Evaluation of novel candidate filtration markers from a global metabolomic discovery for glomerular filtration rate estimation.

Creatinine and cystatin-C are recommended for estimating glomerular filtration rate (eGFR) but accuracy is suboptimal. Here, using untargeted metabolomics data, we sought to identify candidate filtration markers for a new targeted assay using a novel approach based on their maximal joint association with measured GFR (mGFR) and with flexibility to consider their biological properties. We analyzed metabolites measured in seven diverse studies encompasing 2,851 participants on the Metabolon H4 platform that had Pearson correlations with log mGFR and used a stepwise approach to develop models to < -0.5 estimate mGFR with and without inclusion of creatinine that enabled selection of candidate markers. In total, 456 identified metabolites were present in all studies, and 36 had correlations with mGFR < -0.5. A total of 2,225 models were developed that included these metabolites; all with lower root mean square errors and smaller coefficients for demographic variables compared to estimates using untargeted creatinine. Seventeen metabolites were chosen, including 12 new candidate filtration markers. The selected metabolites had strong associations with mGFR and little dependence on demographic factors. Candidate metabolites were identified with maximal joint association with mGFR and minimal dependence on demographic variables across many varied clinical settings. These metabolites are excreted in urine and represent diverse metabolic pathways and tubular handling. Thus, our data can be used to select metabolites for a multi-analyte eGFR determination assay using mass spectrometry that potentially offers better accuracy and is less prone to non-GFR determinants than the current eGFR biomarkers.

Antihypertensive medication nonadherence and target organ damage in children with chronic kidney disease.

BACKGROUND: Nonadherence is common in children with chronic kidney disease (CKD). This may contribute to inadequate blood pressure control and adverse outcomes. This study examined associations between antihypertensive medication nonadherence, ambulatory blood pressure monitoring (ABPM) parameters, kidney function, and cardiac structure among children with CKD. METHODS: We performed secondary analyses of data from the CKD in Children (CKiD) study, including participants with treated hypertension who underwent ABPM, laboratory testing, and echocardiography biannually. Nonadherence was defined by self-report of any missed antihypertensive medication 7 days prior to the study visit. Linear regression and mixed-effects models were used to assess the association of nonadherence with baseline and time-updated ABPM profiles, estimated glomerular filtration rate (eGFR), urine protein to creatinine ratio (UPCR), and left ventricular mass index (LVMI). RESULTS: Five-hundred and eight participants met inclusion criteria, followed for a median of 2.9 years; 212 (42%) were female, with median age 13 years (IQR 10-16), median baseline eGFR 49 (33-64) ml/min/1.73 m2 and median UPCR 0.4 (0.1-1.0) g/g. Nonadherence occurred in 71 (14%) participants. Baseline nonadherence was not significantly associated with baseline 24-h ABPM parameters (for example, mean 24-h SBP [ß - 0.1, 95% CI - 2.7, 2.5]), eGFR (ß 1.0, 95% CI - 0.9, 1.2), UCPR (ß 1.1, 95% CI - 0.8, 1.5), or LVMI (ß 0.6, 95% CI - 1.6, 2.9). Similarly, there were no associations between baseline nonadherence and time-updated outcome measures. CONCLUSIONS: Self-reported antihypertensive medication nonadherence occurred in 1 in 7 children with CKD. We found no associations between nonadherence and kidney function or cardiac structure over time. A higher resolution version of the Graphical abstract is available as Supplementary information.

Pubertal luteinizing hormone levels in children with chronic kidney disease and association with change in glomerular filtration rate.

BACKGROUND: Children with chronic kidney disease (CKD) are at risk for abnormalities in pubertal development. We aimed to describe the timing of pubertal onset by luteinizing hormone (LH) levels and the association between hormonal onset of puberty with changes in GFR. METHODS: Data from the Chronic Kidney Disease in Children (CKiD) study were collected prospectively. GFR was estimated at annual visits and measured by iohexol clearance every other year. LH was measured from stored repository serum samples in a nested sample of 124 participants. Hormonal onset of puberty was defined as LH level greater than or equal to 0.3 IU/L. A mixed effects model with random intercepts and slopes was used to compare the slope of decline of GFR before and after hormonal onset of puberty. The model was adjusted for age, glomerular disease diagnosis, baseline proteinuria on the log scale, and BMI. RESULTS: Median age at hormonal onset of puberty was 9.9 years (IQR 8.1, 11.9) in girls and 10.2 years (IQR 9.2, 11.0) in boys. The mixed effects model showed faster decline in both estimated GFR and measured GFR in boys after hormonal onset of puberty (p < 0.001), and a similar but attenuated accelerated estimated GFR decline was observed for girls with no difference for measured GFR. CONCLUSIONS: LH levels in the post-pubertal range were observed prior to clinical manifestations of puberty in children with CKD. Hormonal onset of puberty was associated with faster decline in GFR, particularly among boys with CKD.

