Addressing the problem of inaccuracy of measured 24-hour urine collections due to incomplete collection

A dilute and shoot method for urinary free cortisol analysis by LC-MS/MS

24-hour urinary free cortisol (UFC) is considered as the first-line test for screening and diagnosis of Cushing's syndrome. Although 24-hour UFC assay has been extensively studied by liquid chromatography-tandem mass spectrometry (LC-MS/MS), an accurate assay coupled with a reliable sample preparation procedure and a method-specific reference interval would be very important for reasonable diagnosis. In this study, a simple dilute and shoot method has been proposed for UFC determination by LC-MS/MS. Namely, 50 µL of urine sample was mixed with 200 µL of a 50 % methanol/water solution containing the internal standard cortisol-13C3. The mixture was centrifuged and the supernatant was used for direct analysis by LC-MS/MS. This method was validated with wide linear range from 0.625 to 500 ng/ml with coefficients of variation (CVs) ≤ 3.64 %, excellent precision (intra-day CVs ≤ 5.70 % and inter-day CVs ≤ 5.33 %) and good recovery in the range of 93.3-109 %. The preservatives were further evaluated for urine storage. It was recommended that no preservatives could be used in collection of 24-hour urine for good detecting peaks. The investigation of reference interval and diagnostic performance finally confirmed the potential usage of this LC-MS/MS assay in routing clinical testing.

Meta-analysis guided development of a standard artificial urine

In this study, we present the first meta-analysis of human urine reported in the literature, drawing data from a total of 35 articles with a combined participant count of 14,021. Through this analysis, we have developed an artificial urine (AU) composition that can be adjusted within typical physiological parameters for in vitro applications. Our findings demonstrate the utility of this AU in determining the solubility of nitrofurantoin, particularly in the context of crystalluria. Notably, we observe that in saline, nitrofurantoin solubility, within the framework of its urinary pharmacokinetics, suggests a risk of crystalluria. However, in AU, this risk is mitigated due to complexation with urea. More broadly, we anticipate that our developed formulation will serve as a foundation for translational studies across biomedical and pharmaceutical sciences.

High dietary salt intake attenuates nitric oxide mediated endothelium-dependent vasodilation and increases oxidative stress in pregnancy

OBJECTIVE

This study aimed to investigate the impact of dietary salt intake during normal pregnancy on maternal microvascular and macrovascular endothelium-dependent reactivity and oxidative stress level.

MATERIALS AND METHODS

In this cross-sectional study, based on their 24-h urinary sodium excretion, pregnant women (37-40 weeks of gestation) were divided into three groups: normal salt (<5.75 g/day, N  = 12), high salt (5.75-10.25 g/day, N  = 36), and very high salt (VHS;>10.25 g/day, N  = 17). Forearm skin microvascular reactivity in response to vascular occlusion, local heating (LTH) and iontophoresis of acetylcholine (AChID), as well as brachial artery flow mediated dilation (FMD) were measured. Serum nitric oxide, endocan, 8-iso-prostaglandin F2α (8-iso-PGF2α), thiobarbituric acid reactive substances (TBARS), and ferric-reducing ability of plasma assay were measured as biomarkers of endothelial function/activation and oxidative stress.

RESULTS

Brachial artery FMD, microvascular AChID, and LTH were significantly decreased in VHS compared with NS group, while LTH was also decreased in normal salt compared with high salt group. Nitric oxide was significantly decreased in both high salt and VHS groups compared with normal salt. Endocan, 8-iso-PGF2α, and TBARS were significantly increased in VHS compared with the normal salt group.

CONCLUSION

High dietary salt intake is associated with decreased nitric oxide mediated endothelium-dependent vasodilation in peripheral microcirculation and macrocirculation of healthy pregnant women due to increased oxidative stress.

