt restriction for the prevention of cardiovascular disease and end-stage renal disease.

Significance of estimated salt excretion as a possible predictor of the efficacy of concomitant angiotensin receptor blocker (ARB) and low-dose thiazide in patients with ARB resistance

The purpose of this study was to assess the factors affecting the efficacy of combination therapy with losartan and thiazide, with a focus on the significance of salt excretion, via a multicenter observational study. Adult patients with essential hypertension showing therapy resistance to angiotensin receptor blocker (ARB) as a monotherapy or in combination with Ca channel blockers (CCB) were enrolled, and their previously administered ARBs were replaced with the combination tablet containing losartan (50 mg per day) and hydrochlorothiazide (12.5 mg per day). Blood pressure and biochemical parameters were monitored for a year. The baseline blood pressure (153.4±14.8/86.4±11.3 mm Hg) was significantly lowered at the 3rd month (137.3±17.4/78.2±11.1 mm Hg, n=93) and was maintained at this lower level until the 12th month (135.3±14.0/76.4±11.1 mm Hg, n=74). The baseline value of estimated salt excretion (eSE), calculated using Tanaka's formula, differed significantly between the high and low treatment response groups, which were defined by the average change in mean blood pressure (MBP-C, -11.3 mm Hg; eSE=10.8±2.9 g per day in high responders vs. 9.2±2.3 g per day in low responders, P=0.004). Univariate and multivariate analyses showed a significant correlation between eSE and MBP-C (R=-0.288, P=0.007) and indicated the clinical effectiveness of eSE as a possible predictor for MBP-C (P=0.021). In addition, the urine Na-to-Cr ratio (NCR) demonstrated significant correlations with eSE (R=0.848, P<0.001) and MBP-C (R=-0.344, P<0.001). These results suggest that eSE or NCR could, to a certain extent, predict the efficacy of combination therapy with losartan and low-dose thiazide in patients demonstrating ARB resistance. Combination therapy with losartan and thiazide might thus be suitable for patients with a large amount of salt excretion.

Estimation of salt intake from spot urine samples in patients with chronic kidney disease

BACKGROUND

High salt intake in patients with chronic kidney disease (CKD) may cause high blood pressure and increased albuminuria. Although, the estimation of salt intake is essential, there are no easy methods to estimate real salt intake.

METHODS

Salt intake was assessed by determining urinary sodium excretion from the collected urine samples. Estimation of salt intake by spot urine was calculated by Tanaka's formula. The correlation between estimated and measured sodium excretion was evaluated by Pearson´s correlation coefficients. Performance of equation was estimated by median bias, interquartile range (IQR), proportion of estimates within 30% deviation of measured sodium excretion (P30) and root mean square error (RMSE).The sensitivity and specificity of estimated against measured sodium excretion were separately assessed by receiver-operating characteristic (ROC) curves.

RESULTS

A total of 334 urine samples from 96 patients were examined. Mean age was 58 ± 16 years, and estimated glomerular filtration rate (eGFR) was 53 ± 27 mL/min. Among these patients, 35 had CKD stage 1 or 2, 39 had stage 3, and 22 had stage 4 or 5. Estimated sodium excretion significantly correlated with measured sodium excretion (R = 0.52, P < 0.01). There was apparent correlation in patients with eGFR <30 mL/min (R = 0.60, P < 0.01). Moreover, IQR was lower and P30 was higher in patients with eGFR < 30 mL/min. Estimated sodium excretion had high accuracy to predict measured sodium excretion, especially when the cut-off point was >170 mEq/day (AUC 0.835).

CONCLUSIONS

The present study demonstrated that spot urine can be used to estimate sodium excretion, especially in patients with low eGFR.

Effect of salt reduction intervention program using an electronic salt sensor and cellular phone on blood pressure among hypertensive workers

We investigated the effectiveness of a workplace intervention program that utilized self-monitoring of daily salt excretion by an electronic salt sensor and sent personalized e-mail advice via cellular phone. Forty-one hypertensive male workers were assigned to intervention and control groups, then counseled together. Intervention group members were asked to measure daily salt excretion and received e-mail advice. After 4 weeks, a greater decrease of blood pressure (BP) was observed in the intervention group, with significant reductions to daily salt excretion and home BP. The new intervention program is considered useful for BP control among hypertensive workers.

