The role of race in determining 24-hour urine composition in white and Asian/Pacific Islander stone formers

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.

Ae index is an independent predictor of kidney stone recurrence in overweight and obese patients

BACKGROUND

Finding some convenient and economical indicators to initially screen overweight and obese patients at high risk of kidney stone recurrence can help them prevent stone recurrence with lower medical cost. The purpose of this article is to determine the clinical value of Ae index (Apo B × 1000/eGFR) as an independent predictor for kidney stone recurrence in overweight and obese populations.

METHODS

We queried the electronic medical records of patients with kidney stone operated at our hospital from March 2016 to March 2022, and selected BMI ≥ 25 kg/m2 as the study population and divided the patients into stone recurrence group and non-recurrence group. Relevant parameters of routine blood and biochemical test, glycated serum protein (GSP), and history of hypertension and hyperglycemia were collected. Then the Chi-square test, independent samples t-test or Wilcoxon rank-sum test were used to calculate the differences between the two groups of data. Next, we performed univariate and multivariate logistic regression analysis to screen out the most significant variables Apo B and eGFR, and then we calculated the Ae index using the formula Apo B × 1000/eGFR, and analyzed the relationship between Ae index and kidney stone recurrence.

RESULTS

Univariate analysis found that Apo B (OR:8.376,95%CI:3.093-22.680), Creatinine (OR:1.012,95%CI:1.003-1.021), Cystatin C(OR:2.747,95%CI:1.369-5.508), LDL-C (OR:1.588,95%CI:1.182-2.134), TC (OR:1.543,95%CI:1.198-1.988) were positively associated, eGFR (OR:0.980,95%CI:0.970-0.991) was negatively associated with kidney stone recurrence. And multivariate logistic regression analysis suggested that Apo B (OR:11.028, 95%CI:3.917-31.047) and eGFR (OR:0.976, 95%CI:0.965-0.988) were the most significant factors. Then we calculated Ae index and analyzed it, the sensitivity was 74.26% and the specificity was 60.00%, higher than either individual variable. Its smoothed curve revealed a non-linear relationship between them with the inflection point of 9.16. And the OR on the left side of the inflection point was 1.574 (95% CI: 1.228-2.018), whereas the OR on the right side of the inflection point was 1.088 (95% CI: 1.007-1.177).

CONCLUSIONS

Ae index is an easily calculated and obtained index that has some predictive value for kidney stone recurrence in overweight and obese patients, which is of interest.

Association of intestinal oxalate-degrading bacteria with recurrent calcium kidney stone formation and hyperoxaluria: a case-control study

OBJECTIVES

To investigate potential oxalate-degrading bacteria, including Oxalobacter formigenes, Lactobacillus (Lac) and Bifidobacterium (Bif) genera, and Oxalyl-CoA decarboxylase (oxc) encoding Lac (LX) and Bif (BX) species in participants with recurrent calcium kidney stones, and their correlation with 24-h urine oxalate.

PARTICIPANTS AND METHODS

Stool and 24-h urine samples were collected from 58 patients with urolithiasis (29 cases with and 29 without hyperoxaluria) and 29 healthy controls. Absolute quantitation and relative abundance of the bacteria were measured by real-time PCR. The relationship between the investigated bacteria and 24-h urine oxalate were assessed statistically.

RESULTS

The count per gram of stool and relative abundance of O. formigenes, Lac, Bif, LX and BX and the number of participants carrying O. formigenes, LX and BX bacteria were not significantly different between the groups; however, the relative abundance of O. formigenes in the kidney stone group was lower than in healthy controls (P = 0.035). More healthy controls were O. formigenes-positive compared with participants in the kidney stone group (P = 0.052). The results of the linear regression model, including all study participants, showed that the presence of O. formigenes could decrease 24-h urine oxalate (β = -8.4, P = 0.047). Neither Lac and Bif genera nor LX and BX species were correlated with calcium stones or urine oxalate.

CONCLUSION

These results emphasize the role of O. formigenes in kidney stone formation and its role in hyperoxaluria, which may be independent of kidney stone disease. Moreover, our results suggest that, although some Lac and Bif strains have oxalate-degrading potential, they may not be among the major oxalate-degrading bacteria of the gut microbiome.