Urine Albumin Measurements in Clinical Diagnostics

BACKGROUND

Measurement of urine albumin is critical for diagnosis, risk classification, and monitoring of chronic kidney disease (CKD). Guidelines recommend clinical decision cutoffs for the urine albumin-to-creatinine ratio (ACR) of 30 and 300 mg/g (3 and 30 mg/mmol). However, differences among manufacturers' routine urine albumin measurement procedures have been found to exceed 40%, suggesting CKD diagnosis and risk classification may vary depending upon the specific measurement procedure implemented in the laboratory.

CONTENT

This review discusses urine albumin pathophysiology and clinical practice guideline recommendations for CKD. The review also provides recommendations for urine specimen collection and storage, and results reporting for the ACR. Recent advances in measurement techniques and development of reference systems intended to facilitate standardization of urine albumin measurements are reviewed.

SUMMARY

Urine albumin is an important measurement procedure used for diagnosis, risk classification, and management of CKD. Urine albumin results should be reported as the ACR using quantitative measurement procedures. Random urine collections used for albuminuria screening should be followed by confirmation with first morning void collections to reduce variation and increase diagnostic accuracy for urine albumin measurement. Most measurement procedures utilize immunoturbidimetric or immunonephelometric techniques. However, results vary significantly among measurement procedures, potentially resulting in differences in classification or risk assessment for CKD. The National Institute for Standards and Technology (NIST) and other laboratories are developing reference systems, including liquid chromatography-tandem mass spectrometry candidate reference measurement procedures and reference materials, to enable standardization of routine measurement procedures.

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

OBJECTIVE

To determine the appropriateness of three widely used formulas estimating 24-h urinary Na (24hUNa) from spot urine samples in the Chinese population.

DESIGN

Systematic review and meta-analysis.

SETTING

Literature review was conducted to identify studies for estimating 24hUNa using the Kawasaki, Tanaka and INTERSALT formulas simultaneously in PubMed, Embase and the Cochrane library databases. The mean difference (MD) and correlation coefficients (r) between measures and estimates from different formulas were assessed.

PARTICIPANTS

Information extraction and quality assessment were performed in thirteen studies involving 8369 subjects.

RESULTS

Two studies which affected the overall robustness were excluded in the 'leave-one-out' sensitivity analyses. Within the final meta-analysis included eleven studies and 7197 participants, 36·07 mmol/d (95 %CI 16·89, 55·25) of MD was observed in the Kawasaki formula, and -19·62 mmol/d (95 %CI -37·37, -1·87) in the Tanaka formula and -35·78 mmol/d (95 %CI -50·76, -20·80) in the INTERSALT formula; a pooled r-Fisher's Z of 0·39 (95 %CI 0·32, 0·45) in the Kawasaki formula, 0·43 (95 %CI 0·37, 0·49) in the Tanaka formula and 0·36 (95 %CI 0·31, 0·42) in the INTERSALT formula. Subgroup analyses were conducted to explore the possible factors affecting the accuracy of the formula estimation from three mainly aspects: population types, Na intake levels and urine specimen types.

CONCLUSIONS

The meta-analysis suggested that the Tanaka formula performed a more accurate estimate in Chinese population. Time of collecting spot urine specimens and Na intake level of the sample population might be the main factors affecting the accuracy of the formula estimation.

Intraindividual variations of urinary biomarkers in hospitalized children with glomerular diseases: a prospective observational study