Associations between anemia and FGF23 in the CKiD study.

BACKGROUND: Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that plays a central role in chronic kidney disease-mineral bone disorder and is associated with CKD progression and cardiovascular morbidity. Factors related to CKD-associated anemia, including iron deficiency, can increase FGF23 production. This study aimed to assess whether anemia and/or iron deficiency are associated with increased circulating concentrations of FGF23 in the large, well-characterized Chronic Kidney Disease in Children (CKiD) study cohort. METHODS: Hemoglobin concentrations, iron parameters, C-terminal (total) FGF23, intact FGF23, and relevant covariables were measured in cross-sectional analysis of CKiD study subjects. RESULTS: In 493 pediatric patients with CKD (median [interquartile range] age 13 [9, 16] years), the median estimated glomerular filtration rate was 48 [35, 61] ml/min/1.73 m2, and 103 patients (21%) were anemic. Anemic subjects had higher total FGF23 concentrations than non-anemic subjects (204 [124, 390] vs. 109 [77, 168] RU/ml, p < 0.001). In multivariable linear regression modeling, anemia was independently associated with higher total FGF23, after adjustment for demographic, kidney-related, mineral metabolism, and inflammatory covariables (standardized ß (95% confidence interval) 0.10 (0.04, 0.17), p = 0.002). In the subset of subjects with available iron parameters (n = 191), iron deficiency was not associated with significantly higher total FGF23 concentrations. In the subgroup that had measurements of both total and intact FGF23 (n = 185), in fully adjusted models, anemia was significantly associated with higher total FGF23 (standardized ß (95% CI) 0.16 (0.04, 0.27), p = 0.008) but not intact FGF23 (standardized ß (95% CI) 0.02 (-0.12, 0.15), p = 0.81). CONCLUSIONS: In this cohort of pediatric patients with CKD, anemia was associated with increased total FGF23 levels but was not independently associated with elevated intact FGF23, suggesting possible effects on both FGF23 production and cleavage. Further studies are warranted to investigate non-mineral factors affecting FGF23 production and metabolism in CKD.

Plasma Metabolomics of Dietary Intake of Protein-Rich Foods and Kidney Disease Progression in Children.

OBJECTIVE: Evidence regarding the efficacy of a low-protein diet for patients with CKD is inconsistent and recommending a low-protein diet for pediatric patients is controversial. There is also a lack of objective biomarkers of dietary intake. The purpose of this study was to identify plasma metabolites associated with dietary intake of protein and to assess whether protein-related metabolites are associated with CKD progression. METHODS: Nontargeted metabolomics was conducted in plasma samples from 484 Chronic Kidney Disease in Children (CKiD) participants. Multivariable linear regression estimated the cross-sectional association between 949 known, nondrug metabolites and dietary intake of total protein, animal protein, plant protein, chicken, dairy, nuts and beans, red and processed meat, fish, and eggs, adjusting for demographic, clinical, and dietary covariates. Cox proportional hazards models assessed the prospective association between protein-related metabolites and CKD progression defined as the initiation of kidney replacement therapy or 50% eGFR reduction, adjusting for demographic and clinical covariates. RESULTS: One hundred and twenty-seven (26%) children experienced CKD progression during 5 years of follow-up. Sixty metabolites were significantly associated with dietary protein intake. Among the 60 metabolites, 10 metabolites were significantly associated with CKD progression (animal protein: n = 1, dairy: n = 7, red and processed meat: n = 2, nuts and beans: n = 1), including one amino acid, one cofactor and vitamin, 4 lipids, 2 nucleotides, one peptide, and one xenobiotic. 1-(1-enyl-palmitoyl)-2-oleoyl-glycerophosphoethanolamine (GPE, P-16:0/18:1) was positively associated with dietary intake of red and processed meat, and a doubling of its abundance was associated with 88% higher risk of CKD progression. 3-ureidopropionate was inversely associated with dietary intake of red and processed meat, and a doubling of its abundance was associated with 48% lower risk of CKD progression. CONCLUSIONS: Untargeted plasma metabolomic profiling revealed metabolites associated with dietary intake of protein and CKD progression in a pediatric population.

