Comparison of two formulae for estimation of glomerular filtration rate in children

Population Pharmacokinetics of Milrinone in Infants, Children, and Adolescents

Milrinone is a type 3 phosphodiesterase inhibitor used to improve cardiac output in critically ill infants and children. Milrinone is primarily excreted unchanged in the urine, raising concerns for toxic accumulation in the setting of renal dysfunction of critical illness. We developed a population pharmacokinetic model of milrinone using nonlinear mixed-effects modeling in NONMEM to perform dose-exposure simulations in children with variable renal function. We included children aged <21 years who received intravenous milrinone per clinical care. Plasma milrinone concentrations were measured using a validated liquid chromatography-tandem mass spectrometry assay (range 1-5000 ng/mL). We performed dose-exposure simulations targeting steady-state therapeutic concentrations of 100-300 ng/mL previously established in adults and children with cardiac dysfunction. We simulated concentrations over 48 hours in typical subjects with decreasing creatinine clearance (CrCl), estimated using the updated bedside Schwartz equation. Seventy-four patients contributed 111 plasma samples (concentration range, 4-634 ng/mL). The median (range) postmenstrual age (PMA) was 3.7 years (0-18), and median weight (WT) was 13.1 kg (2.6-157.7). The median serum creatinine and CrCl were 0.5 mg/dL (0.1-3.1) and 117.2 mL/min/1.73 m2 (13.1-261.3), respectively. A 1-compartment model characterized the pharmacokinetic data well. The final model parameterization was: Clearance (L/h) = 15.9*(WT [kg] / 70)0.75 * (PMA1.12 / (67.71.12 +PMA1.12 )*(CrCl / 117)0.522 ; and Volume of Distribution (L) = 32.2*(WT [kg] / 70). A loading dose of 50 µg/kg followed by a continuous infusion of 0.5 µg/kg/min resulted in therapeutic concentrations, except when CrCl was severely impaired at ≤30 mL/min/1.73 m2 . In this setting, a 25 µg/kg loading dose and 0.25 µg/kg/min continuous infusion resulted in therapeutic exposures.

Comparison of three formulae for estimation of glomerular filtration rate in severely malnourished children at tertiary care facility

Objectives

First objective was to compare eGFR by Updated Schwartz (US) and Simple Height Independent (SHID) formula with Original Schwartz (OS) in children with Severe Acute Malnutrition (SAM). The second objective was to compare eGFR in children below and above two years.

Methods

This analytic study on estimation of GFR was based on retrospective data collected from 78 children with SAM at Nutritional Rehabilitation Unit from October 2014 - March 2015. Glomerular filtration rate was calculated using serum creatinine (S. Cr) and height in Original Schwartz, US and by age in SHID equation and compared with OS as standard. Data was analyzed using descriptive statistics.

Results

There were 78 children in this study. Males were 39(50%). Mean age of patients was 18±15.53 months with 62(79.48%) ≤24 months. Mean weight, height and Mid Upper Arm Cir-cumference was 5.69±2.42kg, 68.52+13.59 cm and 10±1.57 cm respectively. Mean eGFR by OS, US and SHID formula was 71.45±49.89, 58.06±3.91 and 59.33±3.73ml/min/1.73m2 respectively. There was significant difference (0.001) in mean eGFR calculated by three different formulae. Majority of children (73%) had subnormal GFR (<90 ml/min /1.73 m2). There was a significant difference in GFR ≥90ml calculated by US compared to OS (0.025) and by SHID with OS (0.04) in children below two years and no difference in children above two years. But there was no difference in other categories of eGFR calculated by either of formula in both age groups.

Conclusion

We found a significant difference in eGFR in ranges above 90 ml/min/1.73 m2 by US compared to OS as well as by SHID with OS in children below two years and no difference in children above two years. Also, there was no difference in GFR categories below 90 ml/min /1.73 m2 calculated by either of formula in both age groups. So, we may conclude that either of formula can be used in clinical practice for eGFR in mild to severe renal dysfunction in severely malnour-ished children.