This study aimed to assess the intraindividual variations of urinary biomarkers in hospitalized children with glomerular diseases. Hospitalized children with glomerular diseases participated in the study. For each patient, an overnight (9:00 p.m.-7:00 a.m.) urine was collected, followed by a 24-h urine (classified into four distinct periods: morning 7:00 a.m.-12:00 p.m., afternoon 12:00 p.m.-4:00 p.m., evening 4:00 p.m.-9:00 p.m., and overnight 9:00 p.m.-7:00 a.m.). The concentrations of protein, albumin, N-acetyl-beta-D-glucosaminidase, and epidermal growth factor (EGF) were measured and normalized by three correction factors (creatinine, osmolality, or specific gravity, respectively). Additionally, the 2nd overnight urine sample was grouped into different aliquots according to centrifugation, additives, storage temperature, or delayed processing. Twenty (14 boys, 6 girls) children were enrolled, with an average age of 11.3 years. Among the three correction factors, creatinine-normalized biomarkers provided the best agreements among different periods over 24 h. There were significant diurnal variations during 24 h in the concentrations of urinary protein, albumin, N-acetyl-beta-D-glucosaminidase, and EGF (p = 0.001, p = 0.003, p = 0.003, and p = 0.003, respectively). Evening urine overestimated 24-h urinary protein and albumin, while overnight urine underestimated 24-h urinary albumin. Urinary EGF showed low variability within a day or between the 2 days (coefficients of variation 10.2% and 10.6%, respectively) and excellent agreements (intraclass correlation coefficients > 0.9) with 24-h urinary concentration. Furthermore, urinary EGF was not affected by centrifugation, additives, storage temperature, or delayed processing of urine samples (all p > 0.05).  Conclusion: Given the diurnal variations of urinary biomarkers, urine samples should be collected during the same time period in clinical practice if possible. The results also extend the evidence for urinary EGF as a relatively stable biomarker applied in the future clinical practice. What is Known: • Urinary biomarkers have been widely used or discussed in making diagnoses and therapy regimens and estimating the prognosis of pediatric glomerular diseases. It remains unclear whether their levels would be affected by the time of sample collection, processing methods, and storage conditions in hospitalized children with glomerular diseases. What is New: • The levels of both commonly used biomarkers and novel biomarkers exhibited diurnal variations in hospitalized children with glomerular diseases. • Our results extend the evidence for urinary EGF as a relatively stable biomarker applied in the future clinical practice.

A systematic review and meta-analysis of urinary biomarkers in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

BACKGROUND

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a multifactorial illness that affects many body systems including the immune, nervous, endocrine, cardiovascular, and urinary systems. There is currently no universal diagnostic marker or targeted treatment for ME/CFS. Urine is a non-invasive sample that provides biomarkers that may have the potential to be used in a diagnostic capacity for ME/CFS. While there are several studies investigating urine-based biomarkers for ME/CFS, there are no published systematic reviews to summarise existing evidence of these markers. The aim of this systematic review was to compile and appraise literature on urinary-based biomarkers in ME/CFS patients compared with healthy controls.

METHODS

Three databases: Embase, PubMed, and Scopus were searched for articles pertaining to urinary biomarkers for ME/CFS compared with healthy controls published between December 1994 to December 2022. The final articles included in this review were determined through application of specific inclusion and exclusion criteria. Quality and bias was assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Case Control Studies. A meta-analysis according to Cochrane guidelines was conducted on select studies, in particular, those that investigate urinary free cortisol levels in ME/CFS patients compared to healthy controls using the program STATA 17.

RESULTS

Twenty-one studies were included in this review. All of the studies investigated urinary-based markers in ME/CFS patients compared with healthy controls. The reported changes in urinary outputs include urinary free cortisol (38.10%), carnitine (28.6%), iodine (4.76%), and the metabolome (42.86%). In most cases, there was minimal overlap in the main outcomes measured across the studies, however, differences in urinary free cortisol between ME/CFS patients and healthy controls were commonly reported. Seven studies investigating urinary free cortisol were included in the meta-analysis. While there were significant differences found in urinary free cortisol levels in ME/CFS patients, there was also substantial heterogeneity across the included studies that makes drawing conclusions difficult.

CONCLUSIONS

There is limited evidence suggesting a consistent and specific potential urinary-based biomarker for ME/CFS. Further investigations using more standardised methodologies and more stringent case criteria may be able to identify pathophysiological differences with diagnostic potential in ME/CFS patients compared with healthy controls.

Effect of cognitive processing therapy on markers of cardiovascular risk in posttraumatic stress disorder patients: A randomized clinical trial

OBJECTIVE

Posttraumatic stress disorder (PTSD) is associated with elevated risk of coronary heart disease (CHD); however, the effects of PTSD treatment on CHD biomarkers is unknown. This study examined whether cognitive processing therapy (CPT) improves 24-hourheart rate variability (HRV), a predictor of CHD mortality.

