Estimation of 24-hour sodium excretion from spot urine samples

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.

Effectiveness of a Communication for Behavioral Impact (COMBI) Intervention to Reduce Salt Intake in a Vietnamese Province Based on Estimations From Spot Urine Samples

This study evaluated the effectiveness of the Communication for Behavioral Impact (COMBI)–Eat Less Salt intervention conducted in Viet Tri, Vietnam. The behavior change intervention was implemented in four wards and four communes for one year, which included mass media communication, school interventions, community programs, and focus on high‐risk groups. Mean sodium excretion was estimated from spot urine samples using different equations. A subsample provided 24‐hour urine to validate estimates from spot urine. Information about salt‐related knowledge and behaviors was also collected. There were 513 participants at both baseline and follow‐up. Mean sodium excretion estimated from spot urines fell significantly from 8.48 g/d at baseline to 8.05 g/d at follow‐up (P=.001). All spot equations demonstrated a significant reduction in sodium levels; however, the change was smaller than the measured 24‐hour urine. Participants showed improved knowledge and behaviors following the intervention. The COMBI intervention was effective in lowering average population salt intake and improving knowledge and behaviors.

Association of Urinary Sodium Excretion With Insulin Resistance in Korean Adolescents: Results From the Korea National Health and Nutrition Examination Survey 2009-2010

High sodium intake is a well-known risk factor for elevated blood pressure and is responsible for a higher incidence of cardiovascular events. Reports have suggested an association of sodium intake with insulin resistance (IR) and type 2 diabetes mellitus in adults. However, evidence on an association between sodium intake assessed on the basis of urinary sodium excretion and IR in adolescents is scarce. The present study aimed at investigating the association between urinary sodium excretion and IR among South Korean adolescents.This population-based, cross-sectional study analyzed the data obtained from the Korea National Health and Nutrition Examination Survey (KNHANES) 2009 to 2010. The data of a total of 1353 adolescents (779 boys and 574 girls) were included in the final analysis. Spot urine samples were collected, and urinary sodium excretion was estimated by using the urinary sodium concentration (U[Na]), U[Na] to urinary creatinine ratio (U[Na]/Cr), and U[Na] to specific gravity unit (SGU) ratio (U[Na]/SGU). IR was assessed by using the homeostasis model assessment of IR (HOMA-IR). Hierarchical multivariable logistic regression analysis was performed to assess the risk for a high HOMA-IR according to urinary sodium excretion.The mean levels of U[Na], U[Na]/Cr, and U[Na]/SGU were significantly higher in subjects in the highest HOMA-IR quartile (Q4) than in subjects in the lowest, second, or third quartiles (Q1-3) of HOMA-IR. The mean values of HOMA-IR and several cardiometabolic parameters tended to progressively increase with the U[Na], U[Na]/Cr, and U[Na]/SGU quartiles. Q3 of U[Na] was at a significantly higher risk than Q1 of U[Na] of an association with Q4 of HOMA-IR, after adjustment for confounding variables. Q3 and Q4 of U[Na]/Cr and U[Na]/SGU, respectively, had significantly higher risks, than the respective Q1s, of an association with Q4 of HOMA-IR. The risk of an association with Q4 of HOMA-IR demonstrated significantly increasing trends with increasing quartiles of U[Na], U[Na]/Cr, and U[Na]/SGU irrespective of confounding factors.Urinary sodium excretion was positively associated with IR in South Korean adolescents. The monitoring and control of urinary sodium excretion may be recommended as an important intervention for the prevention of IR and related diseases in adolescents.

The relationship between sodium concentrations in spot urine and blood pressure increases: a prospective study of Japanese general population: the Circulatory Risk in Communities Study (CIRCS)

Background

Although several cross-sectional and intervention studies showed that sodium intake or excretion was associated with blood pressure levels, no prospective study has examined the long-term association between sodium excretion in spot urine and blood pressure changes.

Methods

We conducted a prospective study of 889 normotensive subjects (295 men and 594 women, mean age 57.3 years) who underwent the baseline survey including spot urine test in 2005 and the follow-up survey in 2009 to 2011 (mean follow-up period: 5.8 years). We examined the association between sodium concentration in spot urine, a validated index of sodium excretion occurring over 24-h, and blood pressure changes between baseline and follow-up survey in all, non-overweight (body mass index(BMI) ≤ 25 kg/m²) and overweight normotensives.

Results

For all subjects, sodium concentrations in spot urine were not associated with either systolic or diastolic blood pressure changes. When stratified by BMI at baseline survey, sodium concentrations were positively associated with systolic blood pressure changes in non-overweight subjects, but not in overweight subjects. After adjustment for age, sex, BMI, alcohol intake status, current smoking and estimated glomerular filtration rate, the multivariable-adjusted mean values of the systolic blood pressure change among non-overweight subjects was +7.3 mmHg in the highest quartiles of sodium concentrations, while it was +3.9 mmHg in the lowest quartile (P for difference = 0.021, P for trend = 0.040). After further adjustment of baseline blood pressure levels, the association was slightly weakened; the multivariable-adjusted mean values of the systolic blood pressure changes were +7.0 mmHg and +4.2 mmHg (P for difference = 0.047, P for trend = 0.071).

Conclusions

High sodium concentrations in spot urine were associated with subsequent systolic blood pressure increases among non-overweight normotensive individuals. (272 words)

Electronic supplementary material

The online version of this article (doi:10.1186/s12872-016-0219-1) contains supplementary material, which is available to authorized users.