Updated height- and creatinine-based equation and its validation for estimation of glomerular filtration rate in children from developing countries

BACKGROUND

Since the original Schwartz formula overestimates glomerular filtration rate (GFR), it is proposed that the constant (k) that accounts for the method of creatinine estimation be derived locally. We derived a new k for height (cm)/serum creatinine (mg/dl) (ht/scr) equation by regression analysis.

METHODS

In a cross-sectional observational study, 197 children (2-18 years) with chronic kidney disease (CKD), who underwent reference GFR measurement by plasma clearance of diethylenetriamine pentaacetic acid (dGFR) at a tertiary care hospital, formed the index dataset for deriving the prediction equations for estimating GFR. Serum creatinine was estimated by the kinetic Jaffe method. The prediction equations were validated on a separate cohort of 225 children with CKD.

RESULTS

The median creatinine was 0.7 mg/dl and dGFR was 80.5 (interquartile range 18.1-137.5) ml/min/1.73 m(2). The new k (regression coefficient of height/creatinine) was 0.42 (R(2) = 0.61) and the updated equation was GFR = 0.42 × (ht/scr). Addition of age and mid-arm circumference (MAC) to this equation improved R (2) to 62.3%. Based on the above parameters, the new equation for estimating GFR was GFR (ml/min/1.73 m(2)) = 0.257 × [ht/scr](0.95) × [age (year)](-0.19) × [MAC (cm)](0.397). The two equations performed comparably, with a mean bias <2 ml/min/1.73 m(2). The updated ht/scr equation yielded 74% and 24% estimated GFR values that were within 30% and 10% of the measured dGFR, respectively.

CONCLUSIONS

The updated equation, with a k value of 0.42, provides a reasonably accurate bedside estimate of GFR in children in countries where creatinine is estimated by the kinetic Jaffe method.

Predictors and consequences of higher estimated glomerular filtration rate at dialysis initiation

There have been no studies in pediatric dialysis patients to evaluate the impact of higher estimated glomerular filtration rate (eGFR) at dialysis initiation on clinical outcomes. Baseline clinical and demographic information was collected for children aged 1-18 years undergoing incident dialysis from 1995-2002 within the United States Renal Data System. Baseline eGFRs calculated by the Schwartz formula were categorized as high (>15 ml/min/1.73 m(2)) or low (< or = 15 ml/min/1.73 m(2)). We determined predictors of eGFR at baseline, and associations between baseline eGFR and subsequent hospitalization for hypertension (HTN) or pulmonary edema (PE) in a longitudinal nonconcurrent pediatric end-stage renal disease (ESRD) cohort. Twenty percent of children had a high eGFR at initiation. Black children were less likely to initiate dialysis with a high eGFR [adjusted odds ratio (adjOR) 0.71, p < 0.001]. Girls were less likely to have a high eGFR at baseline (adjOR 0.71, p < 0.001). Children who received predialysis erythropoietin therapy were more likely to start dialysis with a high eGFR (adjOR 6.67, p < 0.001). Children with higher baseline eGFR were found to have a 21% decreased risk of hospitalization [adjusted hazard ratio (HR) 0.79, 95% confidence interval (CI) 0.65-0.96, p = 0.02]. It is not known whether this clinical benefit will result in decreased mortality and complication rates from cardiovascular disease.

On the relationship between glomerular filtration rate and serum creatinine in children

The Schwartz formula (eGFR = kL/Scr, with k = 0.55) to determine the estimated glomerular filtration rate (eGFR) in children with chronic kidney disease (CKD), based on length (L) and serum creatinine (Scr) has recently been updated for enzymatic serum creatinine concentrations, resulting in k = 0.413. Based on a meta-analysis, we evaluated the validity of this updated equation and other published equations for healthy children. This is the first time that publicly available data for healthy children of uncorrected and body surface area (BSA)-corrected median GFR have been combined with median serum creatinine values and median lengths and weights from different sources in the literature to evaluate several statistical models to estimate GFR in children. For enzymatic serum creatinine, we show that the simple model for uncorrected GFR (uGFR = k'L(3)/Scr, with k' = 1.32 x 10(-5)) and the BSA-corrected GFR (cGFR = kL/Scr, analogous to the Schwartz formula), with an important age-dependent adaptation for k (k = 0.0414 x 1n (Age) + 0.3018), correlate extremely well with chromium-51-ethylenediamine tetra-acetic acid ((51)Cr-EDTA) data for children between 1 month and 14 years of age. With this age-dependent modification for k, presented here, the simple bedside calculation tool derived by Schwartz can be used for screening all children for CKD. When height information is not available, the Lund-Malmö equation is an excellent alternative.

