Average creatinine-urea clearance: revival of an old analytical technique?

Background

Creatinine-based equations such as the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) are recommended for estimating glomerular filtration rate (eGFR) in clinical practice, but have reduced performance in advanced stages of chronic kidney disease. However, only rarely studies have evaluated the performance of eGFR by measuring the average of the urinary clearances of creatinine and urea (mCl_UN-cr) compared with the eGFR equations.

Methods

This cross-sectional study evaluated the usefulness of mCl_UN-cr in a population of 855 participants who performed a GFR measurement by urinary inulin clearance. The performance of mCl_UN-cr was compared with those of CKD-EPI 2009 and CKD-EPI 2021, considering three criteria: bias, precision and accuracy.

Results

In the whole sample, the mCl_UN-cr performed similarly to CKD-EPI equations (2009 and 2021) [precision: 11.5 (95% CI 10.5; 12.5) vs 19.0 (95% CI 17.2; 20.1) and 19.1 (95% CI 17.4; 20.4), and accuracy P₃₀: 97.0 (95% CI 95.8; 98.0) vs 82.0 (95% CI 79.2; 84.4) and 77.2 (95% CI 74.5; 80.0)]. The CKD-EPI equations (2009 and 2021) had the best performance when mGFR was >60 mL/min/1.73 m². In contrast, the mCl_UN-cr performed better than others with lowest mGFR values, more noticeable when mGFR was <60 mL/min/1.73 m².

Conclusions

The study described the best performance of mCl_UN-cr at GFR levels below 60 mL/min/1.73 m² and a satisfactory result in the overall cohort. The findings point to a role of this tool, especially for estimating GFR in chronic kidney disease patients in developing countries, when reference measurement of GFR is not available.

MO385: Performance of Creatinine-Based Equations to Estimate Glomerular Filtration Rate in White and Black Subjects From Europe, Brazil and Africa

BACKGROUND AND AIMS

Current Glomerular filtration rate (GFR) estimating equations based on serum creatinine are facing increased criticism due to the inclusion of a race correction in black Americans with the CKD-EPI equation (CKD-EPIASR, A = Age, S = Sex, R = Race). A new equation without race (CKD-EPIAS) has been proposed. However, this equation was developed mainly from US cohorts. The performance of this new equation has been poorly compared with current European-developed creatinine-based equations, i.e. the Lund-Malmö Revised (LMR), and the new European Kidney Function Consortium (EKFC)

METHOD

Data from subjects over 18 years, representing 11 cohorts from Europe (previously described as the EKFC dataset, n = 13 856), and enhanced with data from Brazil (n = 100), France (n = 4429) and Africa [Democratic Republic of Congo (DRC) and Côte d'Ivoire, n = 508] were considered (n = 18 893 for the whole cohort). The EKFC cohort was considered as non-black population. All data from Africa derived from black individuals. From France, 964 subjects were self-reported as black (=Blacks from Paris). Measured GFR as a reference method and IDMS creatinine results were available. Median bias (eGFR—mGFR) with 95% confidence intervals (CI), imprecision (interquartile range: IQR), and P30 accuracy (percentage of eGFR-values within ± 30% of mGFR) with 95% CI were calculated.

RESULTS

Results are summarized in Table.

CONCLUSION

The new CKD-EPIAS has been launched in the USA for societal reasons and is now recommended by US guidelines. However, in Europe and Africa, its performance was suboptimal. The EKFC equation, using the usual Q values, or population-specific Q values (when available), displays the best performance over the whole age range for populations in Europe and Africa.

SOBREVIDA DOS PACIENTES COM COVID-19 ADMITIDOS NAS UNIDADES DE TERAPIA INTENSIVA DO HOSPITAL GERAL DE CAXIAS DO SUL

Introdução/Objetivo

Métodos

Resultados

Conclusão

Performance of creatinine-based equations to estimate glomerular filtration rate with a methodology adapted to the context of drug dosage adjustment

AIM

The Cockcroft-Gault (CG) creatinine-based equation is still used to estimate glomerular filtration rate (eGFR) for drug dosage adjustment. Incorrect eGFR may lead to hazardous over- or underdosing METHODS: In a cross-sectional analysis, CG was validated against measured GFR (mGFR) in 14,804 participants and compared with the Modification-of-Diet-in-Renal-Diseases (MDRD), Chronic-Kidney-Disease-Epidemiology (CKD-EPI), Lund-Malmö-Revised (LMR), and European-Kidney-Function-Consortium (EKFC) equations. Validation focused on bias, imprecision, and accuracy (percentage of estimates within ±30% of mGFR, P30), overall and stratified for mGFR, age, and body mass index at mGFR <60 mL/min, as well as classification in mGFR stages.