Estudo de validação das equações de Tanaka e de Kawasaki para estimar a excreção diária de sódio através da coleta da urina casual

RESUMO: Objetivo: Validar as fórmulas de Tanaka e Kawasaki para cálculo do consumo de sal pela relação sódio/creatinina na urina casual. Métodos: Foram estudados 272 adultos (20 - 69 anos, 52,6% de mulheres) com coleta urinária de 24 h e duas coletas casuais no mesmo dia (em jejum - casual 1 - e fora do jejum - casual 2). Antropometria, pressão arterial e coleta de sangue foram obtidos no mesmo dia. A concordância entre o consumo de sal estimado pela urina de 24 h e pela urina casual foi feita por Pearson (r) e Bland & Altman. Resultados: O consumo médio de sal medido pela urina de 24 h foi de 10,4 ± 5,3 g/dia. A correlação entre a excreção de sódio na urina de 24 h e a estimada pela urina casual 1 ou 2, respectivamente, foi apenas moderada, tanto por Tanaka (r = 0,51 e r = 0,55; p < 0,001) como por Kawasaki (r = 0,52 e r = 0,54; p < 0,001). Observa-se subestimação crescente dos valores estimados em relação ao medido com o aumento do consumo de sal pela fórmula de Tanaka e, ao contrário, superestimação ao usar a fórmula de Kawasaki. As fórmulas estimam adequadamente o consumo diário de sal (diferença entre sal medido e estimado de, no máximo, 1 g/dia) somente com consumo entre 9 - 12 g/dia (Tanaka) e 12 - 18 g/dia (Kawasaki). Conclusão: A coleta de urina casual estima adequadamente o consumo de sal apenas nos indivíduos próximos à média populacional.

Validation of the Spot Urine in Evaluating 24-Hour Sodium Excretion in Chinese Hypertension Patients

BACKGROUND

The spot urine method as an alternative approach in estimating daily urine sodium excretion has been proposed for many years. Kawasaki has created an equation to predict daily urinary sodium excretion using second morning urine (SMU) samples which was obtained before breakfast after initial voiding upon arising. Tanaka has developed another equation by examining spot urine samples submitted at random times during the day. A newly published study proposed that the "PM sample," collected in the late afternoon or early evening before dinner, showed a stronger relationship with actual sodium excretion. We aimed to verify the effectiveness of these methods in evaluating 24-hour urinary sodium in Chinese hypertensive patients.

METHODS

A total of 334 hypertensive participants were eligible to participate in this study. A total of 222 patients provided qualified SMU samples, Post Meridiem (PM) samples, and complete 24-hour urine collections.

RESULTS

Biases using the Kawasaki formula were 2.1 mmol/day for the SMU specimens; for the Tanaka equation, biases of SMU and PM samples were 21.1 and 30.1 mmol/day, respectively. The highest intraclass correlation coefficient (ICC) was 0.64 when the Kawasaki formula was used in PM specimens, with the lowest ICC 0.17 when it is used in SMUs.

CONCLUSIONS

Spot urine method is acceptable for estimating 24-hour urinary sodium excretion in hypertensive individuals. Kawasaki's formula is useful for estimating population mean levels of sodium excretion from SMU, although it is not suitable for estimating individual sodium excretion.

Sodium Intake and Socioeconomic Status as Risk Factors for Development of Age-Related Cataracts: The Korea National Health and Nutrition Examination Survey

Purpose

Cataract is a very prevalent ocular disorder, and environmental risk factors for age-related cataracts have been widely investigated. We aimed to evaluate an association of dietary sodium intake and socioeconomic factors with the development of age-related cataracts.

Methods

A cross-sectional case-control study based on the 2008–2011 Korea National Health and Nutrition Examination Survey. Dietary sodium intake was estimated using urinary sodium to creatinine ratio (U[Na⁺]/Cr).

Results

Among a total 12,693 participants, 2,687 (21.1%) had cataracts and 10,006 patients without cataracts served as controls. The prevalence of cataracts increased with age and quartiles of U[Na⁺]/Cr (p for trend < 0.001). Multivariate logistic regression analyses revealed that factors related to the development of cataracts were age ≥ 50 years (adjusted odds ratio [aOR] 15.34, 95% confidence interval [CI] 13.31‒17.69), low income (aOR 1.85, 95% CI 1.64–2.09), low educational attainment (aOR 1.76, 95% CI 1.57–1.96), and high sodium intake (U[Na⁺]/Cr > 16.4 mmol/mmol; aOR 1.29, 95% CI 1.16–1.44). In a subgroup analysis, a robust effect on cataracts across U[Na⁺]/Cr quartiles was observed in patients ≥ 50 years of age (aOR 1.11, 95% CI 1.04–1.18), though not in younger patients (aOR 1.06, 95% CI 0.96–1.17).

Conclusions

Our results suggest that high sodium intake and low socioeconomic status may affect the development of cataracts, and that a low-salt diet could be helpful for the prevention of cataracts in an older population. Furthermore, efforts to close gaps in health services due to socioeconomic factors may contribute to a reduction in the prevalence of cataracts.

Sodium intake reduction efforts in Lebanon

Sodium intake reduction efforts in Lebanon are quite recent and have just started to take effect on the national level. Starting out from an academic institution, the Lebanese Action on Sodium and Health (LASH) campaign was established to counter the increasing prevalence of hypertension and associated adverse health effects. The campaign's strategy was based on four pillars: research, health communication, advocacy, and monitoring. The LASH group set out with determining: baseline sodium intake of the population, main sources of sodium intake, and the knowledge, attitudes, and behaviors (KAB) of the population as a situation analysis that prompts for action. This gave LASH tangible evidence of the magnitude of the problem and the need for the government, the food industry, and the consumers, to be mobilized to take part in devising a solution. Currently, Lebanon is at a stage of technically working to reduce the sodium content in the major sources of sodium, namely local bread and bread-like products. The next steps will include implementation of a plan for monitoring industry compliance, while studying other food targets, including dairy products and processed meat. Meanwhile, the health communication plan is ongoing and the Salt Awareness Week is celebrated every year with media appearances of LASH researchers to raise the issue to the public eye.