Renal impairment in children with cystic fibrosis

BACKGROUND

Due to the improvement in life expectancy in cystic fibrosis (CF), co-morbidities such as renal function impairment may be more frequent.

AIM

To determine the prevalence of renal disease in children with CF and to identify associated risk factors.

METHODS

A single-center retrospective study analyzing the genetic, clinical and therapeutic characteristics of 112 children. The estimated glomerular filtration rate (GFR), microalbuminuria and lithiasic risk factors were assessed.

RESULTS

The median calculated GFR (Schwartz) was 123, 161 and 155ml/min/1.73m(2) in children aged 1, 6 and 15years, respectively. The cumulative dose of aminoglycosides was not correlated to GFR. Microalbuminuria was present in 22/38 patients. Hyperoxaluria was observed in 58/83 patients and was associated with a severe genotype, pancreas insufficiency and liver disease. Hypercalciuria, hyperuricuria and hypocitraturia were identified in 16/87, 15/83 and 57/76 patients, respectively.

CONCLUSION

Renal impairment in CF has various presentations. There appears to be low levels of renal impairment in children with CF. However, the risk of oxalocalcic urolithiasis is enhanced, and GFR may be underestimated by the Schwartz formula. Further studies using measured GFR techniques are thus warranted.

The Lund-Malmö creatinine-based glomerular filtration rate prediction equation for adults also performs well in children

OBJECTIVE

To evaluate the clinical performance in a paediatric population of the Lund-Malmö creatinine-based glomerular filtration rate (GFR) prediction equations, primarily developed for adults.

MATERIAL AND METHOD

Iohexol clearance was used as the gold standard in 85 paediatric Caucasian patients (0.3-17 years; 37 F/48 M). One Lund-Malmö equation was based on age and gender (LM) and one included lean body mass (LM-LBM). Comparisons focused on correlation (adjusted R2), bias (median percent error) and accuracy (proportions of predicted GFR differing < or = 30% from measured GFR) (mL/min/1.73 m2). The performances were compared with those of the Modification of Diet in Renal Disease (MDRD) Study equation, a dedicated paediatric creatinine equation, Counahan-Barratt (CB) and a cystatin C-based equation.

RESULTS

The MDRD equation performed poorly with a median bias of 96%. Of the remaining equations, only the LM-LBM produced significant bias (+10% in median) according to line of identity regression analysis. The LM equation yielded marginally higher accuracy (76%) than the LM-LBM equation (74%) and the CB (73%), but lower than the cystatin C-based equation (82%). However, the estimated accuracy figures for these four equations were generally imprecise and none of the differences compared with the LM equation was statistically significant.

CONCLUSION

In contrast to most creatinine-based GFR prediction equations, the LM equation performs adequately for both children and adults. This may be due to the unique model-building principles used when the LM equation was established. Further validation in a larger paediatric population is necessary.