RESULTS

The CG equation performed worse than the other equations, overall and in mGFR, age and BMI subgroups in terms of bias (systematic overestimation), imprecision and accuracy except for patients ≥65 years where bias and P30 were similar to MDRD and CKD-EPI, but worse than LMR and EKFC. In subjects with mGFR<60 mL/min and at BMI [18.5-25[kg/m² , all equations performed similarly and for BMI<18.5kg/m² CG and LMR had the best results though all equations had poor P30-accuracy. At BMI≥25kg/m² the bias of the CG increased with increasing BMI (+17.2mL/min at BMI≥40kg/m² ). The four more recent equations also classified mGFR stages better than CG.

CONCLUSIONS

The CG equation showed poor ability to estimate GFR overall and in analyses stratified for GFR, age, and BMI. CG was inferior to correctly classify the patients in the mGFR staging compared to more recent creatinine-based equations.

Development and Validation of a Modified Full Age Spectrum Creatinine-Based Equation to Estimate Glomerular Filtration Rate : A Cross-sectional Analysis of Pooled Data

BACKGROUND

The Chronic Kidney Disease in Children Study (CKiD) equation for children and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for adults are recommended serum creatinine (SCr)-based calculations for estimating glomerular filtration rate (GFR). However, these equations, as well as their combination, have limitations, notably the problem of implausible changes in GFR during the transition from adolescence to adulthood and overestimation of GFR in young adults. The full age spectrum (FAS) equation addresses these issues but overestimates GFR when SCr levels are low.

OBJECTIVE

To develop and validate a modified FAS SCr-based equation combining design features of the FAS and CKD-EPI equations.

DESIGN

Cross-sectional analysis with separate pooled data sets for development and validation.

SETTING

Research and clinical studies (n = 13) with measured GFR available.

PATIENTS

11 251 participants in 7 studies (development and internal validation data sets) and 8378 participants in 6 studies (external validation data set).

MEASUREMENTS

Clearance of an exogenous marker (reference method), SCr level, age, sex, and height were used to develop a new equation to estimate GFR.

RESULTS

The new European Kidney Function Consortium (EKFC) equation is a FAS equation with low bias (-1.2 mL/min/1.73 m² [95% CI, -2.7 to 0.0 mL/min/1.73 m²] in children and -0.9 mL/min/1.73 m² [CI, -1.2 to -0.5 mL/min/1.73 m²] in adults) across the FAS (2 to 90 years) and SCr range (40 to 490 µmol/L [0.45 to 5.54 mg/dL]) and with fewer estimation errors exceeding 30% (6.5% [CI, 3.8% to 9.1%] in children and 3.1% [CI, 2.5% to 3.6%] in adults) compared with the CKiD and CKD-EPI equations.

LIMITATION

No Black patients were included.

CONCLUSION

The new EKFC equation shows improved accuracy and precision compared with commonly used equations for estimating GFR from SCr levels.

PRIMARY FUNDING SOURCE

Swedish Research Council (Vetenskapsrådet).

Comparison of iohexol plasma clearance formulas vs. inulin urinary clearance for measuring glomerular filtration rate

OBJECTIVES

The one-compartment iohexol plasma clearance has been proposed as a reliable alternative to renal inulin clearance. However, this method's performance depends on the formula used to calculate glomerular filtration rate (GFR). This study reports on performance comparisons between various mathematical formulas proposed for iohexol plasma clearance vs. inulin urinary clearance.

METHODS

GFR was simultaneously determined by inulin and iohexol clearance in 144 participants (age: 10-84 years; glomerular filtration rate: 15-169 mL/min/1.73 m²). A retrospective cross-sectional study evaluated the performance of four formulas proposed to calculate plasma iohexol clearance (Brøchner-Mortensen, Fleming et al., Jødal-Brøchner-Mortensen, and Ng-Schwartz-Munoz). The performance of each formula was assessed using bias, precision (standard deviation of the bias), accuracy (percentage iohexol within 5, 10, and 15%), root mean square error, and concordance correlation coefficient vs. renal inulin clearance as reference.