High sodium intake: review of recent issues on its association with cardiovascular events and measurement methods

There has been a long-known association between high dietary sodium intake and hypertension, as well as the increased risk of cardiovascular disease. Reduction of sodium intake is a major challenge for public health. Recently, there have been several controversial large population-based studies regarding the current recommendation for dietary sodium intake. Although these studies were performed in a large population, they aroused controversies because they had a flaw in the study design and methods. In addition, knowledge of the advantages and disadvantages of the methods is essential in order to obtain an accurate estimation of sodium intake. I have reviewed the current literatures on the association between sodium intake and cardiovascular events, as well as the methods for the estimation of sodium intake.

Estimating the population distribution of usual 24-hour sodium excretion from timed urine void specimens using a statistical approach accounting for correlated measurement errors

BACKGROUND

High US sodium intake and national reduction efforts necessitate developing a feasible and valid monitoring method across the distribution of low-to-high sodium intake.

OBJECTIVE

We examined a statistical approach using timed urine voids to estimate the population distribution of usual 24-h sodium excretion.

METHODS

A sample of 407 adults, aged 18-39 y (54% female, 48% black), collected each void in a separate container for 24 h; 133 repeated the procedure 4-11 d later. Four timed voids (morning, afternoon, evening, overnight) were selected from each 24-h collection. We developed gender-specific equations to calibrate total sodium excreted in each of the one-void (e.g., morning) and combined two-void (e.g., morning + afternoon) urines to 24-h sodium excretion. The calibrated sodium excretions were used to estimate the population distribution of usual 24-h sodium excretion. Participants were then randomly assigned to modeling (n = 160) or validation (n = 247) groups to examine the bias in estimated population percentiles.

RESULTS

Median bias in predicting selected percentiles (5th, 25th, 50th, 75th, 95th) of usual 24-h sodium excretion with one-void urines ranged from -367 to 284 mg (-7.7 to 12.2% of the observed usual excretions) for men and -604 to 486 mg (-14.6 to 23.7%) for women, and with two-void urines from -338 to 263 mg (-6.9 to 10.4%) and -166 to 153 mg (-4.1 to 8.1%), respectively. Four of the 6 two-void urine combinations produced no significant bias in predicting selected percentiles.

CONCLUSIONS

Our approach to estimate the population usual 24-h sodium excretion, which uses calibrated timed-void sodium to account for day-to-day variation and covariance between measurement errors, produced percentile estimates with relatively low biases across low-to-high sodium excretions. This may provide a low-burden, low-cost alternative to 24-h collections in monitoring population sodium intake among healthy young adults and merits further investigation in other population subgroups.

Personalizing the diuretic treatment of hypertension: the need for more clinical and research attention

Neither randomized controlled trials nor efforts to identify genetic markers have been helpful with regard to the goal of individualizing diuretic therapy in the treatment of hypertension, a goal that receives little clinical or research attention. This review will examine, and bring attention to, the considerable yet overlooked information relevant to individualizing diuretic therapy. It will bring attention to clinical, biochemical, and pharmacological clues that can be helpful in identifying who is likely to respond to a diuretic, who needs a stronger diuretic regimen, which diuretic to prescribe, and how to minimize adverse effects. New directions for clinical research aimed at individualizing use in hypertension will be explored. Research and clinical attention to the goal of individualizing diuretic treatment in hypertension need to be renewed, to help us achieve greater hypertension control with fewer adverse effects and lower costs.

Is complying with the recommendations of sodium intake beneficial for health in individuals at high cardiovascular risk? Findings from the PREDIMED study

BACKGROUND

Excess sodium intake is associated with high blood pressure, a major risk factor for cardiovascular disease (CVD). It is unknown whether decreasing sodium intake to <2300 mg/d has an effect on CVD or all-cause mortality.

OBJECTIVE

The objective was to assess whether reductions in sodium intake to <2300 mg/d were associated with either an increased or a decreased risk of fatal and nonfatal CVD and all-cause mortality.

DESIGN

This observational prospective study of the PREvención con DIeta MEDiterránea (PREDIMED) trial included 3982 participants at high CVD risk. Sodium intake was evaluated with a validated food-frequency questionnaire and categorized as low (<1500 mg/d), intermediate (≥1500 to ≤2300 mg/d), high (>2300 to ≤3400 mg/d), or very high (>3400 mg/d). Subsequently, 1-y and 3-y changes in sodium intake were calculated. Multivariate relative risks were assessed by using Cox proportional hazards ratios. Marginal structural models with inverse probability weighting were used to test the effect of changes in sodium intake and the Mediterranean diet (MedDiet).

RESULTS

We documented 125 CVD events and 131 deaths after a 4.8-y median follow-up. Sodium intake <2300 mg/d was associated with a lower risk of all-cause mortality: 48% (HR: 0.52; 95% CI: 0.30, 0.91; P = 0.02) and 49% (HR: 0.51; 95% CI: 0.26, 0.98; P = 0.04) after 1 and 3 y, respectively. Increasing sodium intake after 1 y was associated with a 72% (HR: 1.72; 95% CI: 1.01, 2.91; P = 0.04) higher risk of CVD events. The incidence rate of CVD was reduced for those who reduced their sodium intake and were randomly assigned to MedDiet interventions [4.1/10,000 (95% CI: 3.1, 8.0) compared with 4.4/10,000 (95% CI: 2.7, 12.4) person-years; P = 0.002].

CONCLUSIONS

Decreasing sodium intake to <2300 mg/d was associated with a reduced risk of all-cause mortality, whereas increasing the intake to >2300 mg/d was associated with a higher risk of CVD. Our observational data suggest that sodium intake <2300 mg/d was associated with an enhanced beneficial effect of the MedDiet on CVD. These results should be interpreted with caution, and other confirmatory studies are necessary.

