A Pilot Comparative Study between Creatinine- and Cystatin-C-Based Equations to Estimate GFR and Kidney Ultrasound Percentiles in Children with Congenital Anomalies of the Kidney and Urinary Tract

Abstract

Congenital anomalies affecting the kidneys present significant challenges in pediatric nephrology, needing precise methods for assessing renal function and guiding therapeutic intervention. Bedside Schwartz formula with the cystatin-C-based Full Age Spectrum formula and Chronic Kidney Disease in Children (CKiD) U 25 formula used in estimating glomerular filtration rate (eGFR) and also to assess if the eGFR in association with kidney length percentiles can be a monitoring parameter for the progression of chronic kidney disease in children with congenital anomalies of the kidney and urinary tract (CAKUT). A total of 64 pediatric patients (median age at diagnostic was 12 months with an interquartile range of 2 to 60) were diagnosed with congenital anomalies in the kidney and urinary tract between June 2018 and May 2023 at "Louis Turcanu" Emergency Hospital for Children in Timisoara, Romania. Baseline characteristics, CAKUT types, associated pathologies, CKD staging, and eGFR using creatinine and cystatin C were analyzed. The mean age at the moment of examination was 116.50 months; (65, 180). Chronic kidney disease staging revealed a predominance of patients in CKD stages G1 and A1. Analysis of eGFR methods revealed a small mean difference between eGFR estimated by creatinine and cystatin C, with a moderate-strong positive correlation observed between the eGFR and ultrasound parameters. Using cystatin-C-based formulas for eGFR, in conjunction with ultrasound measurements, may offer reliable insights into renal function in pediatric patients with congenital anomalies affecting the kidney and urinary tract. However, the economic aspect must be taken into consideration because cystatin C determination is approximately eight times more expensive than that of creatinine. An interdisciplinary approach is crucial for managing patients with CAKUT.

Keywords: CKid U25; bedside Schwartz equation; congenital anomalies; cystatin C based full age spectrum formula; glomerular filtration rate (eGFR); kidney function assessment; kidney imaging; kidney ultrasound percentiles; pediatric nephrology; urinary tract abnormalities.

Figure 1

Flow diagram of the progress through the stages (enrollment, exclusion criteria, and analysis of the children).

Figure 2

Bland–Altman plot with the following parameters: line of equality (red dotted line), 95% CI of mean difference (green interval), 95% CI of limits of the upper and lower limit of agreement (blue intervals), and regression line of differences (purple dotted line) with 95% CI (orange lines). The orange circles represent plot data from the mean eGFR cystatin and eGFR creatinine (X-axis) and the difference between them (Y-axis) from the same patient. GFR_Cystatin C = eGFR determined using FAS Cystatin C Equation. GFR_ creatinine = eGFR determined using bedside Schwartz formula.

Figure 3

Dot-and-line diagram illustrating the relationship between variables (eGFR creatinine, eGFR cystatin C, eGFR CKID U25): box-and-whisker plot with notches for pairwise comparison, scatter plot showing all data points with a connecting line between them. Each patient is represented by distinct symbols and colors that indicate the estimated values for GFR using various approaches. The connecting lines between them serve to distinguish the variations in the methods employed.

Figure 4

Very strong positive linear association between eGFR creatinine and eGFR cystatin C—scatter diagram and regression line with heat map, 95% confidence interval curve (blue area), 95% prediction interval curve (orange area). The background color of the heat map indicates density of points, suggesting clusters of observations. The red color indicates a high concentration of points, yellow shows a moderate concentration of points, and blue indicates a low concentration of points. The orange circles represent the correspondence between plot data from the eGFR creatinine (X-axis) and eGFR cystatin (Y-axis) from the same patient.

Figure 5

Moderate positive linear association between eGFR cystatin C and percentiles of the left kidney of patients with renal abnormalities—scatter diagram and regression line with heat map, 95% confidence interval curve (blue area), 95% prediction interval curve (orange area). The background color of the heat map shows density of points, suggesting clusters of observations. The red color shows a high concentration of points, yellow indicates a moderate concentration of points, and blue indicates a low concentration of points. The orange circles represent the correspondence between plot data from the eGFR creatinine (X-axis) and percentiles of the left kidney of patients with renal abnormalities (Y-axis) from the same patient.

Figure 6

Proposed algorithm for diagnosis and follow-up in patients suspected of CAKUT for practitioners.