New equations to estimate GFR in children with CKD

The Schwartz formula was devised in the mid-1970s to estimate GFR in children. Recent data suggest that this formula currently overestimates GFR as measured by plasma disappearance of iohexol, likely a result of a change in methods used to measure creatinine. Here, we developed equations to estimate GFR using data from the baseline visits of 349 children (aged 1 to 16 yr) in the Chronic Kidney Disease in Children (CKiD) cohort. Median iohexol-GFR (iGFR) was 41.3 ml/min per 1.73 m(2) (interquartile range 32.0 to 51.7), and median serum creatinine was 1.3 mg/dl. We performed linear regression analyses assessing precision, goodness of fit, and accuracy to develop improvements in the GFR estimating formula, which was based on height, serum creatinine, cystatin C, blood urea nitrogen, and gender. The best equation was: GFR(ml/min per 1.73 m(2))=39.1[height (m)/Scr (mg/dl)](0.516) x [1.8/cystatin C (mg/L)](0.294)[30/BUN (mg/dl)](0.169)[1.099](male)[height (m)/1.4](0.188). This formula yielded 87.7% of estimated GFR within 30% of the iGFR, and 45.6% within 10%. In a test set of 168 CKiD patients at 1 yr of follow-up, this formula compared favorably with previously published estimating equations for children. Furthermore, with height measured in cm, a bedside calculation of 0.413*(height/serum creatinine), provides a good approximation to the estimated GFR formula. Additional studies of children with higher GFR are needed to validate these formulas for use in screening all children for CKD.

Solitary kidney

The study provides the pediatric practitioner with a tool to determine whether the child with an apparently normal solitary kidney requires an in-depth investigation. Medical records from January 1, 1995 to December 31, 2006 identified 96 children with solitary kidneys and showed 78 with a normal appearing, hypertrophied solitary kidney. Study groups included (1) children 1 to 2 years, (2) girls older than 2 years and boys 2 to 13 years, and (3) boys older than 13 years. Serum creatinine concentrations and estimated glomerular filtration rate were calculated for each group. The mean serum creatinine concentrations in group 1 was 0.4+/-0.1 mg/dL, group 2 was 0.6+/-0.2 mg/dL, and group 3 was 1.1+/-0.2 mg/dL. An estimated glomerular filtration rate 2 SD below the mean suggests further investigation. An estimated glomerular filtration rate 2 SD below the mean was 78 mL/min/1.73 m(2) in group 1, 73 mL/min/1.73 m(2) in group 2, and 70 mL/min/1.73 m(2) in group 3.

Salt sensitivity of children with low birth weight

Compromised intrauterine fetal growth leading to low birth weight (<2500 g) is associated with adulthood renal and cardiovascular disease. The aim of this study was to assess the effect of salt intake on blood pressure (salt sensitivity) in children with low birth weight. White children (n=50; mean age: 11.3+/-2.1 years) born with low (n=35) or normal (n=15) birth weight and being either small or appropriate for gestational age (n=25 in each group) were investigated. The glomerular filtration rate was calculated using the Schwartz formula, and renal size was measured by ultrasound. Salt sensitivity was assigned if mean 24-hour blood pressure increased by >or=3 mm Hg on a high-salt diet as compared with a controlled-salt diet. Baseline office blood pressure was higher and glomerular filtration rate lower in children born with low birth weight as compared with children born at term with appropriate weight (P<0.05). Salt sensitivity was present in 37% and 47% of all of the low birth weight and small for gestational age children, respectively, higher even than healthy young adults from the same region. Kidney length and volume (both P<0.0001) were reduced in low birth weight children. Salt sensitivity inversely correlated with kidney length (r(2)=0.31; P=0.005) but not with glomerular filtration rate. We conclude that a reduced renal mass in growth-restricted children poses a risk for a lower renal function and for increased salt sensitivity. Whether the changes in renal growth are causative or are the consequence of the same abnormal "fetal programming" awaits clarification.

Validation of child serum creatinine-based prediction equations for glomerular filtration rate

