Evaluation of serum creatinine concentration-based glomerular filtration rate equations in pediatric patients with chronic kidney disease

Improved equations to estimate GFR in Chinese children with chronic kidney disease

BACKGROUND

There is currently no specific equation for estimating glomerular filtration rate (GFR) in Chinese children with chronic kidney disease (CKD). The commonly used equations are less robust than expected; we therefore sought to derive more appropriate equations for GFR estimation.

METHODS

A total of 751 Chinese children with CKD were divided into 2 groups, training group (n = 501) and validation group (n = 250). In the training group, a univariate linear regression model was used to calculate predictability of variables associated with GFR. Residuals were compared to determine multivariate predictability of GFR in the equation. Standard regression techniques for Gaussian data were used to determine coefficients of GFR-estimating equations after logarithmic transformation of measured GFR (iGFR), height/serum creatinine (height/Scr), cystatin C, blood urea nitrogen (BUN), and height. These were compared with other well-known equations using the validation group.

RESULTS

Median ^99mTc-DTPA GFR was 90.1 (interquartile range: 67.3-108.6) mL/min/1.73 m² in training dataset. Our CKD equation, eGFR (mL/min/1.73 m²) = 91.021 [height(m)/Scr(mg/dL)/2.7]^0.443 [1.2/Cystatin C(mg/L)]^0.335 [13.7/BUN (mg/dL)]^-0.095 [ 0.991^male] [height(m)/1.4]^0.275, was derived. This was further tested in the validation group, with percentages of eGFR values within 30% and 15% of iGFR (P30 and P15) of 76.00% and 48.40%, respectively. For centres with no access to cystatin C, a creatinine-based equation, eGFR (mL/min/1.73 m²) = 89.674 [height(m)/Scr(mg/dL)/2.7]^0.579 [ 1.007^male] [height(m)/1.4]^0.187, was derived, with P30 and P15 73.60% and 49.20%, respectively. These were significantly higher compared to other well-known equations (p < 0.05).

CONCLUSION

We developed equations for GFR estimation in Chinese children with CKD based on Scr, BUN and cystatin C. These are more accurate than commonly used equations in this population.

Estimated glomerular filtration rate in children: adapting existing equations for a specific population

BACKGROUND

Creatinine-based glomerular filtration rate (GFR)-estimating equations frequently do not perform well in populations that differ from the development populations in terms of mean GFR, age, pathology, ethnicity, and diet. After first evaluating the performance of existing equations, the aim of this study was to demonstrate the utility of an in-house modification of the equations to better fit a specific population.

METHODS

Estimated GFR using 8 creatinine-based equations was first compared to 2-sample ⁵¹Cr-ethylenediaminetetra-acetic acid plasma clearance in non-cancer and cancer groups independently. The groups were then divided into development and validation sets. Using the development set data, the Microsoft® Excel SOLVER add-in was used to modify the parameters of 7 equations to better fit the data. Using the validation set data, the performance of the original and modified equations was compared.

RESULTS

Two hundred fifty-six GFR measurements were performed in 160 children. GFR was overestimated in both groups (non-cancer 4.3-22.6 ml/min/1.73 m², cancer 17.2-46.6 ml/min/1.73 m²). The root mean square error (RMSE) was 19.1-21.8 ml/min/1.73 m² (non-cancer) and 18.6-20.8 ml/min/1.73 m² (cancer). The P₃₀ values were 49.1-73.0% (non-cancer) and 19.6-66.0% (cancer). Modifying the parameters of seven equations resulted in significant improvements in the P₃₀ values in the non-cancer (65.0-85.0%) and cancer (79.6-87.8%) groups.

CONCLUSIONS

Modifying the parameters of pediatric GFR estimating-equations using a simple Excel-based tool significantly improved their accuracy in both non-cancer and cancer populations. Graphical abstract.