METHODS

Individuals between the ages of 40 and 65 years with PTSD (n = 112) were randomized to receive 12 sessions of CPT or a Waiting List (WL) intervention comprised of 6 weekly telephone checks of emotional status. The primary outcome variable was 24-hour HRV estimated from the standard deviation of all normal R-R intervals (SDNN); secondary outcomes were the root mean square of successive differences between heart beats (RMSSD), low-frequency HRV (LF-HRV) and high-frequency HRV (HF-HRV). Secondary outcomes also included 24-hour urinary catecholamine excretion, plasma C-reactive protein (CRP), and flow-mediated dilation (FMD) of the brachial artery. For outcomes, linear mixed longitudinal models were used to estimate mean differences (Mdiff).

RESULTS

Participants randomized to the CPT group did not show improved SDNN (M_diff = 9.8; 95%CI, -2.7 to 22.3; p = 0.12), the primary outcome variable, but showed improved RMSSD (M_diff = 3.8; 95% CI, 0.5 to 7.1; p = 0.02), LF- HRV (Mdiff =0.3; 95% CI, 0.1 to 0.5; p = 0.01), and HF-HRV (M_diff = 0.3; 95% CI, 0.0 to 0.6; p = 0.03) compared to WL. There were no differences between groups in catecholamine excretion, FMD, or inflammatory markers.

CONCLUSION

Treating PTSD may not only improve quality of life but may also help ameliorate heightened CHD risk characteristics of PTSD.

Simplified urinary steroid profiling by LC-MS as diagnostic tool for malignancy in adrenocortical tumors

OBJECTIVES

Preoperative identification of malignant adrenal tumors is challenging. 24-h urinary steroid profiling by LC-MS/MS and machine learning has demonstrated high diagnostic power, but the unavailability of bioinformatic models for public use has limited its routine application. We here aimed to increase usability with a novel classification model for the differentiation of adrenocortical adenoma(ACA) and adrenocortical carcinoma(ACC).

METHODS

Eleven steroids (5-pregnenetriol, dehydroepiandrosterone, cortisone, cortisol, α-cortolone, tetrahydro-11-deoxycortisol, etiocholanolone, pregnenolone, pregnanetriol, pregnanediol, and 5-pregnenediol) were quantified by LC-MS/MS in 24-h urine samples from 352 patients with adrenal tumor (281 ACA,71 ACC). Random forest modelling and decision tree algorithms were applied in training (n=188) and test sets (n=80) and independently validated in 84 patients with paired 24-h and spot urine.

RESULTS

After examining different models, a decision tree using excretions of only 5-pregnenetriol and tetrahydro-11-deoxycortisol classified three groups with low, intermediate, and high risk for malignancy. 148/217 ACA were classified as being at low, 67 intermediate, and 2 high risk of malignancy. Conversely, none of the ACC demonstrated a low-risk profile leading to a negative predictive value of 100% for malignancy. In the independent validation cohort, the negative predictive value was again 100% in both 24-h urine and spot urine with a positive predictive value of 87.5% and 86.7%, respectively.

CONCLUSIONS

This simplified LC-MS/MS-based classification model using 24-h-urine provided excellent results for exclusion of ACC and can help to avoid unnecessary surgeries. Analysis of spot urine led to similarly satisfactory results suggesting that cumbersome 24-h urine collection might be dispensable after future validation.

