Urinary protein excretion in healthy children

The urinary total protein excretion was determined in 270, 18-24 hr urine samples from 130 healthy children of different age groups using the tannic acid-Fe3+-method of Yatzidis [1977]. The daily protein excretion of premature infants in the first month of life varies between 14-60 mg, with a mean of 29 mg, and that of fullterm newborn infants between 15-68 mg, with a mean of 32 mg. Protein excretion increases with age and amounts to 29-238 mg (mean 83 mg) in 10-16 year old children. Thus, the urinary protein concentration during the neonatal period is high when compared to adult values. This explains the "trace" and "positive" reactions frequently obtained in this period of life with Albustix. In 92 urine samples proteins were fractionated by sodium dodecyl sulphate gel discelectrophoresis. Hemoglobinuria was found during the first weeks of life and tubular type proteinuria was found in newborns and infants. The present data suggest that the proteinuria is due to ineffective proximal tubular reabsorption of low molecular weight microproteins as a result of glomerulo-tubular imblance in early life.     

Urinary calcium excretion in healthy Thai children

The objective of this study was to determine age-specific reference values for urinary calcium/creatinine ratios (UCa/Cr) of children in southern Thailand. Non-fasting urine samples were collected from a random population of 488 healthy children (282 males, 206 females) ranging in age from 17 days to 15 years. Samples were divided into six groups by age. Subjects whose calcium levels exceeded the 95th percentile within each age group were classified as having hypercalciuria. Pyuria, hematuria, proteinuria, urinary sodium, and potassium levels in children with normal UCa/Cr were compared with levels in children with high UCa/Cr. The 95th percentiles for UCa/Cr (mg/mg) by age were: <6 months, 0.75; 6 months to <12 months, 0.64; 12 months to <2 years, 0.40; 2 years to <5 years, 0.38; 5 years to <10 years, 0.29; and 10 years to <15 years, 0.26. Pyuria, hematuria, and proteinuria were no more prevalent in the 22 children with hypercalciuria than in children with normal urinary calcium levels. Urinary sodium/creatinine ratios (UNa/Cr) and urinary sodium/potassium ratios (UNa/K) were correlated with UCa/Cr (r=0.41, P<0.0001 and r=0.24, P<0.0001, respectively). Urinary potassium/creatinine ratios (UK/Cr) were not (r=0.05, P>0.1)). Children with high UCa/Cr ratios also had higher UNa/Cr and UNa/K (5.6±7.1 vs. 2.6±1.5, P<0.001 and 5.4±2.3 vs. 2.5±0.23, P<0.05, respectively) The study established reference values for random, non-fasting UCa/Cr for healthy Thai children and indicated that urinalysis is not a good indicator of hypercalciuria. Received: 30 April 1999 / Revised: 19 August 1999 / Accepted: 19 August 1999     

