Evaluation of variability of proteinuria indices

Fractional excretion of total protein in patients with nephrotic syndrome

BACKGROUND

The urine protein to creatinine ratio (UPCR) correlates well with the 24-h urine protein test (24-h UPT) and is a reliable indicator of proteinuria. However, in nephrotic syndrome, the correlation between the UPCR and the 24-h UPT tends to decrease. To address this, we introduced the fractional excretion of total protein (FETP), which reflects serum total protein and creatinine levels because severe hypoproteinemia and/or elevated serum creatinine levels tend to occur under these conditions. The 24-h UPT corrected for body surface area (BSA) (24-h UPT/BSA) was used to take body size into consideration. The correlation coefficients for 24-h UPT/BSA and FETP and 24-h UPT/BSA and UPCR were calculated. The statistical significance of the differences between these coefficients was also calculated.

METHODS

Thirty-six pediatric patients with nephrotic syndrome were included in this study. The FETP was calculated as total protein clearance/creatinine clearance (%). Correlation coefficients were calculated for 24-h UPT/BSA and FETP and 24-h UPT/BSA and UPCR. The statistical significance of the differences between these coefficients was also calculated.

RESULTS

The mean ± standard error of FETP was 0.11% ± 0.013%. The correlation coefficients of FETP and UPCR with 24-h UPT/BSA were 0.91 and 0.81, respectively. The FETP demonstrated a significantly stronger correlation with 24-h UPT/BSA than with UPCR (p = 0.01).

CONCLUSIONS

The FETP correlated more strongly with 24-h UPT/BSA than with UPCR in patients with nephrotic syndrome. The FETP is a reliable indicator of proteinuria in nephrotic syndrome, especially in patients with severe hypoproteinemia or elevated serum creatinine levels.

Benefits of incorporating urinary protein/creatinine ratio measurement in a school urine screening system: The experience of restructuring the school urinary screening system in Osaka Prefecture, Japan

AIM

School urine screening has been established in several countries of Asia, including Japan, Korea and Taiwan. In Osaka prefectural schools, the urine screening system had some problematic issues including an unclear referral procedure for students with abnormal urinary findings. Therefore, the school urine screening system was reviewed and restructured in 2004. The aim of this study was to assess the improvement in school urine screening through evaluation of the restructured Osaka prefectural school urinary screening system.

METHODS

The Osaka prefectural school urinary screening system was reviewed, mainly considering two points. One was the incorporation of standard urinary protein/creatinine ratio measurement instead of the traditional urine dipstick and urine sediment tests; the second point was that all students requiring further examination were referred to regional nephrologists.

RESULTS

After restructuring, the number of students who were referred to a medical institute for detailed examinations decreased to 10%, although the number of students newly diagnosed with kidney disease and the types of diagnosis did not change. The positive predictive value of screening increased to about 8 times the value before the system restructuring. The reductions enabled students who required further examination to be referred to regional nephrologists and has contributed to a decreased cost for these examinations.

CONCLUSION

Incorporating urinary protein/creatinine ratio measurement into the school urinary screening system, and updating the guiding principles, including referral to nephrology specialists, has enabled the school urinary screening system in Osaka Prefecture to become more efficient and have better cost performance.

The ratios of urinary β2-microglobulin and NAG to creatinine vary with age in children

BACKGROUND

Although urinary biochemical markers can be assessed by their ratio to urinary creatinine (U-Cr) concentration, reference values in adults may not be applicable to children because the amount of Cr excreted varies by body size. We therefore measured the relationship between age and the ratios of urinary β-2-microglobulin (U-β2MG), N-acetyl-β-d-glucosaminidase (U-NAG), calcium (U-Ca) and protein (U-Pr) concentration to those of U-Cr in children.

METHODS

Fifty-seven patients aged >1 year with benign familial hematuria (median age, 6.3 years) were divided into three age groups: 1-4, 5-9, and ≥10 years. Urinary biomarkers were assayed using actual values; ratios to actual U-Cr values; and our standardized metric, namely 100-fold the ratio of serum Cr to U-Cr concentration; and the relationship of each of these to age was determined.