Evaluation of random urine sodium and potassium compensated by creatinine as possible alternative markers for 24 hours urinary sodium and potassium excretion

Sodium and potassium intake was assessed on the basis of its respective excretion levels in 24 hr urine samples. However, owing to the inconvenience of collection, we evaluated random spot urine for alternative sodium and potassium excretion markers. We included 250 patients who submitted 24 hr- and spot urine for clinical tests. However, 22 patients who showed 24 hr urine creatinine excretion levels <500 mg/day were excluded, because these samples possibly resulted from incomplete urine collection. Moreover, 24 patients were excluded because of their use of diuretics during the urine collection period. We observed significant correlations between 24 hr urine sodium excretion and both the sodium/creatinine (r=0.34, P<0.0001) and the sodium/specific gravity unit (SGU) ratios (r=0.19, P=0.007) in random urine samples. Similarly, 24 hr urine potassium excretion and both the spot urine potassium/creatinine (r=0.47, P<0.0001) and potassium/SGU ratios (r=0.28, P<0.0001) were significantly correlated. Although the estimated sodium/creatinine and potassium/creatinine ratios showed a significant correlation with 24 hr urine sodium and potassium excretion, respectively, further studies are required to develop a spot urine test for individualized monitoring of sodium and potassium excretion.

Normalisation of urinary biomarkers to creatinine for clinical practice and research--when and why

Acute kidney injury (AKI) and chronic kidney disease (CKD) are major health problems. Urinary biomarkers have both diagnostic and prognostic utility in AKI and CKD. However, how biomarker excretion rates should be reported, especially whether they should be normalised to urinary creatinine concentration (uCr), is controversial. Some studies suggest that normalisation to uCr may be inappropriate at times, as urinary creatinine excretion rate may vary greatly, depending on the situation. Notably, recent studies suggest that while normalisation of values to UCr may be valid for the evaluation of CKD and prediction of AKI sequelae and occurrences, it could be inappropriate for the diagnosis of AKI, or in the presence of certain acute kidney disease states.

Sodium intake is associated with increased disease activity in multiple sclerosis

BACKGROUND

Recently, salt has been shown to modulate the differentiation of human and mouse Th17 cells and mice that were fed a high-sodium diet were described to develop more aggressive courses of experimental autoimmune encephalomyelitis. However, the role of sodium intake in multiple sclerosis (MS) has not been addressed. We aimed to investigate the relationship between salt consumption and clinical and radiological disease activity in MS.

METHODS

We conducted an observational study in which sodium intake was estimated from sodium excretion in urine samples from a cohort of 70 relapsing-remitting patients with MS who were followed for 2 years. The effect of sodium intake in MS disease activity was estimated using regression analysis. We then replicated our findings in a separate group of 52 patients with MS.

RESULTS

We found a positive correlation between exacerbation rates and sodium intake in a multivariate model adjusted for age, gender, disease duration, smoking status, vitamin D levels, body mass index and treatment. We found an exacerbation rate that was 2.75-fold (95% CI 1.3 to 5.8) or 3.95-fold (95% CI 1.4 to 11.2) higher in patients with medium or high sodium intakes compared with the low-intake group. Additionally, individuals with high-sodium intake had a 3.4-fold greater chance of developing a new lesion on the MRI and on average had eight more T2 lesions on MRI. A similar relationship was found in the independent replication group.

CONCLUSIONS

Our results suggest that a higher sodium intake is associated with increased clinical and radiological disease activity in patients with MS.

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.

Evaluation of using spot urine to replace 24 h urine sodium and potassium excretions

OBJECTIVE

The most accurate method to estimate Na and K intakes is to determine 24 h urinary excretions of these minerals. However, collecting 24 h urine is burdensome. Therefore it was studied whether spot urine could be used to replace 24 h urine samples.

DESIGN

Participants collected 24 h urine and kept one voiding sample separate. Na, K and creatinine concentrations were analysed in both 24 h and spot urine samples. Also 24 h excretions of Na and K were predicted from spot urine concentrations using the Tanaka and Danish methods.

SETTING

In 2011 and 2012, urine samples were collected and brought to the study centre at Wageningen University, the Netherlands.

SUBJECTS

Women (n 147) aged 19-26 years.

RESULTS

According to p-aminobenzoic acid excretions, 127 urine collections were complete. Correlations of Na:creatinine, K:creatinine and Na:K between spot urine and 24 h urine were 0·68, 0·57 and 0·64, respectively. Mean 24 h Na excretion predicted with the Tanaka method was higher (difference 21·2 mmol/d, P<0·001) than the measured excretion of 131·6 mmol/d and mean 24 h Na excretion predicted with the Danish method was similar (difference 3·2 mmol/d, P=0·417) to the measured excretion. The mean 24 h K excretion predicted with the Tanaka method was higher (difference 13·6 mmol/d, P<0·001) than the measured excretion of 66·8 mmol/d. Bland-Altman plots showed large individual differences between predicted and measured 24 h Na and K excretions.

CONCLUSIONS

The ratios of Na:creatinine and K:creatinine in spot urine were reasonably well associated with their respective ratios in 24 h urine and appear to predict mean 24 h Na excretion of these young, Caucasian women.

Development of a formula for estimation of sodium intake from spot urine in people with chronic kidney disease

BACKGROUND/AIMS

High sodium intake is associated with adverse cardiovascular and renal outcomes in people with chronic kidney disease (CKD), and simple methods to facilitate assessment of sodium intake are required. The objective of this study was to develop a new formula to estimate 24-hour urinary sodium (24hUNa) excretion from urinary Na concentration measured on an early morning urine specimen (EM UNa).