Urinary mineral excretion in healthy Iranian children

The purpose of this study was to determine normal reference values for urinary calcium/creatinine (Ca/Cr), phosphate/creatinine (P/Cr), magnesium/creatinine (Mg/Cr), sodium/creatinine (Na/Cr), potassium/creatinine (K/Cr), sodium/potassium (Na/K), calcium/sodium (Ca/Na), and uric acid/creatinine ratios in healthy Iranian children. Nine hundred and ninety children (515 boys, 475 girls) aged 1 month to 14 years were studied. Two non-fasting random urine specimens (1 week apart) from each subject and 24-h urine collections from 114 children were analyzed for Ca, P, Mg, uric acid, Na, K, and Cr. Urinary Ca/Cr, P/Cr, Mg/Cr, Na/Cr, K/Cr, Na/K, Ca/Na, and uric acid/creatinine ratios were determined from each sample. Non-fasting Ca/Cr, P/Cr, Na/Cr, K/Cr, Na/K, Ca/Na, and uric acid/creatinine ratios were not significantly different between the sexes (P>0.05). Urinary Mg/Cr ratios were higher in girls than boys (P<0.001). No significant relationships were found between urinary Ca/Cr and urinary Na/Cr, urinary Ca/Cr and urinary Na/K, and urinary Ca/Cr and urinary Ca/Na (P>0.05). The P/Cr values showed a gradual decrease with age (from mean+/-SD 0.962+/-0.172 mg/mg at 1 month of life to 0.318+/-0.124 mg/mg at 14 years) (P<0.05). The Ca/Cr ratio was highest between 6 months and 3 years (mean+/-SD=0.047+/-0.041 mg/mg). Following a moderate decrease it stabilized by the age of 7 years (mean+/-SD=0.038+/-0.044 mg/mg). Urinary ratios of Mg/Cr were significantly higher in children under 10 years (mean+/-SD=0.042+/-0.015 mg/mg) compared with the 11- to 14-year age group (mean+/-SD=0.031+/-0.001 mg/mg) (P<0.05). The uric acid/creatinine ratios decreased from 0.060+/-0.077 mg/mg in those less than 7 years to 0.041+/-0.033 in the 11- to 14-year group. Urinary Na/Cr ratios were significantly lower in younger age groups compared with the older age group (P<0.05). Urinary K/Cr ratio was highest in younger children, and then steadily decreased with age. There was no correlation between 24-h urinary Ca and Na excretion. The mean Ca/Na ratios significantly decreased with advancing age (P<0.05). The solute/creatinine ratios in the non-fasting urine samples correlated well with the 24-h solute excretion. We provide reference values for urinary Ca/Cr, P/Cr, Mg/Cr, Na/K, K/Cr, and uric acid/creatinine ratios in normal Iranian children. A child's age and ethnicity should be taken into consideration when assessing the urinary solute/creatinine ratios.     

Urinary calcium excretion in healthy children and adolescents

Urinary calcium (Ca) excretion was determined in 1,578 24-h urine samples from 507 healthy children and adolescents (252 boys, 255 girls; 2.8–18.4 years) participating in the DONALD Study and is presented for 32 different age and sex groups. Calciuria values related to body weight (mg/kg per day) were relatively constant except for a transient decrease during puberty in all centiles, with a later onset in boys than girls. Distribution of calciuria (mg/kg per day) was best normalized by log transformation, with an almost constant standard deviation of the log-transformed values. Ca excretion was ≥4 mg/kg per day in 8.6% and ≥6 mg/kg per day in 1.5% of the urine samples. Based on Ca excretion rates of 1,080 pairs of 24-h urine samples from 364 children and adolescents, sensitivity, specificity, and the predictive value for hypercalciuria (≥4 mg/kg per day) in the next urine sample were calculated at three test levels classifying calciuria of the initial urine sample. In summary, this study presents normal values of urinary Ca excretion related to age and sex in a population of healthy German children and adolescents consuming a typical western-style diet. A high level of calciuria in a random urine sample is important in the diagnosis of hypercalciuria. Received: 25 February 1997 / Revised: 28 April 1999 / Accepted: 3 May 1999     

Urinary glycosaminoglycan excretion in healthy and stone-forming children

Both in vivo and in vitro studies suggest that macromolecules excreted in the urine, e. g. glycosaminoglycans (GAGs) may be inhibitors of kidney stone formation. We evaluated urinary GAG excretion in 22 children with calcium oxalate stones [8 with absorptive hypercalciuria, 6 with renal hypercalciuria (RH), 8 with normocalciuria], and in 20 age-matched controls. There was no significant difference between the two groups in the total urinary GAG level. In terms of the various GAG fractions, patients with RH excreted considerably less keratan sulphate and considerably more dermatan sulphate than the other patients and healthy controls. There was no difference between the two groups in condroitin sulphate, heparan sulphate and hyaluronic acid excretion. We conclude that there is no significant correlation between the formation of calcium oxalate stones and urinary GAG excretion. Received January 31, 1995; received in revised form and accepted February 6, 1996     