Full age spectrum equation versus CKD-EPI and MDRD equations to estimate glomerular filtration rate in adults with obstructive nephropathy

Objective

To compare the full age spectrum (FAS) equation with the Modification of Diet in Renal Disease (MDRD) and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations in predicting glomerular filtration rate (GFR) in patients with obstructive nephropathy.

Methods

Adult patients with obstructive nephropathy who had undergone a GFR measurement using technetium-99m diethylenetriaminepentaacetic acid radioisotope renography were enrolled in the study. The measured GFR was taken as the reference value. Bias, precision and accuracy were compared between the three equations. Kappa test and the Bland–Altman method were used to evaluate the classification and the agreement. Receiver operating characteristic (ROC) curve analysis was used to describe the diagnostic accuracy of each equation.

Results

A total of 327 patients were enrolled. The P30 value for the FAS equation was 60.2% in the overall study cohort. The FAS equation had the highest diagnostic accuracy (ROC^AUC = 0.87, 95% confidence interval [CI] 0.84, 0.91) compared with the MDRD equation (ROC^AUC = 0.86, 95% CI 0.82, 0.89). The median bias of the FAS equation was significantly higher than that of the MDRD equation (8.7 versus 7.6 ml/min/1.73 m², respectively).

Conclusions

Despite the drawbacks associated with each equation, the FAS equation was probably closer to ideal to estimate GFR in patients with obstructive nephropathy.

Recommendations for urological follow-up of patients with neurogenic bladder secondary to spinal cord injury

PURPOSE

To review currently available guidelines and recommendations regarding urological follow-up of patients after spinal cord injury (SCI) and present an evidence-based summary to support clinicians in their clinical practice.

METHODS

Maximum data were collected according to different methods, including searches with multiple and specific keywords, reference checks, gray literature searches (congress reports, working papers, statement documents), and browsing-related Web site access. Obtained data were analyzed with the modified version of the Oxford grading system for recommendations using levels of evidence (LE) and grades of recommendation (GR).

RESULTS

Different surveillance strategies exist, but there is no consensus among authors and organizations. As a result, practice patterns vary around the world. The present review indicates that proper urological follow-up of SCI patients should consist of medical history (LE 1-4, GR B-C), clinical examination (LE 4, GR C), renal laboratory tests (LE 1-3, GR B), imaging surveillance of the upper urinary tract (LE 1-3, GR A-B), urodynamic study (LE 2-4, GR B-C), and cystoscopy/cytology (LE 1-4, GR D). Clinicians agree that SCI patients should be followed up regularly with an individually tailored approach. A 1-year follow-up schedule seems reasonable in SCI patients without additional risk factors of renal deterioration (LE 3-4, GR C). In those who manifest risk factors, report changes in bladder behavior, or present with already developed complications of neurogenic bladder dysfunction, follow-up plans should be modified with more frequent checkups (LE 4, GR C). Urodynamic study should be repeated and considered as a routine monitoring strategy.

CONCLUSION

Individuals with neurogenic lower urinary tract dysfunction are at increased risk of multiple complications. Nevertheless, proper follow-up after SCI improves the prognosis for these patients and their quality of life.

The new Asian modified CKD-EPI equation leads to more accurate GFR estimation in Chinese patients with CKD

OBJECTIVE

To verify whether the new Asian modified CKD-EPI equation improved the performance of original one in determining GFR in Chinese patients with CKD.

METHOD

A well-designed paired cohort was set up. Measured GFR (mGFR) was the result of ^99mTc-diethylene triamine pentaacetic acid (^99mTc-DTPA) dual plasma sample clearance method. The estimated GFR (eGFR) was the result of the CKD-EPI equation (eGFR1) and the new Asian modified CKD-EPI equation (eGFR2). The comparisons were performed to evaluate the superiority of the eGFR2 in bias, accuracy, precision, concordance correlation coefficient and the slope of regression equation and measure agreement.