Factors associated with brachial-ankle pulse wave velocity in the general population

The present study investigated factors that modify or affect arterial stiffness as assessed by brachial-ankle pulse wave velocity (baPWV) in the general population. Subjects had previously participated in a physical checkup program (n=911), and baPWV and urinary albumin and sodium excretion were also measured. Urine albumin was expressed as the ratio of urine albumin to urine creatinine. Individual salt intake was assessed by estimating 24-h urinary salt excretion and expressed as the ratio of estimated salt intake to body weight. The mean blood pressure and baPWV were 127.1±15.2/77.0±9.5 mm Hg and 15.9±3.3 m s(-1), respectively. Univariate analysis demonstrated that baPWV correlated with various factors including age, blood pressure, electrocardiogram voltage (SV(1)+RV(5)), urine albumin and salt intake. Multivariate regression analysis revealed that electrocardiogram voltage (P<0.001), systolic blood pressure (P<0.0001), urine albumin (P<0.001) and salt intake (P<0.001), independently correlated with baPWV after adjustment for other possible factors. Similar results were obtained for participants not taking any medication. These results suggest that the baPWV value is independently associated with individual salt intake and cardiac and renal damage, and could be a useful procedure for identifying individuals with concealed risk of cardiovascular disease.

A model to predict 24-h urinary creatinine using repeated measurements in an occupational cohort study

Creatinine measurements can be used to standardize urinary pesticide concentrations and to estimate "completeness" of urine collections. Published statistical models exist to predict 24-h creatinine, but many were developed assuming independence among observations. Using correlated repeated measurement data collected from an occupational cohort, the objectives were to create a predictive model for 24-h urinary creatinine and to compare the predictive capability of this model to earlier published models. Using a mixed-model methodology, the appropriate covariance structure was identified and utilized to model the measurements. A backwards elimination model building technique applied to the model building data set (110 adult male subjects and 457 creatinine values) yielded a final model that included variables for body mass index (BMI), height, diabetes, allergies, medical conditions that affect kidney function, use of creatine supplements, and anti-inflammatory medications. Using an external model validation data set (21 adult male subjects' creatinine values, n=91 observations from a total of 275) the predictive performance of the model was evaluated using the mean square prediction error (MSPR) and the Pearson's correlation coefficient (r); its performance was better (MSPR=279184, r=0.43) than any of the earlier models investigated (MSPR: range 658860-393139; r, range 0.18-0.38). In conclusion, the use of a covariance structure that allowed repeated measurements for any one individual to be correlated, improved the predictive performance. For purposes of incomplete urine sample identification in observational studies, it is necessary to collect information in addition to age, gender, and BMI, which are typically used in these settings.

Estimation of 24-hour sodium excretion from spot urine samples

Despite the effects of sodium intake on blood pressure and on response to antihypertensive medication, sodium intake is rarely monitored in clinical practice. The current method, the 24-hour urine collection for sodium excretion, is cumbersome, often incorrectly performed, and not commonly ordered. Further, its results have limited meaning because of the substantial day-to-day variation in sodium intake. A spot urine test to enable convenient, inexpensive, and serial monitoring of sodium excretion would be desirable. In this study, the accuracy of predicting 24-hour sodium excretion from a spot urine sample was assessed. The urine sodium/creatinine ratio was determined from the following urine samples: an "AM sample," submitted at the beginning of the 24-hour urine collection; a "PM sample" collected in the later afternoon/early evening before dinner, at roughly the midpoint of the collection; and a "random sample," collected after its completion. The ratio was then corrected for 24-hour creatinine excretion. The strongest correlation between predicted and actual 24-hour sodium excretion was observed with the PM sample collected near the midpoint (r=0.86, P<.001). This sample also identified persons with sodium excretion <100 mEq/d with a sensitivity of 100% and specificity of 82%. The sodium/creatinine ratio from a spot urine sample collected in the late afternoon/early evening at roughly the midpoint of the 24-hour collection, and adjusted for 24-hour creatinine excretion, strongly correlated with 24-hour sodium excretion. Additional studies are merited to further evaluate the role of the spot urine sample in assessing sodium intake.

Estimation of 24-h sodium excretion from a spot urine sample using chloride and creatinine dipsticks

BACKGROUND

Despite its clinical relevance, sodium intake is seldom monitored by physicians, largely because of shortcomings of the 24-h urine collection for sodium excretion. In a prior study, sodium excretion was shown to be accurately estimated from a late afternoon/early evening spot urine sodium/creatinine ratio, adjusted for 24-h creatinine excretion. In this study, we assessed a more convenient and inexpensive method, using chloride and creatinine dipsticks.

METHODS

Subjects submitted 24-h urine collections along with an "AM sample," collected at the beginning, a "PM sample" collected in the late afternoon/early evening before dinner, at roughly the midpoint, and a "random sample," collected after completion, of the 24-h collection. Predicted 24-h sodium excretion was then determined from the spot urine dipstick chloride/creatinine ratio, measured by two independent observers, and from the spot urine laboratory sodium/creatinine ratio. Both ratios were adjusted for 24-h creatinine excretion.