Nephrolithiasis Among Middle Aged and Elderly Urban Chinese: A Report from Prospective Cohort Studies in Shanghai

INTRODUCTION

Kidney stone risk factors are understudied among Asians. Our study objective was to investigate associations of obesity and other chronic diseases with incident kidney stones among the urban Chinese.

PATIENTS AND METHODS

Included in this study are two prospective cohorts: the Shanghai Women's Health Study (N = 69,166) and Shanghai Men's Health Study (N = 58,054). Incident kidney stones were determined by self-report in 2004 and 2008. Cox regression models were used to evaluate the associations of study variables with stone risk with adjustment of demographics, medical history, and dietary intakes.

RESULTS

There were 2653 incident stones over 1,007,958 person-years of follow-up. Overall incidence rates (per 1000 person-years, 95% confidence interval [CI]) were 2.10 (1.99, 2.21) among women and 3.80 (3.59, 4.02) among men. Higher body mass index (BMI) was associated with risk (BMI ≥25 vs 18.5-24.9 kg/m², women: hazard ratio [HR] = 1.14 [95% CI 1.01, 1.28]; men: HR = 1.17 [1.03, 1.32]). High waist-hip ratio (≥0.80 and ≥0.90 for women and men, respectively) was associated with risk (HR 1.13, 95% CI 1.01, 1.27 for women; HR 1.19, 95% CI 1.05, 1.35 for men). Coronary heart disease or stroke history was associated with risk in women only (HR 1.31, 95% CI 1.10, 1.56). Hypertension history was associated with risk in men only (HR 1.27, 95% CI 1.11, 1.45). No significant association with diabetes mellitus was observed.

CONCLUSIONS

Among the Chinese, kidney stone incidence in men is almost twice that of women. Obesity is a shared risk factor. Hypertension history is associated with risk in men, whereas history of coronary heart disease or stroke is associated with risk in women.

Association of urinary citrate excretion, pH, and net gastrointestinal alkali absorption with diet, diuretic use, and blood glucose concentration

Urinary citrate (Ucit) protects against urinary stone formation. Acid base status and diet influence Ucit. However, the effect of demographics, diet, and glucose metabolism on Ucit excretion, urinary pH (U‐pH) and net gastrointestinal alkali absorption (NAA) are not known. Twenty‐four hour urine samples, blood glucose, creatinine, and cystatin C were obtained from non‐Hispanic white sibships in Rochester, MN (n = 446; 64.5 ± 9 years; 58% female). Diet was assessed by a food frequency questionnaire. The impact of blood glucose, demographics and dietary elements on Ucit excretion, U‐pH, and NAA were evaluated in bivariate and multivariable models and interaction models that included age, sex, and weight. NAA significantly associated with Ucit and U‐pH. In multivariate models Ucit increased with age, weight, eGFR_Cys, and blood glucose, but decreased with loop diuretic and thiazide use. U‐pH decreased with serum creatinine, blood glucose, and dietary protein but increased with dietary potassium. NAA was higher in males and increased with age, weight, eGFR_Cys and dietary potassium. Significant interactions were observed for Ucit excretion with age and blood glucose, weight and eGFR_Cys, and sex and thiazide use. Blood glucose had a significant and independent effect on U‐pH and also Ucit. This study provides the first evidence that blood glucose could influence urinary stone risk independent of urinary pH, potentially providing new insight into the association of obesity and urinary stone disease.

Misclassification of iodine intake level from morning spot urine samples with high iodine excretion among Inuit and non-Inuit in Greenland

