Estimating Pediatric Glomerular Filtration Rates in the Era of Chronic Kidney Disease Staging

Abstract

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 weightindependent 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. . The National Kidney Foundation (NKF) has recognized that to "further improve dialysis outcomes, it is necessary to improve the health status of those who reach ESRD . . . from earliest kidney damage through the various stages of progression to kidney failure" (3). As a first step toward achieving this goal, the NKF developed a chronic kidney disease (CKD) classification system, the NKF Disease Outcomes Quality Initiative (NKF-DOQI) classification, to "improve/standardize" care of the patient at all stages of CKD (3).In the adult nephrology literature, a move toward classification and management of CKD on the basis of GFR has led to the proposal for widespread implementation of equations to calculated estimated GFR (eGFR) (4). These equations are often derived from studies in patients with particular illnesses, e.g., cancer (5,6), renal dysfunction (7,8), and organ transplantation (9 -11). They use some combination of easily obtained demographics (e.g., height, weight, gender, race) and serum measurements (e.g., creatinine [Cr], urea, albumin) (12) to calculate the individual's GFR or Cr clearance.Similarly, the pediatric members of the NKF CKD working group clearly stated that "major emphasis is placed on the identification of children and adolescents with CKD by measuring the protein-to-Cr ratio in spot urine specimens and by estimating the GFR from serum Cr using prediction equations" (13).Recog...

New Equations to Estimate GFR in Children with CKD

“…With regard to other studies recently published using enzymatic creatinine method to estimate GFR via k[height/ Scr] and measuring true GFR with a reliable method, k values in children and girls older than 13 were 0.500, 28 0.430, 29 0.470, 30 and 0.460, 31 compared with the 0.413 determined in this study. Note also that each of these other studies included individuals with normal and near-normal renal function, whereas children in CKiD were selected on the basis of reduced GFR with the mean and median approximating 40 ml/min per 1.73 m 2 .…”

A simple height-independent equation for estimating glomerular filtration rate in children

“…We previously [3] demonstrated the superiority of the updated Schwartz and FM equations over other heightdependent (BCCH1 [19]) and height-independent eGFR equations for children (Lund-Malmö [20]). Still two other height-independent equations, the BCCH2 [19] and the modified BCCH [1] disserve our attention. The performance (expressed in terms of the parameters listed in Table 1) of all these equations was worse than the performance of the simple height-independent equation (results not shown).…”

Adolescent Type 1 Diabetes Cardio-Renal Intervention Trial (AdDIT): Urinary Screening and Baseline Biochemical and Cardiovascular Assessments

“…Estimated glomerular filtration rate (eGFR) was calculated from plasma creatinine with the following formula: eGFR (mL/min/1.73 m 2 ) = 42 * height (cm) / plasma creatinine (mmol/L) (20).…”