Genomic Disorders in CKD across the Lifespan.

SIGNIFICANCE STATEMENT: Pathogenic structural genetic variants, also known as genomic disorders, have been associated with pediatric CKD. This study extends those results across the lifespan, with genomic disorders enriched in both pediatric and adult patients compared with controls. In the Chronic Renal Insufficiency Cohort study, genomic disorders were also associated with lower serum Mg, lower educational performance, and a higher risk of death. A phenome-wide association study confirmed the link between kidney disease and genomic disorders in an unbiased way. Systematic detection of genomic disorders can provide a molecular diagnosis and refine prediction of risk and prognosis. BACKGROUND: Genomic disorders (GDs) are associated with many comorbid outcomes, including CKD. Identification of GDs has diagnostic utility. METHODS: We examined the prevalence of GDs among participants in the Chronic Kidney Disease in Children (CKiD) cohort II ( n =248), Chronic Renal Insufficiency Cohort (CRIC) study ( n =3375), Columbia University CKD Biobank (CU-CKD; n =1986), and the Family Investigation of Nephropathy and Diabetes (FIND; n =1318) compared with 30,746 controls. We also performed a phenome-wide association analysis (PheWAS) of GDs in the electronic MEdical Records and GEnomics (eMERGE; n =11,146) cohort. RESULTS: We found nine out of 248 (3.6%) CKiD II participants carried a GD, replicating prior findings in pediatric CKD. We also identified GDs in 72 out of 6679 (1.1%) adult patients with CKD in the CRIC, CU-CKD, and FIND cohorts, compared with 199 out of 30,746 (0.65%) GDs in controls (OR, 1.7; 95% CI, 1.3 to 2.2). Among adults with CKD, we found recurrent GDs at the 1q21.1, 16p11.2, 17q12, and 22q11.2 loci. The 17q12 GD (diagnostic of renal cyst and diabetes syndrome) was most frequent, present in 1:252 patients with CKD and diabetes. In the PheWAS, dialysis and neuropsychiatric phenotypes were the top associations with GDs. In CRIC participants, GDs were associated with lower serum magnesium, lower educational achievement, and higher mortality risk. CONCLUSION: Undiagnosed GDs are detected both in children and adults with CKD. Identification of GDs in these patients can enable a precise genetic diagnosis, inform prognosis, and help stratify risk in clinical studies. GDs could also provide a molecular explanation for nephropathy and comorbidities, such as poorer neurocognition for a subset of patients.

Development of an adaptive clinical web-based prediction tool for kidney replacement therapy in children with chronic kidney disease.

Clinicians need improved prediction models to estimate time to kidney replacement therapy (KRT) for children with chronic kidney disease (CKD). Here, we aimed to develop and validate a prediction tool based on common clinical variables for time to KRT in children using statistical learning methods and design a corresponding online calculator for clinical use. Among 890 children with CKD in the Chronic Kidney Disease in Children (CKiD) study, 172 variables related to sociodemographics, kidney/cardiovascular health, and therapy use, including longitudinal changes over one year were evaluated as candidate predictors in a random survival forest for time to KRT. An elementary model was specified with diagnosis, estimated glomerular filtration rate and proteinuria as predictors and then random survival forest identified nine additional candidate predictors for further evaluation. Best subset selection using these nine additional candidate predictors yielded an enriched model additionally based on blood pressure, change in estimated glomerular filtration rate over one year, anemia, albumin, chloride and bicarbonate. Four additional partially enriched models were constructed for clinical situations with incomplete data. Models performed well in cross-validation, and the elementary model was then externally validated using data from a European pediatric CKD cohort. A corresponding user-friendly online tool was developed for clinicians. Thus, our clinical prediction tool for time to KRT in children was developed in a large, representative pediatric CKD cohort with an exhaustive evaluation of potential predictors and supervised statistical learning methods. While our models performed well internally and externally, further external validation of enriched models is needed.