Association of 24-h urinary sodium excretion with microalbuminuria in a Chinese population

To assess the relationship of sodium, potassium and the ratio of sodium to potassium (Na/K) with albuminuria, a cross-sectional study was carried out in China in 2017. Sodium, potassium and albumin excretions were examined in a 24-h (h) urine sample collected from 1486 participants. Microalbuminuria was defined as 24-h urinary albumin excretion between 30 and 300 mg/24 h. The participants had an average age of 46.2 ± 14.1 years old, and 48.9% were men. The proportion of patients with microalbuminuria was 9.0%. As illustrated by the adjusted generalized linear mixed model, sodium concentration increased significantly with the increase in 24-h urinary albumin (β = 1.16, 95% confidence interval (CI) 0.38-1.93; P = 0.003). Multivariable-adjusted logistic regression analyses demonstrated that the odds ratio (OR) of microalbuminuria increased with the quartiles of sodium [OR = 2.20, 95% CI 1.26-3.84 (the maximum quartile vs. the minimum quartile), P_{for trend} = 0.006]. Potassium and the Na/K ratio did not have any association with outcome indicators. A high amount of sodium intake was potentially correlated with early renal function impairment.

The Potential of Self-Assessment and Associated Factors for Delayed Symptomatic Hyponatremia Following Transsphenoidal Surgery: A Single Center Experience

(1) Background: We identified screening parameters and associated factors for delayed, symptomatic hyponatremia (DSH) following inpatient discharge after transsphenoidal surgery (TSS). (2) Methods: In this prospective, monocentric study, 108 patients who underwent TSS for pituitary pathologies were included, provided with a questionnaire and instructed to document urine specific gravity, fluid intake/urine output, body weight and clinical symptoms for every of five days following discharge from hospital. (3) Results: The overall incidence of DSH within 14 days following discharge from the hospital was 14.8% (n = 9). Symptomatic patients presented on average 8.6 days after surgery. Mild DSH was present in 3.3% of the patients, moderate in 1.6% and severe hyponatremia in 9.8% of patients. Female sex (p = 0.02) and lower BMI (p = 0.02), as well as nausea (66.7%; p < 0.01) and emesis (33.3%; p < 0.05), were associated with DSH. A significant weight delta between morning and afternoon weight two days before the event of DSH between both groups (1.26 kg (n = 5) vs. 0.79 kg (n = 52), p < 0.05) was detected. (4) Conclusions: Handing out a symptom questionnaire at discharge seems to be an easy and feasible tool for the detection of DSH after hospital discharge.

Impact of Paraben Exposure on Adiposity-Related Measures: An Updated Literature Review of Population-Based Studies

Parabens are alkyl esters of p-hydroxybenzoic acid that are commonly used in pharmaceutical and cosmetic products. Humans are exposed to parabens when they use these products and through diet. There are growing concerns that paraben exposure can adversely impact human health. The endocrine-disrupting and obesogenic properties of parabens have been observed in animal studies and in vitro, prompting the increase in population-based studies of paraben exposure and adiposity-related endpoints. In this review, we summarize epidemiological studies published between 2017 and 2022 that examined paraben exposure in utero, between birth and adolescence, and in adulthood, in relation to adiposity-related measures. Overall, these studies provide some evidence that suggests that paraben exposure, especially during critical development windows, is associated with adiposity-related measures. However, we have noted several limitations in these studies, including the predominance of cross-sectional studies, inconsistent sample collection procedures, and small sample sizes, which should be addressed in future studies.

The association of knowledge, attitudes and behaviors related to salt with 24-h urinary sodium, potassium excretion and hypertensive status