RESULTS

A total of 195 patients were enrolled and analyzed. The new Asian modified CKD-EPI equation improved the performance of the original one in bias and accuracy. However, nearly identical performance was observed in the respect of precision, concordance correlation coefficient, slope of eGFR against mGFR and 95 % limit of agreement. In the subgroup of GFR < 60 mL min^-1/1.73 m², the bias of eGFR1 was less than eGFR2 but they have comparable precision and accuracy. In the subgroup of GFR > 60 mL min^-1/1.73 m², eGFR2 performed better than eGFR1 in terms of bias and accuracy.

CONCLUSION

The new Asian modified CKD-EPI equation can lead to more accurate GFR estimation in Chinese patients with CKD in general practice, especially in the higher GFR group.

The new Asian modified CKD-EPI equation leads to more accurate GFR estimation in Chinese patients with CKD

OBJECTIVE

To verify whether the new Asian modified CKD-EPI equation improved the performance of original one in determining GFR in Chinese patients with CKD.

METHOD

A well-designed paired cohort was set up. Measured GFR (mGFR) was the result of ^99mTc-diethylene triamine pentaacetic acid (^99mTc-DTPA) dual plasma sample clearance method. The estimated GFR (eGFR) was the result of the CKD-EPI equation (eGFR1) and the new Asian modified CKD-EPI equation (eGFR2). The comparisons were performed to evaluate the superiority of the eGFR2 in bias, accuracy, precision, concordance correlation coefficient and the slope of regression equation and measure agreement.

RESULTS

A total of 195 patients were enrolled and analyzed. The new Asian modified CKD-EPI equation improved the performance of the original one in bias and accuracy. However, nearly identical performance was observed in the respect of precision, concordance correlation coefficient, slope of eGFR against mGFR and 95 % limit of agreement. In the subgroup of GFR < 60 mL min^-1/1.73 m², the bias of eGFR1 was less than eGFR2 but they have comparable precision and accuracy. In the subgroup of GFR > 60 mL min^-1/1.73 m², eGFR2 performed better than eGFR1 in terms of bias and accuracy.

CONCLUSION

The new Asian modified CKD-EPI equation can lead to more accurate GFR estimation in Chinese patients with CKD in general practice, especially in the higher GFR group.

Applicability of the Schwartz Equation and the Chronic Kidney Disease in Children Bedside Equation for Estimating Glomerular Filtration Rate in Overweight Children

STUDY OBJECTIVE

To determine if significant correlations exist between glomerular filtration rate (GFR) prediction equation values, derived by using the original Schwartz equation and the Chronic Kidney Disease in Children (CKiD) bedside equation with a 24-hour urine creatinine clearance (Clcr ) value normalized to a body surface area of 1.73 m(2) in overweight and obese children.

DESIGN

Prospective analysis (20 patients) and retrospective analysis (43 patients).

SETTING

Pediatric inpatient ward and pediatric nephrology clinic at a comprehensive academic medical center.

PATIENTS

Sixty-three pediatric patients (aged 5-17 years), of whom 27 were overweight (body mass index [BMI] at the 85th percentile or higher) and 36 were not overweight (BMI lower than the 85th percentile [controls]) between 2007 and 2012.

METHODS AND MAIN RESULTS

Data from the overweight patients were compared with nonoverweight controls. GFR values were calculated by using the original Schwartz equation and the CKiD bedside equation. Each patient's 24-hour urine Clcr value normalized to a body surface area of 1.73 m(2) served as the index value. A Pearson correlation coefficient model was used to determine association between the 24-hour urine Clcr value (index value) with the Schwartz and CKiD GFR estimations. Significant correlation was found to exist between the Schwartz and CKiD bedside GFR estimations relative to the 24-hour urine Clcr in the control subjects (r = 0.85, p<0.0001, and r = 0.85, p<0.0001, respectively). Significant correlation was also found to exist between the Schwartz and CKiD bedside GFR values with the 24-hour urine Clcr value in overweight subjects (r = 0.86, p<0.0001, and r = 0.86, p<0.0001, respectively). The Schwartz equation estimated average GFR 21.75 ml/minute/1.73 m(2) higher than 24-hour urine Clcr (p<0.0001) in overweight children with a kidney disorder. The CKiD bedside GFR estimations were not significantly different compared with 24-hour urine Clcr values for the overweight group with kidney disorder (p=0.85).