METHODS

Seventy participants from a prospective cohort of patients with CKD stage 3 in primary care, the Renal Risk in Derby (RRID) study, agreed to collect an additional EM UNa on the day after completing a 24-hour urine collection. A formula to estimate 24hUNa from EM UNa and body weight was developed using the coefficients from a multivariable linear regression equation. The accuracy of the formula was tested by calculating the P30 (proportion of estimates within 30% of measured sodium exection), and the ability of the estimated 24hUNa to discriminate between measured sodium intake above or below 100 mmol/day was assessed by receiver operating characteristic (ROC) curve. A Bland-Altman plot was used to estimate the bias and limits of agreement between estimated and measured 24hUNa. Seventy-four additional paired 24hUNa and EM UNa from 50 CKD stage 3 patients in the RRID study were used to validate the formula.

RESULTS

The mean difference between measured and estimated 24hUNa was 2.08 mmol/day. Measured and estimated 24hUNa were significantly correlated (r = 0.55; p < 0.001) but accuracy of estimated 24hUNa was low (P30 = 60%). Analysis of the ROC curve with a cut-off point >100 mmol/day yielded an area under the curve of 0.668, sensitivity of 0.85 and specificity of 0.52.

CONCLUSIONS

We have developed a simple formula to identify people with a high sodium intake from EM UNa, suitable for use in large-cohort or population studies.

Estimated 24-hour urine sodium excretion is correlated with blood pressure in Korean population: 2009-2011 Korean National Health and Nutritional Examination Survey

No large-scale studies have investigated the association between salt intake and hypertension in Korean population. To investigate the relationship of blood pressure to salt consumption, we analyzed data from 19,476 participants in the 2009-2011 Korean National Health and Nutritional Examination Survey (KNHANES). Urinary sodium excretion over 24-hr (24HUNa) was estimated from spot urine tests using Tanaka's equation. The study subjects were stratified into hypertensive and normotensive groups. Hypertensive participants (n=6,552, 33.6%) had higher estimated 24HUNa, 150.4±38.8 mEq/day, than normotensive participants, 140.5±34.6 mEq/day (P<0.001). The association between 24HUNa and blood pressure outcomes was not affected by adjustment for other risk factors for hypertension (odds ratio 0.001; 95% confidence interval 0.001-0.003; P<0.001). Increases in 24HUNa of 100 mEq/day were associated with a 6.1±0.3/2.9±0.2 mmHg increase in systolic/diastolic blood pressure in all participants. This effect was stronger in hypertensive participants (increase of 8.1±0.5/3.4±0.3 mmHg per 100 mEq/day) and smaller in normotensive participants (2.9±0.3/1.3±0.2 mmHg). These results support recommendations for low salt intake in Korean population to prevent and control adverse blood pressure levels.

Estimation of 24-hour urinary sodium excretion using spot urine samples

The present study evaluated the reliability of equations using spot urine (SU) samples in the estimation of 24-hour urine sodium excretion (24-HUNa). Equations estimating 24-HUNa from SU samples were derived from first-morning SU of 101 participants (52.4 ± 11.1 years, range 24–70 years). Equations developed by us and other investigators were validated with SU samples from a separate group of participants (n = 224, 51.0 ± 10.9 years, range 24–70 years). Linear, quadratic, and cubic equations were derived from first-morning SU samples because these samples had a sodium/creatinine ratio having the highest correlation coefficient for 24-HUNa/creatinine ratio (r = 0.728, p < 0.001). In the validation group, the estimated 24-HUNa showed significant correlations with measured 24-HUNa values. The estimated 24-HUNa by the linear, quadratic, and cubic equations developed from our study were not significantly different from measured 24-HUNa, while estimated 24-HUNa by previously developed equations were significantly different from measured 24-HUNa values. The limits of agreement between measured and estimated 24-HUNa by six equations exceeded 100 mmol/24-hour in the Bland-Altman analysis. All equations showed a tendency of under- or over-estimation of 24-HUNa, depending on the level of measured 24-HUNa. Estimation of 24-HUNa from single SU by equations as tested in the present study was found to be inadequate for the estimation of an individual’s 24-HUNa.

Methodological Issues in Cohort Studies That Relate Sodium Intake to Cardiovascular Disease Outcomes

Background—

The results of cohort studies relating sodium (Na) intake to blood pressure–related cardiovascular disease (CVD) are inconsistent. To understand whether methodological issues account for the inconsistency, we reviewed the quality of these studies.

Methods and Results—

We reviewed cohort studies that examined the association between Na and CVD. We then identified methodological issues with greatest potential to alter the direction of association (reverse causality, systematic error in Na assessment), some potential to alter the direction of association (residual confounding, inadequate follow-up), and the potential to yield false null results (random error in Na assessment, insufficient power). We included 26 studies with 31 independent analyses. Of these, 13 found direct associations between Na and CVD, 8 found inverse associations, 2 found J-shaped associations, and 8 found null associations only. On average there were 3 to 4 methodological issues per study. Issues with greater potential to alter the direction of association were present in all but 1 of the 26 studies (systematic error, 22; reverse causality, 16). Issues with lesser potential to alter the direction of association were present in 18 studies, whereas those with potential to yield false null results were present in 23.

Conclusions—

Methodological issues may account for the inconsistent findings in currently available observational studies relating Na to CVD. Until well-designed cohort studies in the general population are available, it remains appropriate to base Na guidelines on the robust body of evidence linking Na with elevated blood pressure and the few existing general population trials of the effects of Na reduction on CVD.

Validity of predictive equations for 24-h urinary sodium excretion in adults aged 18-39 y

BACKGROUND

Collecting a 24-h urine sample is recommended for monitoring the mean population sodium intake, but implementation can be difficult.

OBJECTIVE

The objective was to assess the validity of published equations by using spot urinary sodium concentrations to predict 24-h sodium excretion.

DESIGN

This was a cross-sectional study, conducted from June to August 2011 in metropolitan Washington, DC, of 407 adults aged 18-39 y, 48% black, who collected each urine void in a separate container for 24 h. Four timed voids (morning, afternoon, evening, and overnight) were selected from each 24-h collection. Published equations were used to predict 24-h sodium excretion with spot urine by specimen timing and race-sex subgroups. We examined mean differences with measured 24-h sodium excretion (bias) and individual differences with the use of Bland-Altman plots.