Urinary calcium excretion in healthy school children

Two hundred and twenty Argentinian primary school children (122 boys, 98 girls, aged 6 – 13 years) were studied to establish reference values of 24-h urinary calcium excretion (UCa) and calcium/creatinine ratio (Ca/Cr) in 24-h urine collections and in first-morning urine samples. Mean UCa excretion was 2.05±1.40 mg/kg per day and the 95th percentile was 4.74 mg/kg per day. UCa excretion was higher in boys than girls (2.33±1.47 and 1.70±1.24 mg/kg per day respectively, P <0.001). Statistically significant differences were found between the 6- to 9-year and the 10- to 13-year age groups (2.37±1.49 vs. 1.73±1.25 mg/kg per day, P <0.001). Mean Ca/Cr ratios in 24-h collections and in first-morning urine samples were 0.129±0.086 and 0.105±0.079 for the group overall (P <0.001). The Ca/Cr ratio in the first-morning urine sample correlated poorly with the 24-h calcium excretion, suggesting that the Ca/Cr ratio in first-morning urine samples cannot replace the 24-h measurement. Received December 22, 1995; received in revised form June 17, 1996; accepted June 18, 1996     

Urinary oxalate and glycolate excretion in healthy infants and children

The molar ratios of oxalate and glycolate over creatinine were determined in single urine samples of 26 infants and 27 children aged 1–5 years. In 135 children aged 5–16 years, two urine specimens were collected, one before breakfast and one at noon. Oxalate was determined by oxalate oxidase, and glycolate was measured by a colorimetric method (improved chromatotropic acid-sulphuric acid assay after prior purification by cation and anion exchanger). Both ratios (expressed in mmol/mol creatinine and analysed on a log-normal basis) were highest in infants 0–6 months old [mean oxalate 147 (95% confidence interval: 60–360), mean glycolate 175 (72–425)]. The mean oxalate ratio was 72 mmol/mol (29–174) at the age of 7–24 months, 44 (19–101) at the age of 2–5 years and 22 (12–40) in adolescents aged 16 years. Molar glycolate ratios were higher, but disclosed the same pattern. Oxalate and glycolate ratios in fasting urines did not differ significantly from those in noon samples (except glycolate in the oldest age group). Oxalate ratios correlated well with glycolate ratios in children up to 5 years of age only. Random urine samples are thus suitable for screening. However, interpretation of data requires use of age-specific reference values that are based on comparable methods.     

Urinary excretion of retinol-binding protein in healthy children and adolescents

Retinol-binding protein (RBP) is a marker of tubular reabsorption in the kidneys. The aim of our study was to investigate urinary RBP excretion in healthy children to obtain reference values related to age and pubertal stage. Overnight samples from 143 subjects (73 girls, 70 boys) aged 10–18 years were investigated. RBP was quantified by a solid-phase sandwich enzyme immunoassay. Both the RBP excretion rate and the RBP/ creatinine ratio (RBP/Cr) showed a skewed distribution. The medians and the 5th–95th percentiles were 38 ng/min (15–127) and 9 μg/mmol (4–23), respectively. The RBP excretion rate and RBP/Cr ratio were similar in both sexes, and linear multiple regression analysis showed no association with age or pubertal stage, although a weak relationship (r = 0.27) was found between RBP excretion rate and age in boys and RBP/Cr ratio and age (r = -0.28) in girls by simple correlation analysis. The correlation between RBP excretion rate and RBP/Cr ratio was 0.76; the RBP excretion rate and RBP/Cr ratio measured on 2 consecutive days, showed a correlation coefficient of 0.84 and 0.88, respectively. We conclude that overnight RBP excretion in children over 10 years shows a low day-to-day variation and, in practical terms, is independent of age, gender and pubertal stage.     

