The influence of urinary flow rate in children on excretion of markers used for assessment of renal damage: albumin, gamma-glutamyl transpeptidase, N-acetyl-beta-D -glucosaminidase, and alpha1-microglobulin

Equine urinary N-acetyl-β-D-glucosaminidase assay validation and correlation with other markers of kidney injury

Detection of equine acute kidney injury (AKI) is hindered by limited markers of early renal damage in horses. N-acetyl-β-D-glucosaminidase (NAG), a lysosomal enzyme in renal tubular epithelium released into urine during tubular insult, has shown promise for early identification of AKI in humans and other species. We validated an assay for NAG in equine urine and measured urinary NAG in 7 azotemic and 7 non-azotemic client-owned adult horses. The enzymatic NAG assay was validated using within- and between-run coefficients of variation (CVs), recovery following standard addition, and linearity of dilution. Intra- and inter-run CVs (21% and 3.2%, respectively), average recovery following standard addition (99-109%), and linearity under serial dilution (R² = 0.997) were satisfactory. Urine NAG index was significantly correlated with urinary fractional excretion of sodium (FE_Na; ρ = 0.76, p < 0.001) and plasma creatinine (ρ = 0.74, p = 0.001). Median urine NAG indices were higher in azotemic horses (p = 0.006), in horses with increased urinary FE_Na (p = 0.006), and in horses with increased urine gamma-glutamyl transferase index (p = 0.032). Urine NAG can be measured in horses and shows positive correlation with 2 current renal biomarkers. Additional work is needed to establish normal equine reference intervals and characterize the increase of urine NAG index in horses in relation to tubular injury.

Dental composite materials and renal function in children

OBJECTIVE

To examine whether greater exposure to resin-based composite materials, which may intra-orally release bisphenol A (BPA), is associated with worse renal function outcomes in children.

DESIGN

Prospective multi-centre study.

SETTING

Community health dental clinics in Boston and Maine from 1997-2005.Subjects and methods Five hundred and thirty-four New England Children's Amalgam Trial participants aged six to ten years were randomised to treatment with amalgam or resin-based composite restorations over five years of follow-up.

INTERVENTIONS

Restorations were placed according to treatment arm, and sealants placed per standard of care. Cumulative composite exposure was calculated using surface-years (each treated surface weighted by number years present).

MAIN OUTCOME MEASURES

Urinary excretion of albumin, gamma-glutamyl transpeptidase (gamma-GT), and N-acetyl-β-D-glucosaminidase (NAG) were available for 417 children.

RESULTS

Analysis of covariance showed no association between exposure to dental composites, polyacid-modified compomer, or flowable composite dental sealants and preventative resin restorations with levels of renal function. There was no association between composite materials and thresholds indicating renal damage in logistic regression models.

CONCLUSIONS

This study found no harmful associations between dental composite materials and renal function in children. Therefore, concerns about renal function need not be a consideration in the choice of dental restoration material or placement of preventative dental sealants.

Methodological considerations with the use of urine samples for assessment of mercury excretion and markers of renal damage

OBJECTIVE

To provide recommendations for design and analysis of studies using urine specimens to evaluate renal function or mercury excretion in children.

METHODS

An analysis of mercury, albumin, γ-glutamyl transpeptidase (γ-GT) and N-acetyl-β-D-glucosaminidase (NAG) concentrations was carried out.

RESULTS

Mercury concentration and creatinine-corrected renal markers were higher in daytime compared with overnight samples. Excretion rates increased with urinary flow rate. γ-GT and NAG concentrations decreased with storage time at -20°C. Differences by age, sex and race were noted.

CONCLUSIONS

We recommend use of these creatinine-corrected markers and collection of timed overnight urine samples, stored at -70°C, with control for urinary flow rate, age, sex and race in statistical models.

Effect of storage time at -20°C on markers used for assessment of renal damage in children: albumin, γ-glutamyl transpeptidase, N-acetyl-β-D-glucosaminidase and α1-microglobulin

OBJECTIVE

The objective of this study is to examine the influence of storage time at -20°C on the concentration of albumin, γ-glutamyl transpeptidase (γ-GT), N-acetyl-β-D-glucosaminidase (NAG), α(1)-microglobulin (A1M) and creatinine in a large sample of healthy children.

MATERIAL AND METHODS

The New England Children's Amalgam Trial followed 534 children, aged 6-10 at baseline, for 5 years, with annual urine collections. Urine samples were analysed for creatinine, albumin, γ-GT, NAG and A1M concentrations. Repeated measures analysis of covariance was used to model the effect of storage time on these concentrations.

RESULTS

The γ-GT concentration decreased significantly with storage time at -20°C. There was also a limited decrease in NAG. Albumin, A1M and creatinine concentrations did not appear to be affected by storage time at -20°C.

CONCLUSIONS

If it is necessary to interpret results from samples stored for a long time at -20°C, it is advisable to account for storage time in statistical models.