RESULTS

The ratios of U-β2MG, U-NAG and U-Ca to Cr varied significantly by age, being higher in younger than in older children, but the actual and standardized values of each did not vary by age, nor did any measurement of U-Pr.

CONCLUSIONS

The ratios of urinary markers of tubular function, including U-β2MG, U-NAG and U-Ca, to Cr vary by age, being higher in younger children. In contrast, the ratios of urinary markers of glomerular filtration (such as U-Pr)to Cr do not vary by age, making them suitable for corrections relative to Cr.

Restructuring the Ikeda City school urinary screening system: report of a screening survey

BACKGROUND

Annual urinary screening is conducted at municipal kindergartens, elementary schools, and junior high schools in Ikeda City, Osaka, Japan (Ikeda City School System), and the results are reviewed by a general physician, but standards for when to recommend specialist referral have not been clear.

METHODS

In all children attending the Ikeda City School System in 2012, dipstick urinalysis of a first-morning urine specimen was recommended once or twice, and if a second urinalysis showed proteinuria (≥1+), the urinary protein/creatinine ratio was measured. If this showed ≥0.2 g/g of creatinine (g/gCr), it was recommended that the child be evaluated by a specialist at Ikeda City Hospital.

RESULTS

Urinary screening was performed in about 20% (388) of kindergarten, about 90% (5363) of elementary school, and about 86% (2523) of junior high school children living in Ikeda City. Urine samples were obtained from 387, 5349, and 2476 children, respectively. The urinary protein/creatinine ratio was ≥0.2 g/gCr in 13 children, including 1 elementary and 12 junior high children. In these 13 children, chronic nephritic syndrome (CNS) was suspected in 6 junior high school children, and of these, this was a new finding in 5, and renal biopsy was indicated in 3. In Ikeda City, the prevalence of CNS in elementary school children was <0.03%, the prevalence of CNS in junior high school children was 0.29%, and a renal biopsy was indicated in 0.14%. By eliminating the costs associated with assessment of the results by the Ikeda Medical Association, and by directly contracting with the testing company, the expenses paid by Ikeda City for the system itself decreased from 2,508,619 yen to 966,157 yen.

CONCLUSIONS

Incorporating the urinary protein/creatinine ratio into the school urinary screening system in the Ikeda City School System and clarifying standards for specialist referral has enabled restructuring of the system so that is efficient and its effectiveness can be assessed.

Randomised, double-blind, placebo-controlled trial to determine whether steroids reduce the incidence and severity of nephropathy in Henoch-Schonlein Purpura (HSP)

BACKGROUND

The long-term prognosis of Henoch-Schönlein Purpura (HSP) is predominantly determined by the extent of renal involvement. There is no consensus as to whether treatment with prednisolone at presentation can prevent or ameliorate the progression of nephropathy in HSP.

METHODS

Children under 18 years of age with new-onset HSP were randomly assigned to receive prednisolone or placebo for 14 days. The primary outcomes were (a) the presence of proteinuria at 12 months (defined as urine protein : creatinine ratio (UP : UC) >20 mg/mmol) and (b) the need for additional treatment (defined as the presence of hypertension requiring treatment or renal biopsy anomalies or the need for treatment of renal disease) during the 12 month study period.

RESULTS

352 children were randomised. Of those patients with laboratory UP : UC results available at 12 months, 18/123 (15%) patients on prednisolone and 13/124 (10%) patients on placebo had UP : UC >20 mg/mmol. There was no significant difference in the proportion of patients with UP : UC >20 mg/mmol at 12 months between the treatment groups (OR (prednisolone/placebo)=1.46, 95% CI 0.68 to 3.14, n=247), even after adjusting for baseline proteinuria and medications known to affect proteinuria (adjusted OR=1.29, 95% CI 0.58 to 2.82, n=247). Similarly, there was no significant difference in the time needed for additional treatment between the two groups (hazard ratio (HR) (prednisolone/placebo)=0.53, 95% CI 0.18 to 1.59, n=323).