RESULTS

For PM samples, predicted sodium excretion correlated strongly with actual 24-h sodium excretion, both for the dipstick method (r = 0.71; observer 1 and r = 0.65; observer 2; both P < 0.001), and the laboratory method (r = 0.86, P < 0.001). PM samples also differentiated subjects with sodium excretion <100 mEq/day vs. > or =100 mEq/day (sensitivity and specificity: dipstick method: 83 and 82%, respectively for observer 1, 89 and 77%, respectively, for observer 2; laboratory method: 100 and 82%, respectively). AM samples and random samples correlated less strongly.

CONCLUSION

The dipstick method appears promising as a convenient and inexpensive means to serially assess sodium excretion.

Are overnight urinary indicators associated with morning blood pressure in the elderly?

Recent reports suggest that high blood pressure (BP) during the night is associated with hypertensive organ damage, and that increased BP in the morning is closely related to the incidence of stroke and ischemic heart disease. The aim of this study was to investigate the relationships between overnight urinary indicators and 24-hour (24-h) BP, especially in the morning and during sleep in the elderly. A total of 85 volunteers (males 43, females 42), aged between 51 and 76 years and not taking any antihypertensive medications, participated in this study. Their 24-h BP was measured by ambulatory BP monitoring every 30-minute using a TERUMO ES-H531 system. Overnight urine samples were collected using a proportional urine-sampling device, Urine mate P. Overnight sodium (UNa(n)) and potassium (UKn) excretions were measured by an ion electrode method. Simple linear regression analyses showed that systolic blood pressure (SBP) in the morning and diastolic blood pressure (DBP) during sleep were negatively related with overnight urinary weight standardized for body weight (UW(n)/BW). Multiple regression analyses showed that SBP during the morning and during sleep was positively related to UNa(n) and negatively related to UW(n)/BW. We also found a negative relationship between SBP during sleep and UK(n). The study suggested that urine weight adjusted for BW was negatively related with 24-h BP, especially morning BP. Sodium excretion combined with a large volume of urine proportional to body weight may prevent increases in BP, especially in the morning.

Dual blockade of angiotensin II with enalapril and losartan reduces proteinuria in hypertensive patients with type 2 diabetes

In this study we evaluated the effect of a dual blockade with enalapril and losartan on the reduction of overt macroproteinuria and its potential mechanism(s) in hypertensive patients with type 2 diabetes. Twenty-six hypertensive patients with type 2 diabetes at the baseline were administered 5 mg of enalapril once daily for 12 weeks. At the beginning of the study, the subjects were assigned to receive an add-on of 50 mg of losartan once daily or 5 mg of enalapril once daily for another 12 weeks. Blood samples were collected at the baseline, at the beginning, and at the end of the study for the measurement of laboratory parameters, and these data, including blood pressure, were compared between the two groups. Treatment with 5 mg of enalapril significantly decreased the systolic blood pressure level in both groups, and the addition of losartan and/or enalapril further decreased the levels. There was no difference in blood pressure between the two groups. However, the addition of losartan, but not enalapril, significantly decreased the urinary protein excretion level, plasma aldosterone, and hypersensitive-C-reactive protein at the end of the study. The results established that the dual blockade of angiotensin II with enalapril and losartan has a greater clinical benefit for high-risk patients with hypertension and advanced diabetic nephropathy.

Self-monitoring of home blood pressure with estimation of daily salt intake using a new electrical device

We investigated a simple device to monitor daily salt intake at home and examined the relationship between salt excretion and morning blood pressure in order to enable patients to better manage daily salt intake and hypertension. The correlation between 24-h urinary salt excretion and measured value with salt monitor from overnight urine was significant (n = 224, r = 0.72, P < 0.001). A total of 46 volunteers participated for more than 3 weeks by measuring daily salt intake and morning blood pressure. The relationship between predicted daily salt excretion and blood pressure was examined with use of 3-day moving average. Mean salt excretion and systolic blood pressure (SBP) significantly decreased by the end of the trial (i.e., salt excretion decreased from 158+/-31 to 149+/-30 mmol/day and SBP from 137+/-17 to 133+/-16 mm Hg). Of 46 participants, 18 (39%) had a significant correlation between predicted daily salt excretion and blood pressure (r > 0.4, P < 0.05, n > 21), indicating sodium sensitivity. An additional 17% had a positive correlation that did not reach statistical significance (0.2 < r < or = 0.4), and the remaining 44% had no correlation (r < or = 0.2). Mean decrease in blood pressure per decrease in salt (g) (17 mmol) intake in the 18 participants with a significant correlation was 3.3 mm Hg (SBP) and 1.5 mm Hg (diastolic blood pressure), which was higher than that reported for other studies. Hypertensive patients not using medication showed the largest decrease. We conclude that daily monitoring of salt intake and morning blood pressure will be useful for management of hypertension.