Longitudinal Relationship Between Anemia and Statural Growth Impairment in Children and Adolescents With Nonglomerular CKD: Findings From the Chronic Kidney Disease in Children (CKiD) Study.

RATIONALE & OBJECTIVE: Anemia and statural growth impairment are both prevalent in children with nonglomerular chronic kidney disease (CKD) and are associated with poor quality of life and increased morbidity and mortality. However, to date no longitudinal studies have demonstrated a relationship between anemia and statural growth in this population. STUDY DESIGN: The CKD in Children (CKiD) study is a multicenter prospective cohort study with over 15 years of follow-up observation. SETTING & PARTICIPANTS: CKiD participants younger than 22 years with nonglomerular CKD who had not reached final adult height. EXPOSURE: Age-, sex-, and race-specific hemoglobin z score. OUTCOME: Age- and sex-specific height z score. ANALYTICAL APPROACH: The relationship between hemoglobin and height was quantified using (1) multivariable repeated measures paired person-visit analysis, and (2) multivariable repeated measures linear mixed model analysis. Both models were adjusted for age, sex, body mass index, estimated glomerular filtration rate, acidosis, and medication use. RESULTS: Overall, 67% of the 510 participants studied had declining hemoglobin z score trajectories over the follow-up period, which included 1,763 person-visits. Compared with average hemoglobin z scores of≥0, average hemoglobin z scores of less than -1.0 were independently associated with significant growth impairment at the subsequent study visit, with height z score decline ranging from 0.24 to 0.35. Importantly, in 50% of cases hemoglobin z scores of less than -1.0 corresponded to hemoglobin values higher than those used as cutoffs defining anemia in the KDIGO clinical practice guideline for anemia in CKD. When stratified by age, the magnitude of the association peaked in participants aged 9 years. In line with paired-visit analyses, our mixed model analysis demonstrated that in participants with baseline hemoglobin z score less than -1.0, a hemoglobin z score decline over the follow-up period was associated with a statistically significant concurrent decrease in height z score. LIMITATIONS: Limited ability to infer causality. CONCLUSIONS: Hemoglobin decline is associated with growth impairment over time in children with mild to moderate nonglomerular CKD, even before hemoglobin levels reach the cutoffs that are currently used to define anemia in this population.

Blood Pressure Classification Status in Children With CKD Following Adoption of the 2017 American Academy of Pediatrics Guideline.

RATIONALE & OBJECTIVE: Accurate detection of hypertension is crucial for clinical management of pediatric chronic kidney disease (CKD). The 2017 American Academy of Pediatrics (AAP) clinical practice guideline for childhood hypertension included new normative blood pressure (BP) values and revised definitions of BP categories. In this study, we examined the effect of applying the AAP guideline's normative data and definitions to the Chronic Kidney Disease in Children (CKiD) cohort compared with use of normative data and definitions from the 2004 Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents. STUDY DESIGN: Observational cohort study. SETTING & PARTICIPANTS: Children and adolescents in the CKiD cohort. EXPOSURE: Clinic BP measurements. OUTCOME: BP percentiles and hypertension stages calculated using the 2017 AAP guideline and the Fourth Report from 2004. ANALYTICAL APPROACH: Agreement analysis compared the estimated percentile and prevalence of high BP based on the 2017 guideline and 2004 report to clinic and combined ambulatory BP readings. RESULTS: The proportion of children classified as having normal clinic BP was similar using the 2017 and 2004 systems, but the use of the 2017 normative data classified more participants as having stages 1-2 hypertension (22% vs 11%), with marginal reproducibility (κ=0.569 [95% CI, 0.538-0.599]). Those identified as having stage 2 hypertension by the 2017 guideline had higher levels of proteinuria compared with those identified using the 2004 report. Comparing use of the 2017 guideline and the 2004 report in terms of ambulatory BP monitoring categories, there were substantially more participants with white coat (3.5% vs 1.5%) and ambulatory (15.5% vs 7.9%) hypertension, but the proportion with masked hypertension was lower (40.2% vs 47.8%, respectively), and the percentage of participants who were normotensive was similar (40.9% vs 42.9%, respectively). Overall, there was good reproducibility (κ=0.799 [95% CI, 0.778-0.819]) of classification by ambulatory BP monitoring. LIMITATIONS: Relationship with long-term progression and target organ damage was not assessed. CONCLUSIONS: A greater percentage of children with CKD were identified as having hypertension based on both clinic and ambulatory BP when using the 2017 AAP guideline versus the Fourth Report from 2004, and the 2017 guideline better discriminated those with higher levels of proteinuria. The substantial differences in the classification of hypertension when using the 2017 guideline should inform clinical care.