CONCLUSIONS

This is the largest trial of the role of steroids in children with HSP. We found no evidence to suggest that early treatment with prednisolone reduces the prevalence of proteinuria 12 months after disease onset in children with HSP.

TRIAL REGISTRATION NUMBER

ISRCTN71445600.

Mass spectrometry-based proteomics of endoscopically collected pancreatic fluid in chronic pancreatitis research

MS-based investigation of pancreatic fluid enables the high-throughput identification of proteins present in the pancreatic secretome. Pancreatic fluid is a complex admixture of digestive, inflammatory, and other proteins secreted by the pancreas into the duodenum, and thus is amenable to MS-based proteomic analysis. Recent advances in endoscopic techniques, in particular the endoscopic pancreatic function test (ePFT), have improved the collection methodology of pancreatic fluid for proteomic analysis. Here, we provide an overview of MS-based proteomic techniques as applied to the study of pancreatic fluid. We address sample collection, protein extraction, MS sample preparation and analysis, and bioinformatic approaches, and summarize current MS-based investigations of pancreatic fluid. We then examine the limitations and the future potential of such technologies in the investigation of pancreatic disease. We conclude that pancreatic fluid represents a rich reservoir of potential biomarkers and that the study of the molecular mechanisms of chronic pancreatitis may benefit substantially from MS-based proteomics.

Comparison of estimated protein output and urine protein: creatinine ratio in first and second voids with 24-hour urine protein

BACKGROUND

Current UK guidelines for the identification, management and referral of chronic kidney disease advise an early-morning urine sample for the albumin:creatinine ratio or the protein:creatinine ratio (PCR) in order to quantify proteinuria. Estimated protein output (EPO) is an alternative and possibly better method of quantifying proteinuria which takes lean weight into consideration.

METHODS

We carried out a single-centre study of 36 adult patients with proteinuric nephropathy over a period of 18 months. Urinary PCR and EPO estimates of 24-hour urine protein were compared with 24-hour urine collections by Bland-Altman analysis.

RESULTS

Average 24-hour urine protein was 1.6 g (range 0.2-5.1 g). Best agreement with 24-hour protein was for first-void EPO (limits of agreement 0.33-1.59) followed by a second-void EPO (0.40-1.76), then second-void PCR (0.40-2.08) and lastly first-void PCR (0.28-2.03). None of the differences between estimates of urine protein excretion and 24-hour urine protein were statistically significant. All estimates of protein output had wide confidence intervals confirming that spot urine samples, while simple and convenient to do, are imprecise measures of 24-hour urine protein excretion.

CONCLUSION

When estimating 24-hour urine protein from a spot urine sample, EPO may be marginally more accurate than PCR, and first-void urine samples slightly better than second-void urine samples, but a first- or second-void PCR will suffice in most instances.

The Oxford classification of IgA nephropathy: rationale, clinicopathological correlations, and classification

IgA nephropathy is the most common glomerular disease worldwide, yet there is no international consensus for its pathological or clinical classification. Here a new classification for IgA nephropathy is presented by an international consensus working group. The goal of this new system was to identify specific pathological features that more accurately predict risk of progression of renal disease in IgA nephropathy, thus enabling both clinicians and pathologists to improve individual patient prognostication. In a retrospective analysis, sequential clinical data were obtained on 265 adults and children with IgA nephropathy who were followed for a median of 5 years. Renal biopsies from all patients were scored by pathologists blinded to the clinical data for pathological variables identified as reproducible by an iterative process. Four of these variables: (1) the mesangial hypercellularity score, (2) segmental glomerulosclerosis, (3) endocapillary hypercellularity, and (4) tubular atrophy/interstitial fibrosis were subsequently shown to have independent value in predicting renal outcome. These specific pathological features withstood rigorous statistical analysis even after taking into account all clinical indicators available at the time of biopsy as well as during follow-up. The features have prognostic significance and we recommended they be taken into account for predicting outcome independent of the clinical features both at the time of presentation and during follow-up. The value of crescents was not addressed due to their low prevalence in the enrolled cohort.