CONCLUSION

The Schwartz and CKiD bedside estimations of GFR correlated with 24-hour urine Clcr values in both overweight and nonoverweight children. Compared with the Schwartz equation, which tended to overestimate renal function, the CKiD bedside equation appeared to approximate 24-hour urine Clcr more closely in overweight children with kidney disorder.

Effect of Kidney Function on Drug Kinetics and Dosing in Neonates, Infants, and Children

Neonates, infants, and children differ from adults in many aspects, not just in age, weight, and body composition. Growth, maturation and environmental factors affect drug kinetics, response and dosing in pediatric patients. Almost 80% of drugs have not been studied in children, and dosing of these drugs is derived from adult doses by adjusting for body weight/size. As developmental and maturational changes are complex processes, such simplified methods may result in subtherapeutic effects or adverse events. Kidney function is impaired during the first 2 years of life as a result of normal growth and development. Reduced kidney function during childhood has an impact not only on renal clearance but also on absorption, distribution, metabolism and nonrenal clearance of drugs. 'Omics'-based technologies, such as proteomics and metabolomics, can be leveraged to uncover novel markers for kidney function during normal development, acute kidney injury, and chronic diseases. Pharmacometric modeling and simulation can be applied to simplify the design of pediatric investigations, characterize the effects of kidney function on drug exposure and response, and fine-tune dosing in pediatric patients, especially in those with impaired kidney function. One case study of amikacin dosing in neonates with reduced kidney function is presented. Collaborative efforts between clinicians and scientists in academia, industry, and regulatory agencies are required to evaluate new renal biomarkers, collect and share prospective pharmacokinetic, genetic and clinical data, build integrated pharmacometric models for key drugs, optimize and standardize dosing strategies, develop bedside decision tools, and enhance labels of drugs utilized in neonates, infants, and children.

Applicability of various estimation formulas to assess renal function in Chinese children

BACKGROUND

This study was to evaluate the relative applicability of the most commonly used estimation formulas for renal glomerular filtration rate (GFR) of Chinese children with chronic kidney disease (CKD).

METHODS

One hundred CKD patients of less than 17 years old were divided into two groups by sex which was further categorized into five subgroups based on CKD staging according to the "reference" GFR (rGFR) determined by Tc-99m-DTPA renal dynamic imaging. Four GFR markers including serum cystatin C (CysC), β2-microglobulin, creatinine, and blood urea nitrogen were measured.

RESULTS

Among all four markers, CysC best reflected the extent of glomerular damages for CKD stage 1. The value for estimation of GFR (eGFR) was derived from five different formulas either over-estimated or underestimated GFR as referenced to rGFR, and the extent of deviations was dependent on gender, age and CKD stage. The Counahan-Barratt formula and the Schwartz formula gave the most accurate estimations of GFR for CKD stages 1 and 2-3, respectively regardless of gender and age differences. Receiver operating characteristic analyses indicated that the Counahan-Barratt formula has the highest diagnostic accuracy.

CONCLUSION

The Counahan-Barratt formula provides the best approximation to rGFR, thereby the highest applicability to Chinese children with CKD of different genders, ages and CKD stages.