Equations for estimating glomerular filtration rate (GFR) are vital in caring for patients with renal disease and the current standard, the Schwartz formula, lacks precision. We evaluated several child serum creatinine-based GFR prediction equations. Subjects aged 2-21 years who underwent iothalamate GFR (IoGFR) testing between 1999 and 2004 were studied retrospectively. GFR was estimated using: (1) Schwartz formula (SchwartzGFR), using a local k value; (2) Schwartz model (SchwartzMod) using regression-derived coefficients; (3) Leger GFR (LegerGFR) using original coefficients; and (4) Leger model (LegerMod) using regression-derived coefficients. Bias, precision, and diagnostic characteristics were evaluated. There were 195 subjects [61% male; mean (SD) age 12.4 (4.5) years; mean (SD) IoGFR 78.9 (33.4) ml/min per 1.73 m(2)]. Only the LegerGFR overestimated IoGFR (5.5 ml/min per 1.73 m(2)). Precision for all formulae was poor (95% limits of agreement approximately -40 to 40 ml/min per 1.73 m(2)), but >or=72% of estimates were within 30% of IoGFR. Sensitivities for detecting IoGFR <30 and 90 ml/min per 1.73 m(2) were highest using the SchwartzGFR (80%) and SchwartzMod (90%), respectively. The LegerGFR was most specific. Using local coefficients, the Schwartz and Leger models were imprecise estimates of GFR, but the Schwartz model was most unbiased and sensitive. Future research should derive more precise equations for GFR in children.

Essentials of laboratory medicine for the nephrology clinician

The purpose of this review is to compile and bring to the attention of the pediatric nephrology community various aspects of laboratory medicine pertinent to nephrology. The review addresses different aspects in laboratory medicine that should be taken into account during interpretation of a test result, such as methodological and analytical issues, statistical considerations and the biological interpretation of a test result in the context of the clinical setting. An understanding of the considerations and limitations in laboratory medicine will be helpful to the pediatric nephrologist when ordering and interpreting biochemical tests.

Determination of proteins in infant formula by high-performance liquid chromatography–electrospray tandem mass spectrometry

To determine the protein content of formula, gel electrophoresis was performed on the infant formula samples and the entire protein patterns were analyzed by nano-high performance liquid chromatography-electrospray tandem mass spectrometry (nano-HPLC/ESI/MS/MS). From the commercial infant formula profiled in this study, a total of 154 peptides, corresponding to 31 unique proteins were identified by nano-HPLC/ESI/MS/MS. Each of the identified peptides was reconfirmed by a strict integrated approach using tandem mass spectra. This protein profiling method using gel electrophoresis coupled with nano-HPLC/ESI/MS/MS and manual evaluation is a sensitive and accurate method for protein identification as well as a powerful tool for monitoring various types of food products.

Diuretics in pediatrics : current knowledge and future prospects

This review summarizes current knowledge on the pharmacology, pharmacokinetics, pharmacodynamics, and clinical application of the most commonly used diuretics in children. Diuretics are frequently prescribed drugs in children. Their main indication is to reduce fluid overload in acute and chronic disease states such as congestive heart failure and renal failure. As with most drugs used in children, optimal dosing schedules are largely unknown and empirical. This is undesirable as it can potentially result in either under- or over-treatment with the possibility of unwanted effects. The pharmacokinetics of diuretics vary in the different pediatric age groups as well as in different disease states. To exert their action, all diuretics, except spironolactone, have to reach the tubular lumen by glomerular filtration and/or proximal tubular secretion. Therefore, renal maturation and function influence drug delivery and consequently pharmacodynamics. Currently advised doses for diuretics are largely based on adult pharmacokinetic and pharmacodynamic studies. Therefore, additional pharmacokinetic and pharmacodynamic studies for the different pediatric age groups are necessary to develop dosing regimens based on pharmacokinetic and pharmacodynamic models for all routes of administration.

Derivation and Validation of Cystatin C–Based Prediction Equations for GFR in Children

BACKGROUND

Cystatin C (CysC) may be a better marker of glomerular filtration rate (GFR) than serum creatinine (SCr) level. Few studies derived CysC-based GFR prediction equations for children. Objectives of this study are to: (1) derive CysC-based GFR prediction equations for children, and (2) compare these equations with published formulae.

METHODS

Patients younger than 18 years undergoing iothalamate GFR (IoGFR) testing were studied prospectively. Data collected were age, sex, CysC level, SCr level, IoGFR, height, weight, and diagnosis. By using linear regression, 2 equations were derived and compared with 3 previously published formulae by using Bland-Altman analysis and diagnostic characteristics. Local coefficients were derived for comparison formulae.