Urinary excretion of urodilatin in healthy children and children with renal disease

Urodilatin (URO) is a natriuretic peptide isolated from human urine which is thought to be produced by distal tubular cells. We measured urinary URO excretion in 50 healthy children and 23 children with acute (ARF), chronic renal failure (CRF), or hereditary tubular disorders, using a specific radioimmunoassay. The mean URO excreted in these four groups was 56, 45, 94, and 121 fmol/min per 1.73 m², respectively (differences between first three groups not significant). The variation in URO excretion was larger in patients with kidney disease than in controls. There were significant correlations between urinary URO and sodium excretion in controls and CRF, but not in ARF. URO excretion also correlated with urine flow rate in CRF. Although no correlation was found between URO excretion and creatinine clearance, urinary URO was increased in some patients with advanced CRF, which suggests stimulated tubular production to compensate for reduced sodium excretion. In view of the therapeutic potential of URO in renal insufficiency, further study of the renal handling of URO is warranted. Received December 4, 1996; received in revised form and accepted June 13, 1997     

Urinary calcium excretion in healthy children and children with primary monosymptomatic nocturnal enuresis

PURPOSE: We investigated the role of urinary Ca excretion in monosymptomatic nocturnal enuresis, and defined normality and intra-individual variability in Ca excretion in healthy children. MATERIALS AND METHODS: We included 46 Danish children with desmopressin resistant nocturnal enuresis and 96 healthy controls. We performed fractional urine collections at home during 2 days in controls or during hospitalization in children with enuresis. Urine volume, osmolality, and Ca and creatinine measurements were performed and Ca-to-creatinine ratios were calculated and compared between groups. Based on nocturnal urine output children with enuresis were characterized as having polyuria (nocturnal urine volume greater than 130% of expected bladder capacity) or not having polyuria. RESULTS: We did not find any differences in controls compared with children with enuresis who did not and did have nocturnal polyuria in daytime Ca excretion (mean +/- SE 0.121 +/- 0.012, 0.078 +/- 0.014 and 0.095 +/- 0.020 mg/mg creatinine), nighttime Ca excretion (0.115 +/- 0.011, 0.092 +/- 0.019 and 0.139 +/- 0.029 mg/mg creatinine) or 24-hour Ca excretion (0.118 +/- 0.011, 0.083 +/- 0.014 and 0.106 +/- 0.020 mg/mg creatinine, respectively). Urinary Ca excretion was not influenced by patient age, sex or body weight and, furthermore, we did not find evidence of diurnal variation. However, we observed considerable intra-individual variability in diurnal, nocturnal and total 24-hour urinary Ca-to-creatinine ratios. CONCLUSIONS: These observations contradict several previous reports and speculations on a role of Ca in the pathogenesis of nocturnal enuresis.     

Urinary citrate excretion in patients with renal calculi

Urinary citrate excretion was measured with a specific enzymatic technique in normal subjects and in an unselected group of patients with recurrent calcium oxalate stones. Hypocitraturia (citrate levels less than those present in 95 per cent of the normal population) was detected in 7 of 46 patients with stones (15 per cent). Hypocitraturia was the only metabolic abnormality in 6 patients.     

Urinary citrate excretion in stone-formers and normal controls.

A specific method was used for the estimation of citrate in 24-hour urine collections from 108 young adult controls, 158 patient controls and 164 stone-formers. Stone-formers excreted significantly less citrate in 24 hours than either patient controls or young adult controls. Stone-formers had a lower concentration of citrate in their urine than either of the control groups. The young adult females exhibited a much greater excretion of citrate relative to calcium than the young males. Because of the ability of citrate to complex with calcium ions and keep them in solution, the relatively low incidence of calcium-containing stones in females under 50 years of age could well be the result of their high excretion of citrate and their increased excretion of this substance relative to calcium.     