RESULTS

Regarding accuracy, there was no difference in root mean square error (RMSE), P₅, P₁₀, or P₁₅ between the four formulas. The four concordance correlation coefficients (CCC) between the value from each formula and in-GFR were high and not significantly different. At in-GFR ≥90 mL/min/1.73 m², Ng-Schwartz-Munoz formula performed slightly better than other formulas regarding median bias (-0.5; 95% CI [-3.0 to 2.0] and accuracy P₁₅ (95.0; 95% CI [88.0-100.0]).

CONCLUSIONS

The studied formulas were found equivalent in terms of precision and accuracy, but the Ng-Schwartz-Munoz formula improved the accuracy at higher levels of in-GFR.

Estimating glomerular filtration rate at the transition from pediatric to adult care

The current Kidney Disease Improving Global Outcomes (KDIGO) guidelines recommend the use of the bedside creatinine-based Chronic Kidney Disease in Children (CKiD) equation to estimate glomerular filtration rate (GFR) in children and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation in adults. However, this approach causes implausible changes in estimated GFR (eGFR) at the transition from pediatric to adult care. We investigated the performance of the KDIGO strategy and various creatinine-based eGFR equations in a cross-sectional dataset of 5,764 subjects (age 10-30 years), using directly measured GFR (mGFR) as reference. We also evaluated longitudinal GFR slopes in 136 subjects who transitioned to adult care. Implausible changes in eGFR resulted from the large overestimation (bias=+21 mL/min/1.73m²) and poor precision of the CKD-EPI equation in the 18-20 year age group, compared to CKiD in the 16-18 year age group (bias=-2.7 mL/min/1.73m²), resulting in a mean change of 23 mL/min/1.73m² at the transition to adult care. Averaging the CKiD and CKD-EPI estimates in young adults only partially mitigated this issue. The Full Age Spectrum equation (with and without height), the Lund-Malmö Revised equation, and an age-dependent weighted average of CKiD and CKD-EPI resulted in much smaller changes in eGFR at the transition (change of 0.6, -2.1, -0.9 and -1.8 mL/min/1.73m², respectively). The longitudinal analysis revealed a significant difference in average GFR slope between mGFR and the KDIGO strategy (-2.2 vs. +2.9 mL/min/1.73 m²/year), which was not observed with the other approaches. These results suggest that the KDIGO recommendation for GFR estimation at the pediatric-adult care transition should be revisited.

Estimating glomerular filtration rate for the full age spectrum from serum creatinine and cystatin C

Background

We recently published and validated the new serum creatinine (Scr)-based full-age-spectrum equation (FAS crea ) for estimating the glomerular filtration rate (GFR) for healthy and kidney-diseased subjects of all ages. The equation was based on the concept of normalized Scr and shows equivalent to superior prediction performance to the currently recommended equations for children, adolescents, adults and older adults.

Methods

Based on an evaluation of the serum cystatin C (ScysC) distribution, we defined normalization constants for ScysC ( Q cysC  =   0.82 mg/L for ages <70 years and Q cysC  =   0.95 mg/L for ages ≥70 years). By replacing Scr/ Q crea in the FAS crea equation with ScysC/ Q cysC , or with the average of both normalized biomarkers, we obtained new ScysC-based (FAS cysC ) and combined Scr-/ScysC-based FAS equations (FAS combi ). To validate the new FAS cysC and FAS combi we collected data on measured GFR, Scr, ScysC, age, gender, height and weight from 11 different cohorts including n  = 6132 unique white subjects (368 children, aged ≤18 years, 4295 adults and 1469 older adults, aged ≥70 years).

Results

In children and adolescents, the new FAS cysC equation showed significantly better performance [percentage of patients within 30% of mGFR (P30) = 86.1%] than the Caucasian Asian Paediatric Adult Cohort equation (P30 = 76.6%; P < 0.0001), or the ScysC-based Schwartz equation (P30 = 68.8%; P < 0.0001) and the FAS combi equation outperformed all equations with P30 = 92.1% (P < 0.0001). In adults, the FAS cysC equation (P30 = 82.6%) performed equally as well as the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI cysC ) (P30 = 80.4%) and the FAS combi equation (P30 = 89.9%) was also equal to the combined CKD-EPI equation (P30 = 88.2%). In older adults, FAS cysC was superior (P30 = 88.2%) to CKD-EPI cysC (P30 = 84.4%; P < 0.0001) and the FAS combi equation (P30 = 91.2%) showed significantly higher performance than the combined CKD-EPI equation (P30 = 85.6%) (P < 0.0001).