Identification of Novel Genetic Risk Factors for Focal Segmental Glomerulosclerosis in Children: Results From the Chronic Kidney Disease in Children (CKiD) Cohort.

RATIONALE & OBJECTIVE: Focal segmental glomerulosclerosis (FSGS) is a major cause of pediatric nephrotic syndrome, and African Americans exhibit an increased risk for developing FSGS compared with other populations. Predisposing genetic factors have previously been described in adults. Here we performed genomic screening of primary FSGS in a pediatric African American population. STUDY DESIGN: Prospective cohort with case-control genetic association study design. SETTING & PARTICIPANTS: 140 African American children with chronic kidney disease from the Chronic Kidney Disease in Children (CKiD) cohort, including 32 cases with FSGS. PREDICTORS: Over 680,000 common single-nucleotide polymorphisms (SNPs) were tested for association. We also ran a pathway enrichment analysis and a human leucocyte antigen (HLA)-focused association study. OUTCOME: Primary biopsy-proven pediatric FSGS. ANALYTICAL APPROACH: Multivariate logistic regression models. RESULTS: The genome-wide association study revealed 169 SNPs from 14 independent loci significantly associated with FSGS (false discovery rate [FDR]<5%). We observed notable signals for genetic variants within the APOL1 (P=8.6×10-7; OR, 25.8 [95% CI, 7.1-94.0]), ALMS1 (P=1.3×10-7; 13.0% in FSGS cases vs 0% in controls), and FGFR4 (P=4.3×10-6; OR, 24.8 [95% CI, 6.3-97.7]) genes, all of which had previously been associated with adult FSGS, kidney function, or chronic kidney disease. We also highlighted novel, functionally relevant genes, including GRB2 (which encodes a slit diaphragm protein promoting podocyte structure through actin polymerization) and ITGB1 (which is linked to renal injuries). Our results suggest a major role for immune responses and antigen presentation in pediatric FSGS through (1) associations with SNPs in PTPRJ (or CD148, P=3.5×10-7), which plays a role in T-cell receptor signaling, (2) HLA-DRB1∗11:01 association (P=6.1×10-3; OR, 4.5 [95% CI, 1.5-13.0]), and (3) signaling pathway enrichment (P=1.3×10-6). LIMITATIONS: Sample size and no independent replication cohort with genomic data readily available. CONCLUSIONS: Our genetic study has identified functionally relevant risk factors and the importance of immune regulation for pediatric primary FSGS, which contributes to a better description of its molecular pathophysiological mechanisms. PLAIN-LANGUAGE SUMMARY: We assessed the genetic risk factors for primary focal segmental glomerulosclerosis (FSGS) by simultaneously testing over 680,000 genetic markers spread across the genome in 140 children, including 32 with FSGS lesions. Fourteen independent genetic regions were significantly associated with pediatric FSGS, including APOL1 and ALMS1-NAT8, which were previously found to be associated with FSGS and chronic kidney diseases in adults. Novel genes with relevant biological functions were also highlighted, such as GRB2 and FGFR4, which play a role in the kidney filtration barrier and in kidney cell differentiation, respectively. Finally, we revealed the importance of immune regulation in pediatric FSGS through associations involving cell surface proteins presenting antigens to the immune system and interacting with T-cell receptors.

Improving Clinical Care for Children With CKD: A Report From a National Kidney Foundation Scientific Workshop.

