Evaluation of the creatinine-based chronic kidney disease in children (under 25 years) equation in healthy children and adolescents

BACKGROUND

The Chronic Kidney Disease in children (CKiD) equation to estimate glomerular filtration rate eGFR = k × Ht / SCr (Ht = height in cm, SCr = serum creatinine in mg/dL), with fixed k = 0.413, has recently been optimized by introducing age/sex dependent k-values valid for young children up to young adults (the CKiD Under 25 years (CKiDU25) equation). Although the CKiD equation was designed for children with chronic kidney disease (CKD), this equation found common use both clinically and in research, and also in children without CKD. This report aims to evaluate properties of CKiD and CKiDU25 in healthy children and adolescents.

METHOD

Sex-specific metadata (height and creatinine) for healthy children were obtained from national growth curves and creatinine versus age curves. These data were used to calculate average CKiD and CKiDU25 values for each year of age and compare them against age-independent measured GFR of 107 mL/min/1.73 m².

RESULTS

The CKiD estimations show a steep decline with age (1.5 mL/min/1.73 m²/year in females and 2.0 mL/min/1.73 m²/year in males) over the entire age range (2-20 years) and large differences between adolescent males and females. Due to the age/sex specific k-values, the CKiDU25 equation solves this age-decline artifact of the CKiD equation. However, CKiDU25 still shows a systematic higher estimation of about 10% in healthy males compared to females over the entire age range.

CONCLUSION

Although the CKiDU25 shows major improvements compared to the CKiD equation, as the unexpected age decline has been removed, a systematic difference is still observed between healthy males and females.

Cardiovascular Disease Risk Factors in Chronic Kidney Disease in Children

Over the past 2 decades, cardiovascular (CV) disease has been recognized as one of the most important complications of chronic kidney disease (CKD) and one of the leading causes of death in children with advanced CKD and in young adults who developed CKD during childhood. CV abnormalities develop early and progress during the course of CKD in children. Characterization of the prevalence and evolution of CV disease risk factors in progressive CKD is one of the primary aims of the Chronic Kidney Disease in Children study. In this review, we summarize up-to-date findings from the Chronic Kidney Disease in Children study with a focus on traditional and CKD-related CV risk factors and early subclinical markers of cardiac and vascular structure and function. We also discuss the effect of CV risk factors on progression of CKD.

Association of GSTM1 Deletion With Progression of CKD in Children: Findings From the Chronic Kidney Disease in Children (CKiD) Study

RATIONALE AND OBJECTIVE

Loss of function of the product of the GSTM1 gene has been implicated in rapid progression of adult CKD. Its role in pediatric CKD has not been previously described.

STUDY DESIGN

The study is a secondary analysis of a prospective observational cohort examining the association between deletions in GSTM1 and progression of CKD.

SETTING AND PARTICIPANTS

We used data and samples from the prospective Chronic Kidney Disease in Children (CKiD) cohort aged 1-16 years at enrollment with CKD.

EXPOSURE

We defined exposure fewer than two GSTM1 alleles on real-time polymerase chain reaction amplification.

OUTCOME

The primary outcome was a composite of 50% decrease in estimated glomerular filtration rate (eGFR) or start of kidney replacement therapy. Secondary outcomes included remission of proteinuria in children with glomerular disease and cardiovascular complications.

ANALYTIC APPROACH

The primary analysis was by Cox proportional hazards model. Analysis was adjusted for age, sex, race, ethnicity, BMI category, diagnosis category, and eGFR.

RESULTS

674 children were included in the analysis. Mean age at most recent visit was 11.9 years; 61% were male and 20% were Black. There were 241 occurrences of the primary outcome at the time of analysis. After adjustment for baseline characteristics, the risk of progression of CKD for exposed children was 1.94 (1.27, 2.97). The effect size was similar with either one or two deletions (autosomal dominant inheritance). The relationships between number of functional GSTM1 alleles and prespecified secondary outcomes were not statistically significant after adjustment.