Conclusion

The FAS equation is not only applicable to all ages, but also for all recommended renal biomarkers and their combinations.

Data on the relation between renal biomarkers and measured glomerular filtration rate

The data presented in this article are related to the research article entitled "The Diagnostic Value of Rescaled Renal Biomarkers Serum Creatinine and Serum Cystatin C and their Relation with Measured Glomerular Filtration Rate" (Pottel et al. (2017) [1]). Data are presented demonstrating the rationale for the normalization or rescaling of serum cystatin C, equivalent to the rescaling of serum creatinine. Rescaling biomarkers brings them to a notionally common scale with reference interval [0.67-1.33]. This article illustrates the correlation between rescaled biomarkers serum creatinine and serum cystatin C by plotting them in a 2-dimensional graph. The diagnostic value in terms of sensitivity and specificity with measured Glomerular Filtration Rate as the reference method is calculated per age-decade for both rescaled biomarkers. Finally, the interchangeability between detecting impaired kidney function from renal biomarkers and from the Full Age Spectrum FAS-estimating GFR-equation and measured GFR using a fixed and an age-dependent threshold is shown.

The diagnostic value of rescaled renal biomarkers serum creatinine and serum cystatin C and their relation with measured glomerular filtration rate

BACKGROUND

Serum creatinine (Scr) is the major contributing variable in glomerular filtration rate (GFR) estimating equations. Serum cystatin C (ScysC) based GFR estimating (eGFR)-equations have also been developed. The present study investigates the relation between 'rescaled' levels of these renal biomarkers (with reference interval of [0.67-1.33]) and measured GFR (mGFR).

METHODS

We evaluated the diagnostic ability to detect impaired kidney function of the rescaled renal biomarkers in 8584 subjects from 12 cohorts with measured GFR, standardized Scr and ScysC. We calculated sensitivity and specificity of the rescaled biomarkers to identify kidney disease, with reference to a fixed (60mL/min/1.73m²) as well as an age-dependent threshold for mGFR.

RESULTS

The upper reference limit of 1.33 for rescaled renal biomarkers is closely related to the age-dependent threshold for defining kidney status by mGFR with sensitivity and specificity for the rescaled biomarkers close to 90% for all ages. If the fixed threshold of 60mL/min/1.73m² for mGFR is used, then lower specificity in children and sensitivity in older adults are observed.

CONCLUSIONS

Impaired kidney function can be diagnosed by rescaled renal biomarkers instead of eGFR-equations using the fixed threshold of 1.33 for all ages, consistent with an age-dependent threshold of mGFR.

Age-dependent reference intervals for estimated and measured glomerular filtration rate

Background

Defining mean and reference intervals for glomerular filtration rate (GFR) has been the subject of only a limited number of studies and review articles, with contradicting statements about the mean. Normal measured GFR (mGFR) values of ∼120–130 mL/min/1.73 m² have long been the referenced values for young adults but seem to be too high according to recent studies. Reference intervals are difficult to define because of the age decline of GFR, which is also observed in healthy subjects. Little data are available for subjects >70 years of age.

Methods

Based on the reference intervals for serum creatinine (SCr) and the recently published full-age spectrum (FAS) equation, we define simple age-dependent equations for the reference limits of GFR. The mGFR of 633 living potential kidney donors was used to validate the new formulae that define the reference interval.

Results

The reference limits for estimated GFR (eGFR), calculated by entering the reference limits for SCr into the FAS equation closely correspond with published reference limits for mGFR. Of the mGFRs of potential living kidney donors, 97.2% lie between the newly defined reference limits for GFR.

Conclusion

SCr reference limits may serve to define age-dependent reference limits for eGFR and mGFR.

Trajectories and Predictors of Allograft Dysfunction after Renal Transplantation in Children

BACKGROUND

The survival rates of renal transplant children are indeed on the rise, but it is still important to ensure that there is optimal renal function in these children in all their future growing years. The number of functioning nephrons and the graft ability to adapt to an increasing demand during body growth seem to be the most important factors for long-term allograft function. This study examined the long-term change in the glomerular filtration rate in a pediatric kidney transplant cohort and the importance of the recipient and donor ages in predicting transplant outcome.

METHODS

Data on 67 renal transplant children who underwent 278 inulin-clearance measurements between 2000 and 2010 were examined. A longitudinal latent class model was used to identify renal function trajectories and classify the children.