To understand the association between sodium and potassium consumption levels, hypertension and knowledge, attitudes and behaviors (KAB) toward salt and the commitment to effective sodium reduction and potassium supplementation to achieve the purpose of suppressing hypertension. A stratified multistage random sampling method was used to obtain a representative provincial sample of 7512 residents aged 18-69 years through a cross-sectional survey by the Salt Reduction and Hypertension Prevention Project (SRHPP) in Zhejiang Province of China in 2017-2018. A screening including demographic, anthropometric, salt-related KAB and physical measurements was implemented, and 24-h urine of approximately 1/5 of the participants was collected and tested. The mean age was 44.8 years, 50.1% were women, 44.0% lived in urban areas, and hypertension or prehypertension accounted for approximately 35.0%. The mean 24-h urinary sodium and potassium excretion were 3848.5 (1661.1) mg/d and 1491.1 (710.9) mg/d, respectively. KAB in urban areas was generally more favorable than in rural areas, women were better than men, and the optimal blood pressure group was better than the other two groups (P < 0.05). However, the awareness and correct use rate of salt-restricted spoons, low-sodium salt and nutrition labeling were lower. A multivariable linear regression model indicated that KAB had a smaller effect on sodium (two indicators effective for promoting sodium reduction) and a greater effect on potassium (six indicators effective for promoting potassium supplementation) and mainly focused on knowledge and behavior indicators. A multivariable logistic regression model indicated that mastering more knowledge and taking active measures could effectively reduce the transition to hypertension, even if the individual was already in prehypertension. There is much room for improvement of salt-related KAB in the Chinese population. A clear association indicates that KAB can help to reduce sodium and supplement potassium, especially potassium, and help to suppress the development of hypertension. The role of beliefs in KAB should be fully valued and improved, similar to knowledge and behaviors. This study provides important evidence and insight into China's efforts to meet the targets of salt reduction and hypertension prevention.

24-hour sodium and potassium excretion in the Americas: a systematic review and meta-analysis

Objective

To determine the 24-hour urinary sodium and potassium excretions in the Americas.

Methods

A systematic review and meta-analysis were performed seeking for studies conducted between 1990 and 2021 in adults living in any sovereign state of the Americas in Medline, Embase, Scopus, SciELO, and Lilacs. The search was first run on October 26^th, 2020 and was updated on December 15^th, 2021. Of 3 941 abstracts reviewed, 74 studies were included from 14 countries, 72 studies reporting urinary sodium (27 387 adults), and 42 studies reporting urinary potassium (19 610 adults) carried out between 1990 and 2020. Data were pooled using a random-effects meta-analysis model.

Results

Mean excretion was 157.29 mmol/24h (95% CI, 151.42-163.16) for sodium and 57.69 mmol/24h (95% CI, 53.35-62.03) for potassium. When only women were considered, mean excretion was 135.81 mmol/24h (95% CI, 130.37-141.25) for sodium and 51.73 mmol/24h (95% CI, 48.77-54.70) for potassium. In men, mean excretion was 169.39 mmol/24h (95% CI, 162.14-176.64) for sodium and 62.67 mmol/24h (95% CI, 55.41-69.93) for potassium. Mean sodium excretion was 150.09 mmol/24h (95% CI, 137.87-162.30) in the 1990s and 159.79 mmol/24h (95% CI, 151.63-167.95) in the 2010s. Mean potassium excretion was 58.64 mmol/24h (95% CI, 52.73-64.55) in the 1990s and 56.33 mmol/24/h (95% CI, 48.65-64.00) in the 2010s.

Conclusions

These findings suggest that sodium excretions are almost double the maximum level recommended by the World Health Organization and potassium excretions are 35% lower than the minimum requirement; therefore, major efforts to reduce sodium and to increase potassium intakes should be implemented.

Validity of predictive equations for 24-h urinary sodium excretion at the population and individual levels among Chinese adults aged 18-69 years

Spot urine (SU) collection is a convenient method commonly used for sodium estimation, but its validity in predicting 24-h urinary sodium (24-hUNa) excretion has not been thoroughly evaluated among the general population. The aim of this study was to comprehensively assess the validity of eight existing methods in predicting 24-hUNa excretion by using SU samples among Chinese adults. We analyzed 1424 representative individuals aged 18 to 69 years. We compared the measured and estimated measurements of 24-hUNa at the population level by examining bias, the correlation, intraclass correlation coefficients (ICCs), receiver operating characteristic (ROC) curves and Bland–Altman plots and analyzed the relative and absolute differences and misclassification at the individual level. The bias for all methods was significant (all p < 0.001), among which the smallest bias was − 7.9 mmol for the Toft formula and the largest bias was − 53.8 mmol for the Mage formula. Correlation coefficients were all less than 0.380, all formulas exhibited an area under the ROC curve below 0.683, and the Bland–Altman plots indicated slightly high dispersion of the estimation biases at higher sodium levels regardless of the formula. The proportions of relative differences > 40% for the eight methods were all over one-third, the proportions of absolute differences > 51.3 mmol/24 h (3 g/day NaCl) were all over 40%, and the misclassification rates (7, 10, and 13 g/day NaCl as cutoff points) were all over 65%. Caution remains due to poor validity between estimated and actual measurements when using the eight formulas to obtain a plausible estimation for surveillance of the Chinese population sodium excretion, and the results do not support the application of SU to estimate sodium intake at the individual level due to its poor performance with respect to classification.