RESULTS

Across equations and specimens, mean bias in predicting 24-h sodium excretion for all participants ranged from -267 to 1300 mg (Kawasaki equation). Bias was least with International Cooperative Study on Salt, Other Factors, and Blood Pressure (INTERSALT) equations with morning (-165 mg; 95% CI: -295, 36 mg), afternoon (-90 mg; -208, 28 mg), and evening (-120 mg; -230, -11 mg) specimens. With overnight specimens, mean bias was least when the Tanaka (-23 mg; 95% CI: -141, 95 mg) or Mage (-145 mg; -314, 25 mg) equations were used but was statistically significant when using the Tanaka equations among females (216 to 243 mg) and the Mage equations among races other than black (-554 to -372 mg). Significant over- and underprediction occurred across individual sodium excretion concentrations.

CONCLUSIONS

Using a single spot urine, INTERSALT equations may provide the least biased information about population mean sodium intakes among young US adults. None of the equations evaluated provided unbiased estimates of individual 24-h sodium excretion.

Effects of an isocaloric healthy Nordic diet on ambulatory blood pressure in metabolic syndrome: a randomized SYSDIET sub-study

BACKGROUND/OBJECTIVES

Dietary pattern is central in the prevention of hypertension and blood pressure (BP)-related diseases. A diet based on healthy Nordic foods may have a favourable impact on BP. The objective was to clarify whether a Nordic alternative for a healthy food pattern would have beneficial effects on ambulatory BP in subjects with metabolic syndrome (MetS).

SUBJECTS/METHODS

In total, 37 subjects were randomized to either a healthy Nordic diet or a control diet. A healthy Nordic diet embraced whole grains, rapeseed oil, berries, fruits, vegetables, fish, nuts and low-fat dairy products of Nordic origin. The mean nutrient intake in the Nordic countries formed the control diet, embracing wheat products, dairy fat-based spread and a lower intake of fruits, vegetables and fish. Diets were isoenergetic. Ambulatory BP was monitored and 24-h urine was collected before and after 12 weeks of intervention.

RESULTS

After 12 weeks, ambulatory diastolic BP (-4.4 mm Hg; P=0.001) and mean arterial pressure (-4.2 mm Hg; P=0.006) were lowered by the healthy Nordic diet compared with the control diet, whereas changes in ambulatory systolic BP did not differ significantly between diets (-3.5 mm Hg; P=0.122). Heart rate tended to be lower in those on the healthy Nordic diet (P=0.057). Urinary sodium and potassium excretions were unaffected by diets and consequently not associated with the healthy Nordic diet-induced lowering of BP.

CONCLUSIONS

Consumption of Nordic varieties of health-enhancing foods for 12 weeks decreased diastolic ambulatory BP and mean arterial pressure in subjects with features of MetS during weight-stable condition, suggesting beneficial effects of a healthy Nordic dietary pattern on ambulatory BP.

Urinary biomarkers of smokers' exposure to tobacco smoke constituents in tobacco products assessment: a fit for purpose approach

There are established guidelines for bioanalytical assay validation and qualification of biomarkers. In this review, they were applied to a panel of urinary biomarkers of tobacco smoke exposure as part of a "fit for purpose" approach to the assessment of smoke constituents exposure in groups of tobacco product smokers. Clinical studies have allowed the identification of a group of tobacco exposure biomarkers demonstrating a good doseresponse relationship whilst others such as dihydroxybutyl mercapturic acid and 2-carboxy-1-methylethylmercapturic acid - did not reproducibly discriminate smokers and non-smokers. Furthermore, there are currently no agreed common reference standards to measure absolute concentrations and few inter-laboratory trials have been performed to establish consensus values for interim standards. Thus, we also discuss in this review additional requirements for the generation of robust data on urinary biomarkers, including toxicant metabolism and disposition, method validation and qualification for use in tobacco products comparison studies.

Determinants and changes associated with aldosterone breakthrough after angiotensin II receptor blockade in patients with type 2 diabetes with overt nephropathy

BACKGROUND AND OBJECTIVES

Inhibition of the renin-angiotensin-aldosterone system decreases proteinuria and slows estimated GFR decline in patients with type 2 diabetes mellitus with overt nephropathy. Serum aldosterone levels may increase during renin-angiotensin-aldosterone system blockade. The determinants and consequences of this aldosterone breakthrough remain unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study examined the incidence, determinants, and changes associated with aldosterone breakthrough in a posthoc analysis of a randomized study that compared the effect of two angiotensin II receptor blockers in patients with type 2 diabetes mellitus with overt nephropathy.

RESULTS

Of 567 of 860 participants included in this posthoc analysis, 28% of participants developed aldosterone breakthrough, which was defined by an increase greater than 10% over baseline values of serum aldosterone levels after 1 year of angiotensin II receptor blocker treatment. Factors independently associated with aldosterone breakthrough at 1 year were lower serum aldosterone and potassium levels at baseline, higher decreases in sodium intake, systolic BP, and estimated GFR from baseline to 1 year, and use of losartan versus telmisartan. Aldosterone breakthrough at 6 months was not sustained at 1 year in 69% of cases, and it did not predict estimated GFR decrease and proteinuria increase between 6 months and 1 year.

CONCLUSIONS

Aldosterone breakthrough is a frequent event 1 year after initiating renin-angiotensin-aldosterone system blockade, particularly in participants exposed to intensive lowering of BP with sodium depletion and short-acting angiotensin II receptor blockers. Short-term serum aldosterone level increases at 6 months are not associated with negative kidney outcomes between 6 months and 1 year.