Iodine nutrition is commonly assessed from iodine excretion in urine. A 24 h urine sample is ideal, but it is cumbersome and inconvenient. Hence, spot urine samples with creatinine to adjust for differences in void volume are widely used. Still, the importance of ethnicity and the timing of spot urine samples need to be settled. We, thus, collected 104 early morning spot urine samples and 24 h urine samples from Inuit and non-Inuit living in Greenland. Diet was assessed by a FFQ. Demographic data were collected from the national registry and by questionnaires. Iodine was measured using the Sandell–Kolthoff reaction, creatinine using the Jaffe method and para-amino benzoic acid by the HPLC method for the estimation of completeness of urine sampling and compensation of incomplete urine samples to 24 h excretion. A population-based recruitment was done from the capital city, a major town and a settlement (n 36/48/20). Participants were seventy-eight Inuit and twenty-six non-Inuit. The median 24 h iodine excretion was 138 (25th–75th percentile 89–225) μg/97 (25th–75th percentile 72–124) μg in Inuit/non-Inuit (P= 0·030), and 153 (25th–75th percentile 97–251) μg/102 (25th–75th percentile 73–138) μg (P= 0·026) when including compensated iodine excretion. Iodine excretion in 24 h urine samples increased with a rising intake of traditional Inuit foods (P= 0·005). Iodine excretion was lower in morning spot urine samples than in 24 h urine samples (P< 0·001). This difference was associated with iodine intake levels (P< 0·001), and was statistically significant when the iodine excretion level was above 150 μg/24 h. In conclusion, the iodine intake level was underestimated from morning spot urine samples if iodine excretion was above the recommended level.

The fluid and electrolyte balance of New Zealand European and Māori/Pacific Island athletes: An observational study

Observational research on professional athletes from the USA suggests differences may exist in sweat sodium loss based on ethnic differences. The New Zealand (NZ) sporting population is mainly of European or Māori/Pacific Island origin. Therefore, this study aimed to describe the fluid-electrolyte balance of athletes by ethnicity. A total of 20 Māori/Pacific Islanders (MP; body mass 100.97 ± 13.05 kg) and 29 NZ European (NZE; body mass 89.11 ± 11.56 kg) elite male athletes were recruited. Sweat rates were determined by body mass change during a 1-h spin cycle exercise session, during which fluid intakes and heart rate were recorded. Sweat samples were analysed for sodium concentration. Mean ± SD sweat sodium concentrations were 73.4 ± 27.2 mmol·L(-1) and 55.5 ± 26.8 mmol·L(-1) for the MP and NZE groups, respectively (p = 0.070). Sweat rate was 0.93 ± 0.26 L·h(-1) for the MP group and 0.89 ± 0.33 L·h(-1) for the NZE group (p = 0.357). Fluid intake was 1.05 ± 0.48 L and 0.93 ± 0.49 L for MP and NZE, respectively (p = 0.395). Half of the MP group gained weight during the exercise session compared to 37% of the NZE group. Pre-exercise urine specific gravity was significantly lower amongst the NZE group (1.016 ± 0.009 g mL(-1)) than the MP group (1.024 ± 0.008 g mL(-1)) p = 0.001. There was no significant difference in heart rate between the groups, p = 0.082. Hydration practices of athletes in NZ may differ by ethnicity, and this may highlight the need for more targeted education by ethnicity.

Ethnicity is important for creatinine excretion among Inuit and Caucasians in Greenland

BACKGROUND

Human nutrition, contamination and renal function are commonly assessed by the analysis of urine. A complete 24-hour urine sample is the ideal but it is inconvenient and unreliable. Thus, spot urine sampling with creatinine adjustment is widely used. Stratification for age and gender is recommended. Still, ethnicity may influence creatinine excretion.

METHODS

We collected 104 24-h urine samples among Inuit and non-Inuit living in Greenland. Completeness of sampling was checked by using para-amino benzoic acid (PABA) that also allowed for compensation of creatinine excretion when sampling was incomplete. We measured creatinine using the Jaffe method and PABA by the HPLC method.

RESULTS

Participants were recruited from the capital city, a major town and a settlement (n = 36/48/20). They were aged 30-69 years with 78 Inuit and 26 non-Inuit. Inuit were smaller than non-Inuit (Caucasians): height, 163 vs. 177 cm, p < 0.001; weight, 71 vs. 84 kg, p = 0.001 with similar BMI. Creatinine excretion was lower in Inuit compared to non-Inuit (men, 1344/1807 mg/24 h; women 894/1259 mg/24 h; p = 0.002; 0.02). It was influenced by age (p < 0.001), gender (p < 0.001), weight (p = 0.001) and ethnicity (p = 0.030) while not by the intake of the protein-rich Inuit diet in the adjusted analysis. Creatinine excretion was described by: Inuit men, 1925 mg - (13.1 × age); Inuit women, 1701 mg - (17.0 × age).