LIMITATIONS

Missing data, especially for secondary outcomes, and relatively small sample size compared to genetic studies in adults.

CONCLUSIONS

GSTM1 deletion is associated with more rapid progression of pediatric CKD after adjustment in this large prospective cohort. No statistically significant associations were seen with secondary outcomes. If replicated, these findings may inform development of interventions for CKD in children.

Prediction of kidney failure in children with chronic kidney disease and obstructive uropathy

BACKGROUND

Obstructive uropathy (OU) is a leading cause of pediatric kidney injury. Accurate prediction of kidney disease progression may improve clinical outcomes. We aimed to examine discrimination and accuracy of a validated kidney failure risk equation (KFRE), previously developed in adults, in children with OU.

METHODS

We identified 118 children with OU and an estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 in the Chronic Kidney Disease in Children study, a national, longitudinal, observational cohort. Each patient's 5-year risk of kidney failure was estimated using baseline data and published parameters for the 4- and 8-variable KFREs. Discriminative ability of the KFRE was estimated using the C statistic for time-to-event analysis. Sensitivity and specificity were evaluated across varying risk thresholds.

RESULTS

Among the 118 children, 100 (85%) were boys, with median baseline age of 10 years (interquartile range, 6-14). Median eGFR was 42 mL/min/1.73m 2 (32-53), with a median follow-up duration of 4.5 years (2.7-7.2); 23 patients (19.5%) developed kidney failure within 5 years. The 4-variable KFRE discriminated kidney failure risk with a C statistic of 0.75 (95% CI, 0.68-0.82). A 4-variable risk threshold of ≥ 30% yielded 82.6% sensitivity and 75.0% specificity. Results were similar using the 8-variable KFRE.

CONCLUSIONS

In children with OU, the KFRE discriminated the 5-year risk of kidney failure at C statistic values lower than previously published in adults but comparable with suboptimal values reported in the overall CKiD population. The 8-variable equation did not improve model discrimination or accuracy, suggesting the need for continued research into additional, disease-specific markers.

Longitudinal kidney injury biomarker trajectories in children with obstructive uropathy

BACKGROUND

Congenital obstructive uropathy (OU) is a leading cause of pediatric kidney failure, representing a unique mechanism of injury, in part from renal tubular stretch and ischemia. Tubular injury biomarkers have potential to improve OU-specific risk stratification.

METHODS

Patients with OU were identified in the Chronic Kidney Disease in Children (CKiD) study. "Cases" were defined as individuals receiving any kidney replacement therapy (KRT), while "controls" were age- and time-on-study matched and KRT free at last study visit. Urine and plasma neutrophil gelatinase-associated lipocalin (NGAL), interleukin 18 (IL-18), and liver-type fatty acid-binding protein (L-FABP) levels were measured at enrollment and annually and compared between cases and controls. Urine values were normalized to urine creatinine.

RESULTS

In total, 22 cases and 22 controls were identified, with median (interquartile range) ages of 10.5 (9.0-13.0) and 15.9 (13.9-16.9) years at baseline and outcome, respectively. At enrollment there were no differences noted between cases and controls for any urine (u) or plasma (p) biomarker measured. However, the mean pNGAL and uL-FABP/creatinine increased throughout the study period in cases (15.38 ng/ml per year and 0.20 ng/ml per mg/dl per year, respectively, p = 0.01 for both) but remained stable in controls. This remained constant after controlling for baseline glomerular filtration rate (GFR).

CONCLUSIONS

In children with OU, pNGAL and uL-FABP levels increased over the 5 years preceding KRT; independent of baseline GFR. Future studies are necessary to identify optimal cutoff values and to determine if these markers outperform current clinical predictors.