Urinary citrate excretion in patients with urolithiasis and normal subjects

Citrate is a normal constituent of urine which combines with calcium to form a soluble salt. Urinary citrate excretion was examined in patients with urolithiasis and normal subjects by a specific enzymatic technique. There was a considerable overlap in the urinary citrate excretion between normal subjects and stone-formers, but the citrate-creatinine ratio, the citrate-calcium ratio and the citrate-magnesium-calcium ratio, which were all highly significantly lower (p less than 0.001) in stone-formers than in controls, proved most reliable in discriminating between these groups.     

Urinary creatinine excretion and protein/creatinine ratios vary by body size and gender in children

Urinary protein/creatinine ratio (Up/cr) is a simple measurement for evaluation of proteinuria. However, exact effects of body size and gender on urinary excretion of creatinine and Up/cr remain unknown. We aimed to clarify their effects. Early morning urine samples were collected from 124 children with urinary tract disorders. Urinary hourly excretion of creatinine, Ucr (in milligrams per hour), urinary hourly excretion of protein per body surface area, Up (milligrams per square meter per hour), and Up/cr (milligrams per milligram) were calculated. Effects of gender, age, body height, body weight and body surface area on Ucr and Up/cr were analyzed, respectively, in a multiple linear regression model. Body surface area and gender affected Ucr (r²=0.842, P<0.0001). Ucr adjusted by body surface area increased as body surface area grew with moderate variation. Up/cr showed a close correlation with Up and was affected by body height and gender as well. The regression equation showed that Up/cr values corresponding to the normal upper limit of Up, i.e., 4 mg/m²/h, in boys and girls 170 cm tall were approximately one third of those in children 80 cm tall (0.121 vs 0.043 for boys, 0.132 vs 0.047 for girls). The present study indicates that estimation of Up/cr needs to include consideration of children’s body height and gender.     

Urinary calcium and oxalate excretion in children

We have established normal values for calcium/creatinine (Ca/Cr) and oxalate/creatinine (Ox/Cr) ratios in 25 infants (aged 1–7 days) and 391 children (aged 1 month to 14.5 years) and compared these with values obtained in 137 children with post-glomerular haematuria and 27 with nephrolithiasis. Oxalate was measured by ion chromatography. Nomograms of Marshall and Robertson were used to calculate urine saturation to calcium oxalate. The Ca/Cr ratio was normally distributed whereas the Ox/Cr ratio had a log-normal distribution. The molar ratio of Ca/Cr was the lowest in the first days of life and the highest between 7 month and 1.5 years (mean±SD=0.39±0.28 mmol/mmol). Following a slight decrease it stabilised by the age of 6 years (0.34±0.19 mmol/mmol). The highest Ox/Cr values were measured during the 1st month of life [geometric mean 133 (range 61–280) mol/mmol], followed by a gradual decrease until 11 years of age [mean 24 (range 6–82) mol/mmol]. Thirty-six haematuric children had hypercalciuria (26%), 23 had absorptive hypercalciuria, 13 renal type. Children with absorptive hypercalciuria on a calcium-restricted diet had significantly higher oxalate excretion than those with renal hypercalciuria and the control group [38 (range 28–49) vs. 22 (range 16–29) and 23 (range 22–27) mol/mol respectively,P<0.01]. Calcium oxalate urine saturation of stone patients was higher than that of patients with haematuria and the normal population (1.18±0.05 vs. 1.06±0.03,P<0.03 and 0.84±0.03,P<0.001 respectively). The measurement of Ca/Cr and Ox/Cr in first-morning urine samples is suitable for screening for hypercalciuria and hyperoxaluria. Interpretation of the values requires age-specific reference values. Both calcium and oxalate determinations should be part of the evaluation of patients with haematuria, hypercalciuria or nephrolithiasis.     