RESULTS

There were 111 GFR tests from 103 patients (age, 12.7 +/- 4.7 years; IoGFR, 73.6 +/- 35.7 mL/min/1.73 m(2) [1.23 +/- 0.60 mL/s/1.73 m(2)]; 60% male; and 25% post-renal transplantation). The 2 equations derived were the CysEq (including CysC level) and the CysCrEq (including CysC and SCr levels). Overall, the 2 new equations had bias and precision similar to previously published formulae when local coefficients were used. However, in patients with a renal transplant or spina bifida, the 2 new equations were less biased and more precise. All CysC-based equations performed better than the Schwartz formula.

CONCLUSION

This study provides 2 CysC-based GFR prediction equations that are accurate, precise, and sensitive for detecting abnormal GFRs. Three previously published CysC GFR prediction equations have been validated for the first time. Prediction equations based on CysC level are likely to provide more accurate estimates of GFR than SCr-based equations.

Estimating pediatric glomerular filtration rates in the era of chronic kidney disease staging

With the use of information from a database of pediatric patients with concomitant nuclear GFR and serum creatinine (Cr), estimated GFR equations were derived on the basis of local laboratory methods and population. These formulas then were compared with those recommended by the National Kidney Foundation for estimating GFR in children. For this, their ability to estimate accurately an individual's true GFR and chronic kidney disease stage, identify patients whose true GFR was <60 ml/min per 1.73 m(2), and to identify correctly deterioration in an individual's GFR over time was compared. Next, two methods to estimate GFR in children without the use of height or weight were developed. The first was a height- and weight-independent formula; the second was a novel approach using the Schwartz formula and calculating a Cr cutoff based on age-based estimates of height and GFR level of interest, i.e., <60 ml/min per 1.73 m(2). Our results suggest that if local laboratory constants are derived and a height is known, then the Schwartz formula offers the most accuracy with least mathematical complexity to perform in the clinical setting. If height is not available but the local laboratory constants have been derived, then the British Columbia's Children's Hospital 2 formula is of value; however, in the setting of estimating pediatric renal function in the outpatient laboratory, where neither of these factors is commonly known, an approach whereby a Cr cutoff for a GFR of interest is developed is suggested. Provided are Cr levels that are based on a reference method of Cr measurement to facilitate this approach for the clinician.

Estimation of the glomerular filtration rate in children: which algorithm should be used?

Glomerular filtration rate (GFR) in children can be estimated by the formula GFR=k x BH/Pcr (where BH is body height in centimetres and Pcr is the plasma creatinine concentration in micromoles per litre). For k, several values have been reported: k=38 (Counahan), k=40 (Morris) and k=48.7 (Schwartz). In this study the predictive performance of these formulae was compared with that of newly developed formulae. GFR measurements based on inulin concentration time curves were divided into an index (n=58) and a validation data set (n=48). In the index data set a value for k was derived by application of nonlinear mixed-effect modelling. This approach was also used to develop a formula that better explained the relationship between patient factors and GFR. Bias and precision of all formulae were calculated for the validation data set. In the index data set a value of 41.2 was found for k, which was close to the value k=40 (Morris). Both formulae estimated GFR well (bias <5%; precision 25%). Further modelling of the relationship between patient factors and GFR did not improve the predictive performance. In our hospital GFR was best estimated by the formula with k=40 and k=41.2. It is recommended that the optimal value for k be assessed locally.

Long-term outcome of meningococcal sepsis-associated acute renal failure

SETTING

Twenty-one of 209 children admitted to the intensive care unit with meningococcal septicemia developed oliguric acute renal failure necessitating renal replacement therapy.

PATIENTS

Twelve survivors underwent renal assessment at a median of 4.2 yrs postpresentation.

RESULT

Two had abnormal glomerular filtration rate, proteinuria, and hypertension; one had isolated proteinuria; and one had an isolated renal parenchymal defect on DMSA scan.

CONCLUSION

Long-term follow-up of this population is recommended.