RESULTS

This model identified 3 trajectories of renal allograft function after pediatric kidney transplantation: 'low and decreasing', 'moderate and stable', and 'high and sharply decreasing'. The probability of belonging to the low and decreasing trajectory - that is, the poorer outcome - was lower in recipients of grafts from living versus deceased donor (adjusted OR (aOR) 0.02; p = 0.03). This probability increased with recipient age (aOR 1.20 per year of recipient ageing; p = 0.07) and donor-recipient age-difference (aOR 1.13 per additional year; p = 0.07).

CONCLUSION

This study suggests that donation from living donors and from younger donors are favorable factors for long-term allograft function.

Comparison of the Schwartz and CKD-EPI Equations for Estimating Glomerular Filtration Rate in Children, Adolescents, and Adults: A Retrospective Cross-Sectional Study

BACKGROUND

Estimating kidney glomerular filtration rate (GFR) is of utmost importance in many clinical conditions. However, very few studies have evaluated the performance of GFR estimating equations over all ages and degrees of kidney impairment. We evaluated the reliability of two major equations for GFR estimation, the CKD-EPI and Schwartz equations, with urinary clearance of inulin as gold standard.

METHODS AND FINDINGS

The study included 10,610 participants referred to the Renal and Metabolic Function Exploration Unit of Edouard Herriot Hospital (Lyon, France). GFR was measured by urinary inulin clearance (only first measurement kept for analysis) then estimated with isotope dilution mass spectrometry (IDMS)-traceable CKD-EPI and Schwartz equations. The participants' ages ranged from 3 to 90 y, and the measured GFRs from 3 to 160 ml/min/1.73 m2. A linear mixed-effects model was used to model the bias (mean ratio of estimated GFR to measured GFR). Equation reliability was also assessed using precision (interquartile range [IQR] of the ratio) and accuracy (percentage of estimated GFRs within the 10% [P10] and 30% [P30] limits above and below the measured GFR). In the whole sample, the mean ratio with the CKD-EPI equation was significantly higher than that with the Schwartz equation (1.17 [95% CI 1.16; 1.18] versus 1.08 [95% CI 1.07; 1.09], p < 0.001, t-test). At GFR values of 60-89 ml/min/1.73 m2, the mean ratios with the Schwartz equation were closer to 1 than the mean ratios with the CKD-EPI equation whatever the age class (1.02 [95% CI 1.01; 1.03] versus 1.15 [95% CI 1.13; 1.16], p < 0.001, t-test). In young adults (18-40 y), the Schwartz equation had a better precision and was also more accurate than the CKD-EPI equation at GFR values under 60 ml/min/1.73 m2 (IQR: 0.32 [95% CI 0.28; 0.33] versus 0.40 [95% CI 0.36; 0.44]; P30: 81.4 [95% CI 78.1; 84.7] versus 63.8 [95% CI 59.7; 68.0]) and also at GFR values of 60-89 ml/min/1.73 m2. In all patients aged ≥65 y, the CKD-EPI equation performed better than the Schwartz equation (IQR: 0.33 [95% CI 0.31; 0.34] versus 0.40 [95% CI 0.38; 0.41]; P30: 77.6 [95% CI 75.7; 79.5] versus 67.5 [95% CI 65.4; 69.7], respectively). In children and adolescents (2-17 y), the Schwartz equation was superior to the CKD-EPI equation (IQR: 0.23 [95% CI 0.21; 0.24] versus 0.33 [95% CI 0.31; 0.34]; P30: 88.6 [95% CI 86.7; 90.4] versus 29.4 [95% CI 26.8; 32.0]). This study is limited by its retrospective design, single-center setting with few non-white patients, and small number of patients with severe chronic kidney disease.

CONCLUSIONS

The results from this study suggest that the Schwartz equation may be more reliable than the CKD-EPI equation for estimating GFR in children and adolescents and in adults with mild to moderate kidney impairment up to age 40 y.

An estimated glomerular filtration rate equation for the full age spectrum

BACKGROUND

Glomerular filtration rate (GFR) is accepted as the best indicator of kidney function and is commonly estimated from serum creatinine (SCr)-based equations. Separate equations have been developed for children (Schwartz equation), younger and middle-age adults [Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation] and older adults [Berlin Initiative Study 1 (BIS1) equation], and these equations lack continuity with ageing. We developed and validated an equation for estimating the glomerular filtration rate that can be used across the full age spectrum (FAS).