Urinary excretion of sodium, potassium, and chloride, but not iodine, varies by timing of collection in a 24-hour calibration study

Because of the logistic complexity, excessive respondent burden, and high cost of conducting 24-h urine collections in a national survey, alternative strategies to monitor sodium intake at the population level need to be evaluated. We conducted a calibration study to assess the ability to characterize sodium intake from timed-spot urine samples calibrated to a 24-h urine collection. In this report, we described the overall design and basic results of the study. Adults aged 18-39 y were recruited to collect urine for a 24-h period, placing each void in a separate container. Four timed-spot specimens (morning, afternoon, evening, and overnight) and the 24-h collection were analyzed for sodium, potassium, chloride, creatinine, and iodine. Of 481 eligible persons, 407 (54% female, 48% black) completed a 24-h urine collection. A subsample (n = 133) collected a second 24-h urine 4-11 d later. Mean sodium excretion was 3.54 ± 1.51 g/d for males and 3.09 ± 1.26 g/d for females. Sensitivity analysis excluding those who did not meet the expected creatinine excretion criterion showed the same results. Day-to-day variability for sodium, potassium, chloride, and iodine was observed among those collecting two 24-h urine samples (CV = 16-29% for 24-h urine samples and 21-41% for timed-spot specimens). Among all race-gender groups, overnight specimens had larger volumes (P < 0.01) and lower sodium (P < 0.01 to P = 0.26), potassium (P < 0.01), and chloride (P < 0.01) concentrations compared with other timed-spot urine samples, although the differences were not always significant. Urine creatinine and iodine concentrations did not differ by the timing of collection. The observed day-to-day and diurnal variations in sodium excretion illustrate the importance of accounting for these factors when developing calibration equations from this study.

Salt intake and the association with blood pressure in young Iranian children: first report from the middle East and north Africa

BACKGROUND

This study aimed to assess the salt intake of Iranian children, and to assess the correlation of urinary electrolytes excretion with blood pressure.

METHODS

This cross-sectional study was conducted in 2011-2012 among 3-10-year-old children, selected by multi-stage cluster sampling from urban and rural areas of Isfahan, Iran. The sodium (Na), potassium (K), and creatinine (Cr) were measured in a random sample of the children's first morning fasting urine. Three-day averages of dietary intakes were analyzed by the Nutritionist-4 software.

RESULTS

The mean (SD) of urinary Na was 177.17 (28.68) mEq/day without significant difference according to gender and living area. The mean (SD) dietary intakes of Na and K were 2017.76 (117.94) and 1119.06 (76.03) mg/day, respectively. Children of urban and rural areas consumed similar sources of salty foods (bread, cheese, and snacks) and had low intake of vegetables. No significant association was documented between urinary electrolytes excretions and blood pressure.

CONCLUSIONS

This study, which to the best of our knowledge is the first of its kind in the Middle East and North Africa region, revealed that Iranian young children consume a large amount of sodium and small amount of potassium. The non-significant associations of electrolyte excretions with blood pressure may be because of the very young age group of participants. Given the development of preference to salt taste from early childhood, and the tracking of risk factors of chronic diseases from this age, reducing salt intake of young children should be emphasized.

Folate catabolites in spot urine as non-invasive biomarkers of folate status during habitual intake and folic acid supplementation

BACKGROUND

Folate status, as reflected by red blood cell (RCF) and plasma folates (PF), is related to health and disease risk. Folate degradation products para-aminobenzoylglutamate (pABG) and para-acetamidobenzoylglutamate (apABG) in 24 hour urine have recently been shown to correlate with blood folate.

AIM

Since blood sampling and collection of 24 hour urine are cumbersome, we investigated whether the determination of urinary folate catabolites in fasted spot urine is a suitable non-invasive biomarker for folate status in subjects before and during folic acid supplementation.

STUDY DESIGN AND METHODS

Immediate effects of oral folic acid bolus intake on urinary folate catabolites were assessed in a short-term pre-study. In the main study we included 53 healthy men. Of these, 29 were selected for a 12 week folic acid supplementation (400 µg). Blood, 24 hour and spot urine were collected at baseline and after 6 and 12 weeks and PF, RCF, urinary apABG and pABG were determined.

RESULTS

Intake of a 400 µg folic acid bolus resulted in immediate increase of urinary catabolites. In the main study pABG and apABG concentrations in spot urine correlated well with their excretion in 24 hour urine. In healthy men consuming habitual diet, pABG showed closer correlation with PF (rs = 0.676) and RCF (rs = 0.649) than apABG (rs = 0.264, ns and 0.543). Supplementation led to significantly increased folate in plasma and red cells as well as elevated urinary folate catabolites, while only pABG correlated significantly with PF (rs = 0.574) after 12 weeks.

CONCLUSION

Quantification of folate catabolites in fasted spot urine seems suitable as a non-invasive alternative to blood or 24 hour urine analysis for evaluation of folate status in populations consuming habitual diet. In non-steady-state conditions (folic acid supplementation) correlations between folate marker (RCF, PF, urinary catabolites) decrease due to differing kinetics.

Spot urine tests in predicting 24-hour urine sodium excretion in Asian patients

OBJECTIVE

The control of hypertension is often suboptimal, and it is frequently due to excessive sodium intake. Monitoring sodium intake is cumbersome and involves 24-hour collection of urine. We hypothesize that a spot urine test can accurately predict 24-hour urine sodium excretion in an Asian population.

DESIGN

This is a prospective, observational study. We used stored urine specimens (n = 333) from the Asian Kidney Disease Study and Singapore Kidney Function Study Phase I. We measured spot urine tests and correlated these variables to the previously measured 24-hour urine sodium measurements.

RESULTS

Age, gender, ethnicity, diastolic blood pressure, height, weight, body mass index, serum creatinine, spot urine sodium, spot urine chloride, and spot urine osmolality were associated with 24-hour urine sodium excretion. The final model for predicting 24-hour urine sodium less than 100 mmol included age, gender, ethnicity, weight, and spot urine sodium.