Value of serum cystatin C in estimating renal function in children with non-renal solid organ transplantation

Children with non-renal solid organ transplants are surviving longer, but outcome is complicated by CKD. Accurate and frequent renal function monitoring is imperative to recognize and institute measures early to reverse, prevent, or arrest progression. This study of 59 children determined the accuracy (P30), bias, sensitivity and specificity between measured renal function by NM-GFR, and estimated GFR by three formulas: Filler (serum cystatin C), mSchwartz (serum creatinine), and CKiD (serum cystatin C, creatinine, urea, and height). Mean GFR by all formulas differed significantly from NM-GFR. Filler and mSchwartz formulas significantly increased the proportion of patients with GFR ≥ 90 mL/min/1.73 m(2) (CKD stage 1) while decreasing those with GFR 60-89 mL/min/1.73 m(2) (CKD stage 2). All formulas overestimated GFR. CKiD showed the highest P30 and lowest bias (79.7%; 6.9 mL/min/1.73 m(2) ) followed by Filler (67.7%; 19.9 mL/min/1.73 m(2) ) and Schwartz (57.6%; 26.8 mL/min/1.73 m(2) ) for all GFR values. All formulas performed best with GFR ≥ 90 mL/min/1.73 m(2) , but CKiD was the only formula to achieve 91.1% accuracy. All formulas showed high sensitivities, but low specificities at NM-GFR cutoff at 90. Thus, GFR estimated by CKiD followed by Filler formula is an adequate method to monitor renal function closely and frequently in these children.

Agreement among measurements and estimations of glomerular filtration in children with cancer

BACKGROUND

Glomerular filtration is an important route of elimination for many types of chemotherapy. Accurate estimation of glomerular filtration at the bedside is essential in the management of children with cancer. Bedside formulae for the estimation of glomerular filtration have not been validated in children with cancer. We investigated the accuracy of three formulae (the original Schwartz, Counahan-Barratt, and revised Schwartz equations) against measurement of the glomerular filtration rate (GFR) in a cohort of children with cancer.

PROCEDURE

This was a retrospective review of existing data from a single institution. The electronic medical record was queried for subjects meeting inclusion criteria during a 3.5 year time frame. Bland-Altman analyses were used to assess agreement among current formulae and estimating the GFR compared to the measured, or index GFR. Logistic regression was performed to identify potential variables with an effect on the estimation of GFR.

RESULTS

None of the three estimation formulae provided a reliable estimate of the index GFR. The mean difference was lowest between the revised Schwartz and the index GFR compared to the other two formulae and the index GFR. For the original Schwartz equation, age and prior receipt of chemotherapy were significant predictors of under- and overestimation. For the revised Schwartz equation, one age group (6-12 years) and a diagnosis of neuroblastoma actively receiving chemotherapy were positive risk factors for overestimation of the GFR.

CONCLUSION

Currently available estimation formulae for GFR may not be appropriate for children with cancer.

Cystatin C as a marker of early renal insufficiency in children with congenital neuropathic bladder

PURPOSE

Due to decreased muscle mass in children with congenital neuropathic bladder there may be significant inaccuracy when using the creatinine based estimated glomerular filtration rate. Cystatin C is highly sensitive and specific for measuring changes in the glomerular filtration rate in children and in patients with muscle wasting conditions. We hypothesized that a cystatin C calculated glomerular filtration rate would be more sensitive than the standard creatinine based modified Schwartz equation to detect renal insufficiency in children with congenital neuropathic bladder.

MATERIALS AND METHODS

We prospectively identified children with congenital neuropathic bladder at a multidisciplinary spina bifida clinic who underwent serum creatinine and serum cystatin C testing. Clinical history and anthropomorphic variables at the time of laboratory testing were catalogued. The creatinine based glomerular filtration rate was estimated using the modified (bedside) Schwartz formula and the cystatin C based rate was calculated using the Zappitelli cystatin C formula.

RESULTS

Dual estimated glomerular filtration rate calculation was done in 69 children at a total of 74 patient encounters. Absolute creatinine was within age range normal limits in each patient, including 1 with chronic kidney disease stage 3A. The median creatinine based estimated glomerular filtration rate was 123 ml per minute/1.73 m(2) (range 58 to 229). The median cystatin C based estimated rate was 103 ml per minute/1.73 m(2) (range 47 to 144) for an absolute median rate reduction of 15.4%. Using cystatin C estimates chronic kidney disease stage was upgraded from stage 1 to 2 in 13 patients (18.8%).