Estimation of 24-hour urine protein quantity by the morning-urine protein/creatinine ratio

BACKGROUND

Many reports have described a correlation between the morning-urine protein /creatinine ratio (morning urine P/Cr) and the quantity of 24-h urine protein (Up), as well as regression formulas for Up with morning-urine P/Cr. However, there is no universal regression formula that can be used at all facilities. It is still controversial whether a qualitative calculation is required at outpatient clinics. To develop a practical and universal method, we used receiver operating characteristic (ROC) analysis to estimate Up from morning-urine P/Cr.

METHODS

The subjects were 34 children (309 specimens) with kidney disease who had been admitted to Miyazaki Prefectural Hospital. We examined the correlations of P/Cr with Up and Up/body surface area (Up/BSA) using morning and daytime urine. We determined the cutoff values to estimate Up/BSA from morning-urine P/Cr with an ROC analysis. Next, we applied the values to specimens obtained from other facilities to show the universality of this approach.

RESULTS

Up/BSA for samples in one hospital was significantly correlated with morning-urine P/C. When the morning-urine P/Cr ratio is >or=1.0 or >or=2.0, the Up/BSA ratio will exceed 0.5 or 1.0 (g/m(2) per day), respectively, and the efficiency was sufficiently high (efficiency for Up/BSA of >or=0.5: 88.0%, efficiency for Up/BSA of >or=1.0: 90.9%). When we analyzed samples from two other facilities with these cutoff values, both the sensitivity and specificity were greater than 80% for both facilities.

CONCLUSIONS

The use of cutoff values of 1.0 and 2.0 for morning-urine P/Cr determined by ROC analysis could be a universal method for quantitatively estimating Up/BSA >or=0.5 and 1.0, respectively.

Early chronic kidney disease in Aboriginal and non-Aboriginal Australian children: remoteness, socioeconomic disadvantage or race?

Indigenous people suffer substantially more end-stage kidney disease (ESKD), especially Australian Aboriginals. Previous work suggests causal pathways beginning early in life. No studies have shown the prevalence of early markers of chronic kidney disease (CKD) in both Indigenous and non-Indigenous children or the association with environmental health determinants--geographic remoteness and socioeconomic disadvantage. Height, weight, blood pressure, and urinary abnormalities were measured in age- and gender-matched Aboriginal and non-Aboriginal children from elementary schools across diverse areas of New South Wales, Australia. Hematuria was defined as>or=25 red blood cells/microl (>or=1+), proteinuria>or=0.30 g/l (>or=1+), and albuminuria (by albumin:creatinine)>or=3.4 mg/mmol. Remoteness and socioeconomic status were assigned using the Accessibility and Remoteness Index of Australia and Socio-Economic Indexes For Areas. From 2002 to 2004, 2266 children (55% Aboriginal, mean age 8.9 years) were enrolled from 37 elementary schools. Overall prevalence of hematuria was 5.5%, proteinuria 7.3%, and albuminuria 7.3%. Only baseline hematuria was more common in Aboriginal children (7.1 versus 3.6%; P=0.002). At 2-year follow-up, 1.2% of Aboriginal children had persistent hematuria that was no different from non-Aboriginal children (P=0.60). Socioeconomic disadvantage and geographical isolation were neither significant nor consistent risk factors for any marker of CKD. Aboriginal children have no increase in albuminuria, proteinuria, or persistent hematuria, which are more important markers for CKD. This suggests ESKD in Aboriginal people may be preventable during early adult life.

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.

National Kidney Foundation's Kidney Disease Outcomes Quality Initiative clinical practice guidelines for chronic kidney disease in children and adolescents: evaluation, classification, and stratification

OBJECTIVES

A series of new guidelines has been developed by the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative to improve the detection and management of chronic kidney disease (CKD). In most instances of CKD, the earliest manifestations of the disorder may be identified by relatively simple tests. Unfortunately, CKD is often "underdiagnosed," in part because of the absence of a common definition of CKD and a classification of the stages in its progression. The Kidney Disease Outcomes Quality Initiative clinical practice guidelines for CKD evaluation, classification, and stratification provide a basis to remedy these deficits. The specific goals of the guidelines described in this review are to provide: 1) an overview of the clinical practice guidelines as they pertain to children and adolescents, 2) a simple classification of the stages of CKD, and 3) a practical approach to the laboratory assessment of kidney disease in children and adolescents.