Development of a Method for Estimating Dietary Salt Intake Using the Overnight Urinary Sodium/Potassium Ratio

Background

There are many patients who need to restrict and assess salt in their diet. However, it is difficult to estimate daily salt intake accurately and easily. Therefore, a method for estimating dietary salt intake using the overnight urinary sodium (Na)/potassium (K) ratio was developed.

Methods

The study involved 43 healthy adults (13 males, 30 females). From 2018 to 2020, subjects consumed a salt-adjusted diet for 11 - 30 days continuously, and overnight urine was collected daily. Using the previous day's salt intake as the objective variable, an equation for estimating the salt intake was developed using a general linear model. To verify the accuracy of the estimating equation, the estimated salt intake of the previous day was calculated using our equation and Tanaka's equation, which is an estimating equation from spot urine widely used in clinical practice and epidemiological studies to estimate dietary salt intake, and they were compared with the actual salt intake.

Results

The results of the analysis showed that model 1 (previous day's salt intake (g) = 3.62 + 0.64 × urinary Na/K ratio + 0.18 × conductivity (mS/cm) - 0.43 × sex (male 0, female 1)) was the optimal model. Then, salt intake was estimated using model 1 and Tanaka's equation, and compared with actual salt intake. The Pearson's product-moment correlation coefficient between the actual and estimated salt intake was r = 0.618 (P < 0.001) and r = 0.573 (P < 0.001) for model 1 estimates and Tanaka's equation estimates, respectively. The percentages of errors within ±30% from the actual salt intake were 64.2% and 58.4% for model 1 and Tanaka's equation, respectively.

Conclusion

An equation for estimating salt intake was developed using the Na/K ratio and conductivity of overnight urine. Although the applicability of this method to hypertensive patients and the elderly has not been studied and needs to be clarified in the future, the estimating equation developed is simple and may be a useful method for daily monitoring of dietary salt intake.

Improving Compliance with 24-H Urine Collections: Understanding Inadequacies in the Collection Process and Risk Factors for Poor Compliance

PURPOSE OF REVIEW

The purpose of this review paper is to describe the 24-h urine collection in terms of its utility, collection process, and common problems with its acquisition.

RECENT FINDINGS

Although 24-h urine collections are standard of care for high-risk stone formers, several nuances in test acquisition including inaccurate urine collections 50% of the time and poor patient compliance limit its potential utility. Compliance in obtaining 24-h urine collections has been shown to be improved in patients who have not undergone surgical treatment of urinary calculi, patients with metabolic stone disease or family history of stone disease, Caucasian ethnicity, and in those with more sedentary occupations. Studies show conflicting data of compliance regarding patient age and gender. Physicians must understand the difficulties regarding 24-h urine collections including patient compliance, variability between collections, and complexities with interpretation to best utilize this tool in guiding clinical management for the treatment of nephrolithiasis.