METHODS

The new FAS equation is based on normalized serum creatinine (SCr/Q), where Q is the median SCr from healthy populations to account for age and sex. Coefficients for the equation are mathematically obtained by requiring continuity during the paediatric-adult and adult-elderly transition. Research studies containing a total of 6870 healthy and kidney-diseased white individuals, including 735 children, <18 years of age, 4371 adults, between 18 and 70 years of age, and 1764 older adults, ≥70 years of age with measured GFR (inulin, iohexol and iothalamate clearance) and isotope dilution mass spectrometry-equivalent SCr, were used for the validation. Bias, precision and accuracy (P30) were evaluated.

RESULTS

The FAS equation was less biased [-1.7 (95% CI -3.4, -0.2) versus 6.0 (4.5, 7.5)] and more accurate [87.5% (85.1, 89.9) versus 83.8% (81.1, 86.5)] than the Schwartz equation for children and adolescents; less biased [5.0 (4.5, 5.5) versus 6.3 (5.9, 6.8)] and as accurate [81.6% (80.4, 82.7) versus 81.9% (80.7, 83.0)] as the CKD-EPI equation for young and middle-age adults; and less biased [-1.1 (-1.6, -0.6) versus 5.6 (5.1, 6.2)] and more accurate [86.1% (84.4, 87.7) versus 81.8% (79.7, 84.0)] than CKD-EPI for older adults.

CONCLUSIONS

The FAS equation has improved validity and continuity across the full age-spectrum and overcomes the problem of implausible eGFR changes in patients which would otherwise occur when switching between more age-specific equations.

Can the height-independent Pottel eGFR equation be used as a screening tool for chronic kidney disease in children?

Determination of plasma creatinine (Pcr) should be associated to an estimation of glomerular filtration rate (eGFR). Pottel et al. established a height-independent equation, eGFR = 107.3/(Pcr/Q) where Q is the median of Pcr (Pottel-Belgium). The aims were to 1) determine a local height-independent equation (Pottel-Lyon), 2) evaluate the performance of these equations compared to the Schwartz 2009 and Schwartz-Lyon equations, and 3) evaluate the height-independent equations in laboratory routine. Therefore, 1) all first pediatric Pcr determination (December 2009-June 2011) were collected, and median of Pcr was determined for each 1-year age interval (Q-Lyon), 2) GFR was measured (mGFR) in 359 children (438 measures) and compared to eGFR, and 3) all first Pcr determination (January 2012-June 2013) were used to calculate eGFR with the Pottel-Lyon and the Pottel-Belgium equations. Pcr was determined by an IDMS-standardized enzymatic assay. In the population with a mGFR, the Pottel-Lyon and the Schwartz-Lyon showed the best performance (bias, P10 and P30). However, the performance in identifying patients with a mGFR < 75 mL/min/1.73 m(2) was similar for all the studied equations.

CONCLUSION

The performance of the height-independent and dependent equations to identify mild renal dysfunction is similar. The height-independent Pottel equation could be proposed as an excellent screening tool for kidney disease when height information is not available. "

WHAT IS KNOWN

" • Determination of plasma creatinine in children is rarely associated to an estimation of glomerular filtration rate due to the lack of height information. • Pottel et al. developed a height-independent equation (eGFR = 107.3/(Pcr/Q) where Q is the median of Pcr for each age class. "

WHAT IS NEW

" • The performance of the height-independent (Pottel) or height-dependent (Schwartz) equations is similar to identify renal dysfunction (GFR < 75 mL/min/1.73 m (2) ) in children. • The height-independent Pottel equation could be an excellent screening tool for kidney disease in a general pediatric laboratory when height information is not available.

Accuracy of different equations in estimating GFR in pediatric kidney transplant recipients

BACKGROUND AND OBJECTIVE

The knowledge of renal function is crucial for the management of pediatric kidney transplant recipients. In this population, the most commonly used plasma creatinine (PCr)-based or cystatin C (CystC)-based GFR-predicting formulas may underperform (e.g., corticosteroids and trimethoprim may affect PCr concentration, whereas prednisone and calcineurin inhibitors may affect CystC concentration). This study evaluated the performance of six formulas in pediatric kidney transplant recipients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study used PCr-based formulas (bedside Schwartz, Schwartz-Lyon), CystC-based formulas (Hoek, Filler), and combined PCr-CystC-based formulas (CKD in Children [CKiD] 2012 and Zappitelli). The performance of these formulas was compared using inulin clearance as reference and assessed according to CKD stages in a historical cohort that included 73 pediatric kidney transplant recipients (199 measurements). The ability of the formulas to identify GFRs<60, <75, and <90 ml/min per 1.73 m(2) was assessed.