Development of clinical guidelines and recommendations to address the care of pediatric patients with chronic kidney disease (CKD) has rarely included the perspectives of providers from a variety of health care disciplines or the patients and parents themselves. Accordingly, the National Kidney Foundation hosted an in-person, one and a half-day workshop that convened a multidisciplinary group of physicians, allied health care professionals, and pediatric patients with CKD and their parents, with the goal of developing key clinical recommendations regarding best practices for the clinical management of pediatric patients living with CKD. The key clinical recommendations pertained to 5 broad topics: addressing the needs of patients and parents/caregivers; modifying the progression of CKD; clinical management of CKD-mineral and bone disorder and growth retardation; clinical management of anemia, cardiovascular disease, and hypertension; and transition and transfer of pediatric patients to adult nephrology care. This report describes the recommendations generated by the participants who attended the workshop.

Patient-Reported Outcomes Over 24 Months in Pediatric CKD: Findings From the MyKidneyHealth Cohort Study.

RATIONALE & OBJECTIVE: The lived experience of children with chronic kidney disease (CKD) is poorly characterized. We examined the associations between patient-reported outcome (PRO) scores measuring their fatigue, sleep health, psychological distress, family relationships, and global health with clinical outcomes over time in children, adolescents, and younger adults with CKD and investigated how the PRO scores of this group compare with those of other children, adolescents, and younger adults. STUDY DESIGN: Prospective cohort study. SETTING & PARTICIPANTS: 212 children, adolescentss, and adults aged 8 to 21 years with CKD and their parents recruited from 16 nephrology programs across North America. PREDICTORS: CKD stage, disease etiology, and sociodemographic and clinical variables. OUTCOME: PRO scores over 2 years. ANALYTICAL APPROACH: We compared PRO scores in the CKD sample with a nationally representative general pediatric population (ages 8 to 17 years). Change of PROs over time and association of sociodemographic and clinical variables with PROs were assessed using multivariable regression models. RESULTS: For all time points, 84% of the parents and 77% of the children, adolescents, and younger adults completed PRO surveys . The baseline PRO scores for the participants with CKD revealed a higher burden of fatigue, sleep-related impairment, psychological distress, impaired global health, and poorer family relationships compared with the general pediatric population, with median score differences≥1 SD for fatigue and global health. The baseline PRO scores did not differ by CKD stage or glomerular versus nonglomerular etiology. Over 2 years, PROs were stable with a<1-point annual change on average on each measure and intraclass correlation coefficients ranging from 0.53 to 0.79, indicating high stability. Hospitalization and parent-reported sleep problems were associated with worse fatigue, psychological health, and global health scores (all P<0.04). LIMITATIONS: We were unable to assess responsiveness to change with dialysis or transplant. CONCLUSIONS: Children with CKD experience a high yet stable burden of impairment across numerous PRO measures, especially fatigue and global health, independent of disease severity. These findings underscore the importance of assessing PROs, including fatigue and sleep measures, in this vulnerable population. PLAIN-LANGUAGE SUMMARY: Children with chronic kidney disease (CKD) have many treatment demands and experience many systemic effects. How CKD impacts the daily life of a child is poorly understood. We surveyed 212 children, adolescents, and younger adults with CKD and their parents over 24 months to assess the participants' well-being over time. Among children, adolescents, and younger adults with CKD we found a very high and persistent burden of psychological distress that did not differ by degree of CKD or type of kidney disease. The participants with CKD endorsed greater impairment in fatigue and global health compared with healthy children, adolescents, and younger adults, and parent-reported sleep problems were associated with poorer patient-reported outcome (PRO) scores across all domains. These findings emphasize the importance of including PRO measures, including fatigue and sleep measures, into routine clinical care to optimize the lived experience of children with CKD.

Dipping at home: is it better, easier, and more convenient? A feasibility and acceptability study of a novel home urinalysis using a smartphone application.