Use of Salt-Restriction Spoons and Its Associations with Urinary Sodium and Potassium in the Zhejiang Province of China: Results of a Population-Based Survey

In China, a major source of sodium is salt added during cooking. In this context, use of a salt-restriction spoon (SRS) has been promoted in public health campaigns and by health care providers. To describe use of and factors associated with SRS use, knowledge of correct use, and actual correct use. This study is a population-based, representative survey of 7512 residents, aged 18 to 69 years, of China’s Zhejiang Province. The survey, which was conducted in 2017 using a multistage random sampling strategy, collected demographic information, SRS use, and physical measurements; a 24-h urine collection was obtained from 1,496 of the participants. The mean age of the participants was 44.8 years, 50.1% were females, and over 1/3 (35.3%) were classified as hypertensive. Mean 24-h urinary sodium and potassium excretions were 167.3(72.2) mmol/24 h and 38.2(18.2) mmol/24 h, respectively. Only 12.0% (899/7512) of participants once used or were currently using SRS; of the 899 users, 73.4% knew how to use the SRS correctly, and just 46.5% actually used it correctly. SRS use was more commonly associated with behavioral factors rather than socio-demographic factors. Initiation of SRS use by health care providers was associated with correct technical knowledge of SRS. Lower sodium-to-potassium ratio was associated with SRS use, while SRS use was not associated with urinary sodium and potassium excretion. Use of SRS was uncommon in Zhejiang Province of China. Given that a common source of sodium in China is salt added during cooking, use of SRS is an appealing strategy, ideally as part of a multi-component campaign.

Association between 24-h urinary sodium and potassium excretion and blood pressure among Chinese adults aged 18-69 years

The direction and magnitude of the association between sodium and potassium excretion and blood pressure (BP) may differ depending on the characteristics of the study participant or the intake assessment method. Our objective was to assess the relationship between BP, hypertension and 24-h urinary sodium and potassium excretion among Chinese adults. A total of 1424 provincially representative Chinese residents aged 18 to 69 years participated in a cross-sectional survey in 2017 that included demographic data, physical measurements and 24-h urine collection. In this study, the average 24-h urinary sodium and potassium excretion and sodium-to-potassium ratio were 3811.4 mg/day, 1449.3 mg/day, and 4.9, respectively. After multivariable adjustment, each 1000 mg difference in 24-h urinary sodium excretion was significantly associated with systolic BP (0.64 mm Hg; 95% confidence interval [CI] 0.05-1.24) and diastolic BP (0.45 mm Hg; 95% CI 0.08-0.81), and each 1000 mg difference in 24-h urinary potassium excretion was inversely associated with systolic BP (- 3.07 mm Hg; 95% CI - 4.57 to - 1.57) and diastolic BP (- 0.94 mm Hg; 95% CI - 1.87 to - 0.02). The sodium-to-potassium ratio was significantly associated with systolic BP (0.78 mm Hg; 95% CI 0.42-1.13) and diastolic BP (0.31 mm Hg; 95% CI 0.10-0.53) per 1-unit increase. These associations were mainly driven by the hypertensive group. Those with a sodium intake above about 4900 mg/24 h or with a potassium intake below about 1000 mg/24 h had a higher risk of hypertension. At higher but not lower levels of 24-h urinary sodium excretion, potassium can better blunt the sodium-BP relationship. The adjusted odds ratios (ORs) of hypertension in the highest quartile compared with the lowest quartile of excretion were 0.54 (95% CI 0.35-0.84) for potassium and 1.71 (95% CI 1.16-2.51) for the sodium-to-potassium ratio, while the corresponding OR for sodium was not significant (OR, 1.28; 95% CI 0.83-1.98). Our results showed that the sodium intake was significantly associated with BP among hypertensive patients and the inverse association between potassium intake and BP was stronger and involved a larger fraction of the population, especially those with a potassium intake below 1000 mg/24 h should probably increase their potassium intake.

False elevations in urinary metanephrines: under-recognised pitfall with 24-hour urinary volume collection

One pitfall in 24-hour urine collection is the input of incorrect urinary volume by the reference laboratory. This may lead to an incorrect diagnosis of pheochromocytoma or paraganglioma. A 48-year-old African-American woman was seen in the clinic for an elevated 24-hour urine metanephrine screen during workup for secondary hypertension. Urine volume was found to be incorrectly inputted by the lab as 9750 mL rather than 975 mL. The urinary metanephrines were then recalculated and the 24-hour urinary metanephrines resulted within normal limits. This case highlights this unique and potentially under-recognised error in testing with 24-hour urine volume collection.