Blood pressure in children with chronic kidney disease: lessons learned from the Chronic Kidney Disease in Children Cohort Study

Cardiovascular disease (CVD) is common among children and adolescents with chronic kidney disease (CKD) and end-stage kidney disease (ESRD). However, the early accrual of CVD risk factors in children with CKD has not been well studied. The Chronic Kidney Disease in Children (CKiD) Study, a multicenter, prospective cohort study of children with mild-to-moderate CKD at study entry counts among its primary aims investigation of the drivers of CVD risk in this population. As the most prevalent CVD risk factor in children with CKD, blood pressure (BP) has been a major focus of investigation for the CKiD Study Group. Over the first 15 years of the study, landmark publications have better defined the prevalence of hypertension, the frequency with which it is under-recognized and thus undertreated, and the consequences of elevated BP in this cohort. The purpose of this review is to summarize the contributions made by the CKiD Study in advancing knowledge of BP in this high-risk population, and to highlight areas in need of further study.

A longitudinal examination of parent-reported emotional-behavioral functioning of children with mild to moderate chronic kidney disease

BACKGROUND

Children with mild to moderate chronic kidney disease (CKD) are at increased risk for deficits in neurocognition. Less is known about how CKD affects emotional-behavioral functioning in this population.

METHODS

Parent ratings of emotional-behavioral functioning at baseline and over time were examined for 845 children with mild to moderate CKD using the Behavior Assessment System for Children, Second Edition Parent Rating Scales (BASC-2 PRS). Associations with demographic and disease-related predictors were also examined.

RESULTS

Children with mild to moderate CKD had parent-reported emotional-behavioral functioning largely within normal limits, at baseline and over time. The proportion with T-scores at least 1 SD above the mean was 24% for Internalizing Problems and 28% for Attention Problems. A greater proportion of participants scored lower than expected (worse) on scales measuring adaptive skills (25%). Persistent hypertension predicted attention problems (β = 1.59, 95% CI = 0.24 to 2.94, p < 0.02) and suggested worse behavioral symptoms (β = 1.36, 95% CI = - 0.01 to 2.73, p = 0.05). Participants with proteinuria at baseline, but not at follow-up, had fewer attention problems than participants whose proteinuria had not resolved (β = - 3.48, CI = - 6.79 to - 0.17, p < 0.04). Glomerular diagnosis was related to fewer (β = - 2.68, 95% CI = - 4.93 to - 0.42, p < 0.02) internalizing problems.

CONCLUSIONS

Although children with CKD generally have average emotional-behavioral parent ratings, a notable percentage of the population may be at risk for problems with attention and adaptive behavior. Providers working with this population should facilitate psychosocial referrals when indicated.

Common clinical markers predict end-stage renal disease in children with obstructive uropathy

BACKGROUND

Obstructive uropathy (OU) is a common cause of end-stage renal disease (ESRD) in children. Children who escape the newborn period with mild-to-moderate chronic kidney disease (CKD) continue to be at increased risk. The predictive ability of clinically available markers throughout childhood is poorly defined.

METHODS

Patients with OU were identified in the Chronic Kidney Disease in Children Study. The primary outcome of interest was renal replacement therapy (RRT) (cases). Controls were age matched and defined as patients within the OU cohort who did not require RRT during study follow-up.

RESULTS

In total, 27 cases and 41 age-matched controls were identified. Median age at baseline and age at outcome measurement were 10 vs. 16 years, respectively. First available glomerular filtration rate (GFR) (36.9 vs. 53.5 mL/min per 1.73 m²), urine protein/creatinine (Cr) (0.40 vs. 0.22 mg/mg) and microalbumin/Cr (0.58 vs. 0.03 mg/mg), and serum CO₂ (20 vs. 22 mmol/L) and hemoglobin (12.4 vs. 13.2 g/dL) differed significantly between cases and controls, respectively. GFR declined 3.07 mL/min per 1.73 m²/year faster in cases compared to that in controls (p < 0.0001). Urine protein/Cr and microalbumin/Cr increased by 0.16 and 0.11 per year more in cases compared to those in controls, respectively (p ≤ 0.001 for both). Serum phosphate increased by 0.11 mg/dL and serum albumin and hemoglobin decreased by 0.04 (g/dL) and 0.14 (g/dL) per year more for cases compared to those for controls, respectively (p < 0.05 for all).