Tubular expression of KIM-1 does not predict delayed function after transplantation

Injured epithelial cells of the proximal tubule upregulate the glycoprotein kidney injury molecule 1 (KIM-1), suggesting its potential as a biomarker of incipient kidney allograft injury. It is unknown whether KIM-1 expression changes in kidney allografts with delayed graft function (DGF), which often follows ischemia-reperfusion injury. Here, we prospectively measured KIM-1 RNA and protein expression in preperfusion biopsies of 30 living- and 85 deceased-donor kidneys and correlated the results with histologic and clinical outcomes after transplantation. We detected KIM-1 expression in 62% of deceased-donor kidneys and only 13% of living-donor kidneys (P < 0.0001). The level of KIM-1 expression before reperfusion correlated inversely with renal function at the time of procurement and correlated directly with the degree of interstitial fibrosis. Surprising, however, we did not detect a significant correlation between KIM-1 staining intensity and the occurrence of DGF. Our findings are consistent with a role for KIM-1 as an early indicator of tubular injury but do not support tissue KIM-1 measurement before transplantation to identify kidneys at risk for DGF.

Tubular marker excretion in children from families with Balkan nephropathy

Balkan nephropathy (BN) has not been described in children; however, some previous studies in children from families with BN have revealed abnormalities of the urinary tract. In this study, urinary excretion of beta2-microglobulin, N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyl transpeptidase (GGT) was studied three times a year: spring, autumn, and winter, during a 3-year period, in 703 healthy children, initial age 9-13, from endemic and nonendemic settlements around the South Morava River. Beta-2-microglobulin excretion in urine, in all three seasons, was highest in children from families with BN compared with the excretion in children from the city, nonendemic villages, and those from nonendemic families. Increased urinary GGT excretion in children from endemic villages in October was higher than in children from the city and control villages, being the same in both endemic and nonendemic families. However, in February, it was similar in children from the city, endemic, and control villages. In conclusion, children from families with BN excreted significantly more beta2-microglobulin in all three seasons (spring, autumn, winter) of the study, in multivariate analysis significant for family status, gender, and the season (p < 0.001). NAG emerged as a potentially useful marker for seasonal exposure to an environmental nephrotoxin.

IL-18 and urinary NGAL predict dialysis and graft recovery after kidney transplantation

Current methods for predicting graft recovery after kidney transplantation are not reliable. We performed a prospective, multicenter, observational cohort study of deceased-donor kidney transplant patients to evaluate urinary neutrophil gelatinase-associated lipocalin (NGAL), IL-18, and kidney injury molecule-1 (KIM-1) as biomarkers for predicting dialysis within 1 wk of transplant and subsequent graft recovery. We collected serial urine samples for 3 d after transplant and analyzed levels of these putative biomarkers. We classified graft recovery as delayed graft function (DGF), slow graft function (SGF), or immediate graft function (IGF). Of the 91 patients in the cohort, 34 had DGF, 33 had SGF, and 24 had IGF. Median NGAL and IL-18 levels, but not KIM-1 levels, were statistically different among these three groups at all time points. ROC curve analysis suggested that the abilities of NGAL or IL-18 to predict dialysis within 1 wk were moderately accurate when measured on the first postoperative day, whereas the fall in serum creatinine (Scr) was not predictive. In multivariate analysis, elevated levels of NGAL or IL-18 predicted the need for dialysis after adjusting for recipient and donor age, cold ischemia time, urine output, and Scr. NGAL and IL-18 quantiles also predicted graft recovery up to 3 mo later. In summary, urinary NGAL and IL-18 are early, noninvasive, accurate predictors of both the need for dialysis within the first week of kidney transplantation and 3-mo recovery of graft function.

Circadian rhythms of diuresis, proteinuria and natriuresis in children with chronic glomerular disease

The aim of our study was to examine diurnal variation in urine volume (UV) output, proteinuria (UPRT), urine creatinine (UCr) and urine sodium ion excretion (UNa) in children with chronic glomerulopathy. In 56 patients (20 boys/36 girls, aged 11.7 +/- 0.6 years) samples for UPRT, UCr and UNa were collected during the day and night, with continuous ambulatory blood pressure (BP) monitoring. On the basis of creatinine clearance (CrCl) the patients were divided into group I (n = 44, with CrCl 131 +/- 3.6 ml/min per 1.73 m(2) body surface area), or group II (n = 12, with CrCl 44.6 +/- 7.7 ml/min per 1.73 m(2) body surface area). Nocturnal polyuria was defined as night time UV >or= 35% of the 24 h UV. Age, gender, body mass index of the patients, 24 h UV, UCr and UNa were similar in both groups. However, arterial hypertension and nocturnal polyuria were widespread (P < 0.01) in group II. In addition, proteinuria was higher (P < 0. 05) in group II. The nocturnal decline in CrCl, UV, UPRT and UNa was significantly attenuated (P < 0.005) in patients in group II compared with those in group I. The night time mean arterial pressure (MAP), as well as the night/day ratios of MAP, UV, UPRT and UNa, showed negative associations with CrCl. Our findings strongly suggest that renal function diurnal variation and nocturnal MAP are related to decreased glomerular filtration rate at the time of examination.