METHODS

The guidelines were developed as part of an evidence-based evaluation of CKD and its consequences in patients of all ages. The data that were used to generate the guidelines in this article were extracted from a structured analysis of articles that reported on children with CKD.

RESULTS AND CONCLUSIONS

This review presents the definition and 5-stage classification system of CKD developed by the work group assigned to develop the guidelines, and summarizes the major recommendations regarding the early detection of CKD. Major emphasis is placed on the identification of children and adolescents with CKD by measuring the protein-to-creatinine ratio in spot urine specimens and by estimating the glomerular filtration rate from serum creatinine using prediction equations.

Quantification and longitudinal trends of kidney, renal cyst, and renal parenchyma volumes in autosomal dominant polycystic kidney disease

ABSTRACT.: The aims of this study were to assess the accuracy and reproducibility of volumetric determinations of total kidney, renal cyst, and renal parenchymal volumes, using fast electron-beam computerized tomography scanning, and to determine the rate of change of these volumes. Nine patients with autosomal dominant polycystic kidney disease (ADPKD) and serum creatinine < or = 1.3 mg/dl and/or an initial iothalamate clearance > or = to 60 ml/min per 1.73 m(2) were imaged weekly over a 3-wk period (total of 3 times). Approximately 8 yr later, they returned for follow-up studies. The kidney volume estimation technique involved a manual segmentation (perimeter drawing) of the kidneys and a semiautomatic threshold approach, using a histogram analysis of the peak densities of renal parenchyma and renal cysts. At entry, total kidney and renal cyst volumes correlated positively with age, while renal parenchymal volumes and GFR correlated negatively with age. The average coefficient of variation values for the three initial consecutive measurements of total kidney, renal cyst (actual and as a percent of total volume), and renal parenchymal volume were 3.4, 7.2, 5.3, and 5.6%, respectively. During the 8 yr of follow-up, total kidney and renal cyst volumes increased, while renal parenchymal volumes and GFR declined. The rate of increase in total kidney and renal cyst volumes varied markedly from patient to patient. There was a significant correlation between rate of increase in renal cyst volume and the rate of decline in GFR. The patients with an initial urine protein/osmolality ratio >0.13 mg/L per mosmol per kg had a significantly higher increase in renal volume and decline in GFR than those with a lower ratio. In summary, the results of this pilot study suggest that: (1) electron-beam computerized tomography is capable of measuring total kidney, renal cyst, and renal parenchymal volumes reproducibly; (2) total kidney and renal cyst volumes increase, while parenchymal volumes decrease with time; (3) the increase in cyst volume correlates best with the decline in renal function; and (4) renal volumes appear to be good surrogate markers for disease progression in ADPKD.

Diet, indicators of kidney disease, and later mortality among older persons in the NHANES I Epidemiologic Follow-Up Study

OBJECTIVES

The purpose of this study was to determine whether diet adversely affected survival among 2572 older persons with indicators of kidney disease in a population-based cohort. Average follow-up time for survivors, of whom 1453 (57%) had died at analysis, was 14.5 years.

METHODS

Kidney disease indicators were a "yes" response to "Has a doctor ever told you that you have kidney disease or renal stones?" and/or trace or greater amounts of protein in urine. Dietary protein intakes were calculated from 24-hour recalls.

RESULTS

Cox proportional hazards models were used, stratified by sex, with age, body mass index, blood pressure, education, smoking status, total caloric intake, and diabetes mellitus as covariates. Relative risk of total mortality with an additional 15 g of protein per day was 1.25 (95% confidence interval [CI] = 1.09, 1.42) among White men with kidney disease indicators, vs 1.00 (95% CI = 0.95, 1.06) among those without them; relative risks of renal-related mortality were 1.32 (95% CI = 0.97, 1.79) and 0.95 (95% CI = 0.81, 1.11), respectively. No significant differences were found for White women.

CONCLUSIONS

Once chronic renal disease is present, diet may be associated with earlier mortality in White males.