CONCLUSION

Inuit and Caucasians have different creatinine excretion. It is recommended to stratify by ethnicity in addition to adjustment for age and gender when using creatinine correction of spot urine samples.

The silicon concentration in cat urine and its relationship with other elements

To understand the effects of silicon (Si) in the urine with respect to the formation of urinary stones, the distribution of Si in urine was observed. Urine samples from cats with urolithiasis (n=10) and healthy cats (n=15) were used. The concentration of Si in the cats with urolithiasis was significantly higher (P<0.001). A significant correlation (P<0.05) was observed between the concentration of Si and those of other elements, such as calcium, magnesium, phosphorus, potassium and iron, only in the urine of the healthy cats. The distribution of elements in the urine differed between the cats with urolithiasis and the healthy cats. The Si concentration and its relationship with other elements were suggested to be useful biomarkers for urolithiasis in cats.

Differences in Urinary Stone Composition according to Body Habitus

PURPOSE

We analyzed differences in urinary stone composition according to body mass index (BMI).

MATERIALS AND METHODS

Between January 2007 and December 2010, 505 ureteral or renal stones were collected from 505 patients who underwent surgical intervention. Data on patient age, gender, BMI, urinary pH, and stone composition were collected.

RESULTS

The patients' mean age was 49.2 years (range, 20 to 83 years). Of the 505 patients, 196 (38.7%) had calcium oxalate (CO) stones, 172 (33.9%) had mixed calcium oxalate and calcium phosphate (COP) stones, 72 (14.2%) had calcium phosphate (CP) stones, 50 (9.8%) had uric acid (UA) stones, and 15 (2.9%) had struvite stones. We excluded struvite stones in the statistical analysis because of the small number of patients; a total of 490 patients were included in this study. In the multinomial logistic regression analysis, obesity was found to be associated with UA stones compared with COP stones (odds ratio [OR] 3.488; 95% confidence interval [CI] 1.732-7.025; p<0.001) and CP stones (OR 2.765; 95% CI 1.222-6.259; p=0.015). Similar results were observed for CO stones compared with COP stones (OR 2.682; 95% CI 1.727-4.164; p<0.001) and CP stones (OR 2.126; 95% CI 1.176-3.843; p<0.013).

CONCLUSIONS

Obesity was associated with UA and CO stones compared with the occurrence of COP and CP stones.

Influence of obesity on urinary pH with respect to sex in healthy Koreans

OBJECTIVES

To evaluate the association between urinary pH and metabolic risk factors, including obesity according to sex in a Korean population recruited through the health promotion center.

METHODS

From 2008 to 2010, a total of 22 297 ostensibly healthy adult Koreans who visited our health promotion center were enrolled in the present study. The relationship between urinary pH and various metabolic risk factors, including obesity, were evaluated.

RESULTS

The mean age ± SD of the study population was 45.0 ± 9.1 years. The men had a significantly greater body mass index and lower urinary pH than the women. Using multivariate logistic regression analysis, obesity significantly correlated with a lower urinary pH (≤5.5) only in men (odds ratio [OR] 1.095, P = .015) and not in women (OR 1.004, P = 0.945). Among the various factors examined, older age (>45 years), greater fasting blood glucose, and hyperuricemia were factors significantly associated with a lower urinary pH in both groups. Hypertriglyceridemia was a significant factor associated with lower urinary pH only in men, and a lower high-density lipoprotein cholesterol was the significant factor for a lower urinary pH in women.

CONCLUSIONS

The results of the present study revealed that obesity is significantly correlated with lower urinary pH (≤5.5) only in men.

Dietary therapy for patients with hypocitraturic nephrolithiasis

Citrate is an inhibitor of urinary stone formation. Clinical and in vitro data suggest that increasing urine citrate levels will decrease the precipitation of calcium stones. Historically, low urinary citrate has been treated with oral potassium citrate or sodium citrate supplementation, but recent studies have shown the potential of dietary interventions to raise urine citrate levels. Dietary therapy with commercial or homemade beverages is attractive to patients who would prefer nonpharmacological intervention. To date, several drinks have shown promise but no single beverage has been found to consistently raise urine citrate levels in a reproducible fashion. Further research is necessary to develop the ideal dietary therapy for hypocitraturic calcium nephrolithiasis.