CONCLUSION

Spot urine sodium can help monitor a patient's sodium intake when used in the derived 5-variable equation.

Correlation between sodium and potassium excretion in 24- and 12-h urine samples

Low-sodium and high-potassium diets have been recommended as an adjunct to prevention and treatment of hypertension. Analysis of these nutrients in 24-h urine has been considered the reference method to estimate daily intake of these minerals. However, 24-h urine collection is difficult in epidemiological studies, since urine must be collected and stored in job environments. Therefore, strategies for shorter durations of urine collection at home have been proposed. We have previously reported that collecting urine during a 12-h period (overnight) is more feasible and that creatinine clearance correlated strongly with that detected in 24-h samples. In the present study, we collected urine for 24 h divided into two 12-h periods (from 7:00 am to 7:00 pm and from 7:00 pm to 7:00 am next day). A sample of 109 apparently healthy volunteers aged 30 to 74 years of both genders working in a University institution was investigated. Subjects with previous myocardial infarction, stroke, renal insufficiency, and pregnant women were not included. Significant (P < 0.001) Spearman correlation coefficients (r_s) were found between the total amount of sodium and potassium excreted in the urine collected at night and in the 24-h period (r_s = 0.76 and 0.74, respectively). Additionally, the 12-h sodium and potassium excretions (means ± SD, 95% confidence interval) corresponded to 47.3 ± 11.2%, 95%CI = 45.3-49.3, and 39.3 ± 4.6%, 95%CI = 37.3-41.3, respectively, of the 24-h excretion of these ions. Therefore, these findings support the assumption that 12-h urine collected at night can be used as a reliable tool to estimate 24-h intake/excretion of sodium and potassium.

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.

Use of mean spot urine sodium concentrations to estimate daily sodium intake in patients with chronic kidney disease

OBJECTIVE

Sodium intake is an important issue for patients with chronic kidney disease (CKD). The two most widely used methods to measure sodium are 24-h urinary sodium excretion (24HUNa), which can be difficult to perform routinely, and sodium intake by dietary recall, which can be inaccurate. This study evaluated use of the mean value of three spot urinary sodium (UNa) concentrations to estimate daily sodium intake in patients with CKD.

METHODS

This cross-sectional study enrolled 305 patients with CKD, none of whom were on dialysis, who visited the nephrology clinic at the Asan Medical Center (Seoul, Korea). We performed three spot UNa tests, three calculations of the UNa/creatinine (UCr) ratio, one measurement of 24HUNa, and one measurement of sodium intake by dietary recall.

RESULTS

The 24HUNa and mean spot UNa values were significantly lower in patients with more advanced CKD (P = 0.006 and P < 0.001, respectively). One-time spot UNa was significantly higher in the evening than in the morning for patients with stage III, IV, or V CKD. Total sodium intake, but not sodium nutrient density (milligrams of sodium per 1000 kcal), was significantly different for patients with different stages of CKD (P = 0.001). The correlation coefficient between 24HUNa and mean spot UNa was 0.477 (95% confidence interval [CI] 0.384-0.562, P < 0.001), slightly higher than that between 24HUNa excretion and mean spot UNa/UCr (r = 0.313, 95% CI 0.207-0.465, P < 0.001). There was a linear relation between spot UNa and 24HUNa: mean spot UNa = 0.27 × 24HUNa + 60. Therefore, a 24HUNa excretion of 87 mEq (sodium intake 2 g/d) corresponded to a mean spot UNa level of 83 mEq/L. The correlation coefficient between sodium intake and mean spot UNa was 0.435 (95% CI 0.336-0.524, P < 0.001), significantly higher than that between sodium intake and mean spot UNa/UCr (r = 0.197, 95% CI 0.091-0.301, P = 0.001). Mean spot UNa tended to be better correlated with 24HUNa than with sodium intake.

CONCLUSION

Mean spot UNa is a simple and effective method that can be used to monitor sodium intake in patients with CKD. A daily intake of 2 g of sodium corresponds to a mean spot UNa level of approximately 83 mEq/L in patients with CKD.

Taurine in morning spot urine for the useful assessment of dietary seafood intake in Japanese children and adolescents

Background

Since our previous report on WHO CARDIAC Study data demonstrated that 24-hour urinary (24U) taurine (Tau) excretion was a useful biomarker of seafood (SF) intake and inversely related to the mortality rates of stroke and coronary heart diseases in the world, we determined that SF is important in the risk reduction of lifestyle related-diseases. The amounts of dietary SF intake are so far estimated from a nutritional survey or 24U Tau excretion.

The sodium/potassium ratio of spot urine (SU) and the 24U ratio were reported to be significantly correlated with. Therefore, we presently examined the relationship of Tau excretion in the morning SU with 24U Tau for simplifying the population comparison and the follow-up of SF intake changes in the process of food education program (FEP).

Methods

After informed consent was obtained, 54 children aged 6-11 years (Children) and 193 adolescents aged 13-18 years (Adolescents) participated in collecting precisely 24U and SU of the first urination on the same day and answered the questionnaire including age and height and weight measurements. The urine samples were measured for creatinine (Cre) and Tau, and the association of these between 24U and SU were analyzed.

Results

The success rates of 24U sampling were very high in Children and Adolescents, 96.4% and 82.4%, respectively. From the result of the multiple regression analysis of SU Tau/Cre and weight we obtained formulas for predicting 24U Tau excretion in Children and Adolescents as follows: Children: 24U Tau = 16.3 (weight) + 314.3 (SU Tau/Cre) -175.2; and Adolescents: 24U Tau = 20.2 (weight) + 644.7 (SU Tau/Cre) - 569.4.

Conclusions

The present study established the regression equation to estimate 24U Tau excretion from SU Tau/Cre and weight. These formulas are expected to contribute to the estimation of fish and SF intake and the follow-up of the change of the dietary behavior by FEP in Children and Adolescents.

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.