CONCLUSIONS

In children with neuropathic bladder the cystatin C estimated glomerular filtration rate is a better screening test for early renal insufficiency that is not detected by creatinine based rate calculations. To our knowledge it remains to be determined whether the cystatin C estimated glomerular filtration rate can ultimately improve the clinical outcome in this population.

Glomerular Filtration Rate Equations Do Not Accurately Predict Vancomycin Trough Concentrations in Pediatric Patients

Background: The Bedside Chronic Kidney Disease in Children (CKiD) equation was developed using data from children with chronic kidney disease. Some institutions are using this equation in all pediatric patients, regardless of renal function, to adjust medications. No data have shown that the Bedside CKiD equation is equivalent or better than the Schwartz equation in estimating glomerular filtration rate (GFR) in pediatric patients with normal renal function. Objective: To compare GFR estimates using the Bedside CKiD and Schwartz equations and determine if either offers sufficient vancomycin dosing guidance in hospitalized pediatric patients. Methods: This retrospective review at a single-center, academic, pediatric hospital included patients 2 to 12 years old with a steady-state vancomycin trough collected between January 1, 2010 and December 31, 2011. Patients with acute kidney injury or lacking essential data (e.g., height and serum creatinine), were excluded. An estimated GFR (eGFR) was calculated using the Schwartz and Bedside CKiD equations. Pearson correlations and linear regressions compared the eGFR values and vancomycin troughs. Results: A total of 50 vancomycin troughs were analyzed. There was a weak relationship between the eGFR and troughs for the Schwartz equation ( r2 = 0.028) and Bedside CKiD equation ( r2 = 0.028). A weak relationship between serum creatinine and troughs was observed ( r2 = 0.132). Limitations include small sample size and retrospective design. Conclusions: Neither equation correlates well with vancomycin troughs, suggesting that therapeutic monitoring remains important. Better GFR estimation methods are needed in pediatrics to aid appropriate dosing of renally eliminated medications.

Kidney function and tobacco smoke exposure in US adolescents

BACKGROUND AND OBJECTIVE

Active smoking and secondhand smoke (SHS) are known risk factors for kidney disease in adults. We evaluated the association between exposure to active smoking or SHS and kidney function in US adolescents.

METHODS

This is a cross-sectional study in 7516 adolescents aged 12-17 who participated in NHANES 1999-2010 and had serum creatinine and cotinine measures. Active smoking was defined as self-reported smoking or serum cotinine concentrations >10 ng/mL. SHS was defined as nonactive smokers who self-reported living with ≥1 smokers or serum cotinine concentrations ≥ 0.05 ng/mL. Kidney function was determined by using the chronic kidney disease in children estimated glomerular filtration rate (eGFR) equation.

RESULTS

Median (interquartile range) eGFR and serum cotinine concentrations were 96.8 (85.4-109.0) mL/minute per 1.73 m(2) and 0.07 (0.03-0.59) ng/mL, respectively. After multivariable adjustment, eGFR decreased 1.1 mL/minute per 1.73 m(2) (95% confidence interval [CI]: -1.8 to -0.3) per interquartile range increase in serum cotinine concentrations. The mean (95%CI) difference in eGFR for serum cotinine tertiles 1, 2, and 3 among children exposed to SHS compared to unexposed were -0.4 (-1.9 to 1.2), -0.9 (-2.7 to 0.9), and -2.2 (-4.0 to -0.4) mL/minute per 1.73 m(2), respectively (P = .03). The corresponding values among tertiles of active smokers compared to unexposed were 0.2 (-2.2 to 2.6), -1.9 (-3.8 to 0.0), and -2.6 (-4.6 to -0.6) mL/minute per 1.73 m(2) (P = .01).

CONCLUSIONS

Tobacco smoke exposure was associated with decreased eGFR in US adolescents, supporting the possibility that tobacco smoke effects on kidney function begin in childhood.