RESULTS

At measured GFR (mGFR) ≥90 ml/min per 1.73 m(2) (nine patients; 23 measurements), the Zappitelli formula had the highest 30% accuracy (P30) (95% [95% confidence interval (95% CI), 87% to 100%]) and the bedside Schwartz had the highest 10% accuracy (P10) (56% [95% CI, 32% to 72%]). At mGFR≥60 and <90 ml/min per 1.73 m(2) (22 patients; 91 measurements), all formulas had P30 values >80%. However, only the CKiD 2012 formula had a P10 value >50%. At mGFR<60 ml/min per 1.73 m(2) (42 patients; 85 measurements), the CKiD 2012 and Schwartz-Lyon formulas had the highest P10 (45% [95% CI, 34% to 55%] and 43% [95% CI, 33% to 54%]) and P30 (90% [95% CI, 84% to 97%] and 91% [95% CI, 86% to 98%]). All studied equations except Hoek and Filler had areas under the receiver-operating characteristic curves significantly >90% in discriminating patients with renal dysfunction at various CKD stages (GFR<60, <75, and <90 ml/min per 1.73 m(2)).

CONCLUSIONS

In pediatric kidney transplant recipients, the CKiD 2012 formula had the best performance at mGFRs<90 ml/min per 1.73 m(2). CystC-based formulas were not superior to PCr-based formulas.

Creatinine- versus cystatine C-based equations in assessing the renal function of candidates for liver transplantation with cirrhosis

Renal dysfunction is frequent in liver cirrhosis and is a strong prognostic predictor of orthotopic liver transplantation (OLT) outcome. Therefore, an accurate evaluation of the glomerular filtration rate (GFR) is crucial in pre-OLT patients. However, in these patients plasma creatinine (Pcr) is inaccurate and the place of serum cystatine C (CystC) is still debated. New GFR-predicting equations, based on standardized assays of Pcr and/or CystC, have been recently recommended in the general population but their performance in cirrhosis patients has been rarely studied. We evaluated the performance of the recently published Chronic Kidney Disease Epidemiology Collaboration equations (CKD-EPI-Pcr, CKD-EPI-CystC, and CKD-EPI-Pcr-CystC) and the more classical ones (4- and 6-variable MDRD and Hoek formulas) in cirrhosis patients referred for renal evaluation before OLT. Inulin clearance was performed in 202 consecutive patients together with the determination of Pcr and CystC with assays traceable to primary reference materials. The performance of the GFR-predicting equations was evaluated according to ascites severity (no, moderate, or refractory) and to hepatic and renal dysfunctions (MELD score  ≤ or >15 and KDOQI stages, respectively). In the whole population, CystC-based equations showed a better performance than Pcr-based ones (lower bias and higher 10% and 30% accuracies). CKD-EPI-CystC equation showed the best performance whatever the ascites severity and in presence of a significant renal dysfunction (GFR <60 mL/min/1.73 m(2)).

CONCLUSION

Pcr-based GFR predicting equations are not reliable in pre-OLT patients even when an IDMS-traceable enzymatic Pcr assay is used. Whenever a CystC-assay traceable to primary reference materials is performed and when a true measurement of GFR is not possible, CystC-based equations, especially CKD-EPI-CystC, may be recommended to evaluate renal function and for KDOQI staging.

A new equation to estimate the glomerular filtration rate in children, adolescents and young adults

BACKGROUND

A new estimated glomerular filtration rate (eGFR) equation, designed for isotope dilution mass spectrometry-standardized serum creatinine (Scr), is presented for use in children, adolescent boys and girls and young adults.

METHODS

The new equation, eGFR = 107.3/(Scr/Q), is based on the concept of normalized Scr: Q is the normalization value and is considered as the Scr concentration for the average healthy child, adolescent or young adult of a specific height (L) and is modeled as a height-dependent polynomial of the fourth degree.

RESULTS

The well-known Schwartz equation [eGFR = kL/Scr, k = 0.413 (Schwartz) or k = 0.373 (Schwartz-Lyon)] for children between 1 and 14 years can be seen as a special case of the new equation for which the Q-polynomial is simplified to a linear equation: Q = 0.0035 × L (cm). The new eGFR equation has been validated in a data set of n = 750 children, adolescents and young adults aged 10-25, against the true GFR (inulin method), and outperforms the selected (but most used) creatinine-based eGFR equations for children, mainly in the healthy GFR region.