Urinary albumin excretion in Spanish children

We measured urinary albumin excretion in 2,224 school-children (1,168 boys, 1,056 girls) aged 2–18 years, between 1989 and 1990 to establish reference values. We recorded all pathological antecedents and findings from physical examination, including anthropometric parameters and arterial blood pressure. The analytical study included serum total protein, albumin and creatinine. The second-morning urine and the nightly (rest) 10-h urine sample were collected and we determined the concentration of albumin and creatinine. We found a positive statistically significant correlation between the urinary albumin excretion (g/10 h) and age, height, weight and body surface area. We suggest that it would be useful to relate the urinary albumin excretion to body surface area. The mean value for albumin excretion was 3.49 g/ml in boys and 3.63 g/ml in girls. The urinary albumin/creatinine ratio showed a high correlation with the albumin excretion (r=0.958).The following members are co-authors of this report: N. Caballo, M. A. Arias, C. Serna, M. Ramirez and A. Cornejo     

Urinary uric acid excretion in healthy male infants

  Blood and urine samples were collected from 23 healthy term male infants aged 2 – 12 months (mean 6.6 months). Data for establishing urinary uric acid reference values were obtained: urine concentration, 24-h urine output, weight-related urine output, urine output related creatinine, clearance, and fractional excretion. A negative correlation with age was demonstrated for all parameters studied. Received April 1, 1996; received in revised form March 18, 1997; accepted March 20, 1997     

Urinary porphyrin excretion in normal children and adults

The relationship of random urinary porphyrin and creatinine values as functions of age and sex was examined in a normal population. Total urinary porphyrin was measured by a solvent extraction technique, while urinary creatinine was evaluated by an alkaline picrate method. Random urine specimens from 120 healthy patients (81 children and 39 adults) were evaluated. In both pediatric and adult populations, a strong correlation was found between urinary concentrations of porphyrin and creatinine (r = 0.7, P less than 0.0001). Urinary porphyrin excretion in mumol/mol creatinine (micrograms/g) was inversely related to both age (r = -0.59, P less than 0.0001) and weight (r = -0.61, P less than 0.0001) until approximately 9 years of age or 30 kg. Urinary porphyrin excretion in children 9 to 18 years of age was lower than that of younger children (P less than 0.0001) and approached adult values. Sex was not found to be a factor until 9 to 18 years of age, when females had higher urinary creatinine concentrations (P less than 0.05), but lower urinary porphyrin excretions (P less than 0.05) than similarly aged males. The converse was observed when similar values of adult women were compared with those of adult men. Men also had higher urinary porphyrin concentrations than women (P less than 0.01). Men had increased urinary creatinine concentration (P less than 0.05) and decreased porphyrin excretion ratios (P less than 0.05) when compared with males 9 to 18 years of age. Women had significantly lower urinary creatinine (P less than 0.001) and porphyrin (P less than 0.001) concentrations than females 9 to 18 years of age.(ABSTRACT TRUNCATED AT 250 WORDS)     

Urinary N-acetyl-beta-D-glucosaminidase activity in healthy children

Aim: The principal aim was to establish paediatric reference data for the urinary N‐acetyl‐β‐D‐glucosaminidase (U‐NAG) activity. Method and Results: Two hundred and sixty‐two healthy children aged 0–18 years (0–1 month, n = 38; 1 month?1 year, n = 50; 1–3 years, n = 50; 3–6 years, n = 46; 6–10 years, n = 29; 10–18 years, n = 49) had a urine sample collected and the U‐NAG activity was evaluated by using fluorimetry and related to urinary creatinine as a nkat/mmol ratio. A strong age dependence of the U‐NAG/creatinine ratio and its high interindividual variability in children was observed; the highest values of upper reference range being in the 0–1 month and 1 month?1 year groups (134.8 and 50, respectively), which dropped gradually to 7.25 in the oldest age group (10–18 years). Conclusion: The establishment of urinary NAG reference paediatric values is a potentially useful tool for the proper evaluation of renal tubular impairment in children.