BACKGROUND: Monitoring proteinuria in patients with kidney disease is of crucial importance given its implications for long-term disease progression and clinical management. Leveraging digital health technology to provide a clinical grade urinalysis result from home holds the potential to greatly enhance the clinical experience and workflows for patients, caregivers, and providers. The goal of this study was to evaluate the acceptability and feasibility of a home-based urinalysis kit using a smartphone application. METHODS: This is a prospective cohort study of children and young adults (5-21 years of age) at a single pediatric center. The study received ethical board approval. Families performed a home urine test using the Healthy.io smartphone app. The app was compared with standard of care of either home dipstick monitoring or urinalysis performed in clinic or a local laboratory. Patient satisfaction was compared between the new app and current practice. RESULTS: A total of 103 children, 63 (61%) male and median age 10.9 years (inter-quartile range 7.8-14.2), were enrolled. Primary diagnosis included 47 (46%) glomerular disease, 48 (47%) non-glomerular kidney disease, and 8 (8%) kidney transplant recipients. One hundred and one (98%) patients reported being satisfied with the smartphone app compared to 41 (40%) patients who were satisfied with the current practice for urine protein monitoring (p < 0.0001). Positive themes identified included ease of use, convenience, and immediacy and accuracy of results. CONCLUSIONS: The Healthy.io home urine testing app received very high rates of satisfaction among patients and caregivers compared to current practice and holds great potential to enhance patient-centered care. A higher resolution version of the Graphical abstract is available as Supplementary information.

Application of GFR estimating equations to children with normal, near-normal, or discordant GFR.

BACKGROUND: The objective was to determine the extent that eGFR formulas correspond to measured plasma iohexol clearance (iGFR) in children with normal or near normal kidney function, particularly how different eGFR formulas yield discordant results. METHODS: iGFR from 2 (iGFR-2pt) and 4 (iGFR-4pt) time points along with creatinine and/or cystatin C-based eGFR were measured in children with mild CKD, stages 1-2. eGFR was calculated using 6 equations: 3 under 25 (U25) formulas from the Chronic Kidney Disease in Children (CKiD) study, the full age-combined cystatin C (cysC) and creatinine spectrum (FAS-combined), the European Kidney Function Consortium (EKFC-creatinine) equation, and the Chronic Kidney Disease Epidemiology Collaboration (CKD-epi) cysC-based equation. RESULTS: Twenty-nine children were included, of which 22 had discordant creatinine vs. cystatin C-based eGFR by ≥ 15mL/min/1.73 m2. Overall, the FAS-combined had the least bias, while the U25 most accurately identified children with an eGFR < 90 mL/min/1.73 m2. When Cr-eGFR was ≥ 15 mL/min higher than CysC-eGFR, the U25 creatinine eGFR was closest to iGFR-4pt. When CysC eGFR was higher, the U25-combined was closest to iGFR-4pt. CONCLUSION: The formulas that most closely approximated the measured GFR varied depending on the pattern of discordant eGFR results. Based on the results, we recommend using the CKiD U25-combined formula to screen for children with a low GFR. Either the CKiD U25-combined or FAS-combined would be recommended for changes in eGFR longitudinally. However, because all formulas were discordant from the iGFR-4pt in over a third of participants, further refinement of pediatric eGFR formulas is needed at the normal/near-normal range. A higher resolution version of the Graphical abstract is available as Supplementary information.

Trajectories of eGFR after kidney transplantation according to trajectories of eGFR prior to kidney replacement therapies in children with chronic kidney disease.

BACKGROUND: In children with chronic kidney disease (CKD), certain risk factors are associated with faster eGFR decline and earlier kidney failure. Whether these factors have lingering effects on post-transplant eGFR trajectory remains unclear. We characterized pre- and post-transplant eGFR trajectories in pediatric kidney transplant recipients by their pre-kidney replacement therapy (KRT) risk factors. METHODS: We studied eGFR trajectories before KRT initiation and after transplantation among Chronic Kidney Disease in Children (CKiD) Study participants. We used mixed-effects models to compare pre-KRT versus post-transplant eGFR trajectories within individual participants by 7 pre-KRT risk factors: glomerular/non-glomerular etiology, race, preemptive transplant, proteinuria, albuminuria, and systolic/diastolic blood pressure (SBP/DBP). RESULTS: We analyzed 1602 pre-KRT and 592 post-transplant eGFR measurements from 246 transplant recipients. Mean annual eGFR decline was decreased from 18.0% pre-KRT (95%CI, 16.1-19.8) to 5.0% post-transplant (95%CI, 3.3-6.7). All 7 pre-KRT risk factors showed strong associations with faster pre-KRT eGFR decline, but not with post-transplant eGFR decline; only albuminuria, high SBP, and high DBP reached statistical significance with notably attenuated associations. In our multivariable model of the pre-KRT risk factors, post-transplant eGFR decline was more rapid only when albuminuria and high SBP were both present. CONCLUSIONS: eGFR decline substantially slows down after transplant even among children with rapidly progressing forms of CKD. Nonetheless, those who had albuminuria and high SBP before KRT might continue to show faster eGFR decline after transplant, specifically when both risk factors were present. This subgroup might benefit from intensive pre-transplant management for at least one of the two risk factors. A higher resolution version of the Graphical abstract is available as Supplementary information.