CONCLUSIONS

Age-specific baseline and longitudinal measures of readily available clinical measures predict progression to ESRD in children with mild-to-moderate CKD from OU.

Fibroblast Growth Factor 23 and Risk of CKD Progression in Children

BACKGROUND AND OBJECTIVES

Plasma fibroblast growth factor 23 (FGF23) concentrations increase early in the course of CKD in children. High FGF23 levels associate with progression of CKD in adults. Whether FGF23 predicts CKD progression in children is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We tested the hypothesis that high plasma FGF23 is an independent risk factor for CKD progression in 419 children, aged 1-16 years, enrolled in the Chronic Kidney Disease in Children (CKiD) cohort study. We measured plasma FGF23 concentrations at baseline and determined GFR annually using plasma disappearance of iohexol or the CKiD study estimating equation. We analyzed the association of baseline FGF23 with risk of progression to the composite end point, defined as start of dialysis or kidney transplantation or 50% decline from baseline GFR, adjusted for demographics, baseline GFR, proteinuria, other CKD-specific factors, and other mineral metabolites.

RESULTS

At enrollment, median age was 11 years [interquartile range (IQR), 8-15], GFR was 44 ml/min per 1.73 m2 (IQR, 33-57), and FGF23 was 132 RU/ml (IQR, 88-200). During a median follow-up of 5.5 years (IQR, 3.5-6.6), 32.5% of children reached the progression end point. Higher FGF23 concentrations were independently associated with higher risk of the composite outcome (fully adjusted hazard ratio, 2.52 in the highest versus lowest FGF23 tertile; 95% confidence interval, 1.44 to 4.39, P=0.002; fully adjusted hazard ratio, 1.33 per doubling of FGF23; 95% confidence interval, 1.13 to 1.56, P=0.001). The time to progression was 40% shorter for participants in the highest compared with the lowest FGF23 tertile. In contrast, serum phosphorus, vitamin D metabolites, and parathyroid hormone did not consistently associate with progression in adjusted analyses.

CONCLUSIONS

High plasma FGF23 is an independent risk factor for CKD progression in children.

The impact of short stature on health-related quality of life in children with chronic kidney disease

OBJECTIVES

To compare the health-related quality of life (HRQoL) of children with chronic kidney disease (CKD) and short stature (SS) with that of children with CKD and normal height (NH), to evaluate the impact of catch-up growth and growth hormone (GH) use on HRQoL, and to describe the concordance of perceptions of HRQoL between children with SS and NH and their parents.

STUDY DESIGN

Four hundred eighty-three children and/or parents enrolled in the multicenter Chronic Kidney Disease in Children study who had completed the Pediatric Quality of Life Inventory (Version 4.0) on at least 2 Chronic Kidney Disease in Children study visits composed this substudy population. Participants were dichotomized into NH or SS groups. The demographic characteristics that varied at baseline (sex, glomerular filtration rate, and parent education) were controlled for in the main analysis evaluating the impact of catch-up growth and use of GH on HRQoL.

RESULTS

Multivariate modeling (controlling for confounding variables) revealed a significant association between both catch-up growth and GH use on parent-proxy reports of child physical functioning (P < .05) and social functioning (P < .05). Older children with CKD (15-17 years old) had significantly higher ratings than their parents on the Pediatric Quality of Life Inventory Physical, Emotional, Social, and School Functioning scales compared with younger children (8-14 years old).

CONCLUSION

The finding that height gains and GH use are associated with increases in physical and social functioning by parent report provides additional support for interventions to improve height in children with CKD. The importance of evaluating both the parent and child perceptions of HRQoL is supported by our results.