CONCLUSIONS

The new Q(height)-eGFR equation serves as an excellent screening tool for kidney disease in 1-25-year-old children, adolescents and young adults.

Schwartz formula: is one k-coefficient adequate for all children?

BACKGROUND/OBJECTIVE

Plasma-creatinine-based equations to estimate the glomerular filtration rate are recommended by several clinical guidelines. In 2009, Schwartz et al. adapted the traditional Schwartz equation to children and adolescents but did not find different k-coefficients between children and adolescents (k = 36.5 for all patients). We reevaluated the coefficient of the 2009-Schwartz formula according to sex and age in a pediatric population.

PATIENTS/METHODS

We used linear mixed-effects models to reestimate the 2009-Schwartz k-coefficient in 360 consecutive French subjects aged 1 to 18 years referred to a single centre between July 2003 and July 2010 (965 measurements). We assessed the agreement between the estimated glomerular filtration rate obtained with the new formula (called Schwartz-Lyon) and the rate measured by inulin clearance. We then compared this agreement to the one between the measured glomerular filtration rate and 2009-Schwartz formula, first in the French then in a Swedish cohort.

RESULTS

In Schwartz-Lyon formula, k was estimated at 32.5 in boys <13 years and all girls and at 36.5 in boys aged ≥13 years. The performance of this formula was higher than that of 2009-Schwartz formula in children <13 years. This was first supported by a statistically significant reduction of the overestimation of the measured glomerular filtration rate in both cohorts, by better 10% and 30% accuracies, and by a better concordance correlation coefficient.

CONCLUSIONS

The performance and simplicity of Schwartz formula are strong arguments for its routine use in children and adolescents. The specific coefficient for children aged <13 years further improves this performance.

GFR estimation in adolescents and young adults

The performance of creatinine-based equations to obtain the estimated GFR in adolescents and young adults is poorly understood. We assessed creatinine-based GFR estimating equations in a cross-section of 751 adolescents and young adults (1054 measurements), using inulin clearance (measured GFR [mGFR]) as the reference method. We evaluated the following: Cockcroft-Gault, four-variable Modified Diet in Renal Disease, and the Chronic Kidney Disease Epidemiology Collaboration equations for adult participants, as well as the Schwartz 2009 and Schwartz-Lyon equations for pediatric age groups. Participants ranged in age from 10 to 26 years (mean 16.8 years); we divided the population into four groups according to age (10-12 years, 13-17 years, 18-21 years, and 21-25 years). Evaluation of the agreement between these formulas and mGFR (e.g., correlation, Bland-Altman plots, bias, and accuracy) showed that there was a good correlation between mGFR and both pediatric formulas in all age groups, whereas the adult formulas substantially overestimated mGFR. In conclusion, we recommend the use of pediatric equations to estimate GFR from childhood to early adulthood.

Assessing the antimicrobial prescription request process in a teaching hospital in Brazil: regulations and training

It is known that antimicrobials are often prescribed inappropriately. One method used to deal with this problem is to regulate antimicrobial use by monitoring prescriptions. We report a study of physician compliance with the request for antibiotic process which was prepared and reviewed by a special infection control committee in our hospital the Nosocomial Infection Prevention Service (SCIH). The objective of this study was to identify the profile of inappropriate requests for restricted therapeutic antimicrobials used at Nossa Senhora da Conceição Hospital (HNSC), in Porto Alegre, Brazil. All 3,389 requests for therapeutic antimicrobials made between May 20, and October 31, 1996, were assessed and classified as appropriate and inappropriate. We determined that 17. 8% of the requests were inappropriate (a total of 720 errors). These were categorized according to 12 reasons for inappropriateness. Of these, the 3 most frequent inappropriate requests were deviation from standard use (26.73%), inappropriate length of treatment (23. 19%), and unfounded justification (13.61%). The reasons for inappropriateness were also arranged in three categories considering the following aspects: I. technical (59%); II. compatibility with the institutional program (32.36%), and III. administrative (8.61%). The 720 requests that were initially rejected were evaluated to see how antibiotic use was affected. In approximately 400 (55%), the forms could be appropriately modified after discussion with the physician. We conclude from this study that most of the inappropriate requests for antimicrobials in our hospital can be remedied by educating the staff since the errors were largely technical in nature. Thus, the SCIH should focus more on its role as an educational rather than as a regulatory body. By expanding this educational role, we anticipate improved physician compliance with our guidelines, and more appropriate antimicrobial prescribing and usage.