Evidence of increased vascular stiffness and left ventricular hypertrophy in children with cystic kidney disease.

BACKGROUND: Cardiovascular disease (CVD) is the most common cause of mortality in chronic kidney disease (CKD). Children with early-onset CKD arguably experience the greatest lifetime CVD burden. We utilized data from the Chronic Kidney Disease in Children Cohort Study (CKiD) to evaluate two pediatric CKD cohorts: congenital anomalies of the kidney and urinary tract (CAKUT) and cystic kidney disease for CVD risks and outcomes. METHODS: CVD risk factors and outcomes including blood pressures, left ventricular hypertrophy (LVH), left ventricular mass index (LVMI), and ambulatory arterial stiffness index (AASI) scores were evaluated. RESULTS: Forty-one patients in the cystic kidney disease group were compared to 294 patients in the CAKUT group. Cystic kidney disease patients had higher cystatin-C levels, despite similar iGFR. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) indexes were higher in the CAKUT group, but a significantly higher proportion of cystic kidney disease patients was on anti-hypertensive medications. Cystic kidney disease patients had increased AASI scores and a higher incidence of LVH. CONCLUSIONS: This study provides a nuanced analysis of CVD risk factors and outcomes including AASI and LVH in two pediatric CKD cohorts. Cystic kidney disease patients had increased AASI scores, higher incidence of LVH, and higher rates of anti-hypertensive medication use which could imply a greater burden of CVD despite similar GFR. Our work suggests that additional mechanisms may contribute to vascular dysfunction in cystic kidney disease, and that these patients may need additional interventions to prevent the development of CVD. A higher resolution version of the Graphical abstract is available as Supplementary information.

Hyperkalemia in pediatric chronic kidney disease.

BACKGROUND: While hyperkalemia is well described in adult chronic kidney disease (CKD), large studies evaluating potassium trends and risk factors for hyperkalemia in pediatric CKD are lacking. This study aimed to characterize hyperkalemia prevalence and risk factors in pediatric CKD. METHODS: Cross-sectional analysis of Chronic Kidney Disease in Children (CKiD) study data evaluated median potassium levels and percentage of visits with hyperkalemia (K ≥5.5 mmoL/L) in relation to demographics, CKD stage, etiology, proteinuria, and acid-base status. Multiple logistic regression was used to identify risk factors for hyperkalemia. RESULTS: One thousand and fifty CKiD participants with 5183 visits were included (mean age 13.1 years, 62.7% male, 32.9% self-identifying as African American or Hispanic). A percentage of 76.6% had non-glomerular disease, 18.7% had CKD stage 4/5, 25.8% had low CO2, and 54.2% were receiving ACEi/ARB therapy. Unadjusted analysis identified a median serum potassium level of 4.5 mmol/L (IQR 4.1-5.0, p <0.001) and hyperkalemia in 6.6% of participants with CKD stage 4/5. Hyperkalemia was present in 14.3% of visits with CKD stage 4/5 and glomerular disease. Hyperkalemia was associated with low CO2 (OR 7.72, 95%CI 3.05-19.54), CKD stage 4/5 (OR 9.17, 95%CI 4.02-20.89), and use of ACEi/ARB therapy (OR 2.14, 95%CI 1.36-3.37). Those with non-glomerular disease were less frequently hyperkalemic (OR 0.52, 95%CI 0.34-0.80). Age, sex, and race/ethnicity were not associated with hyperkalemia. CONCLUSIONS: Hyperkalemia was observed more frequently in children with advanced stage CKD, glomerular disease, low CO2, and ACEi/ARB use. These data can help clinicians identify high-risk patients who may benefit from earlier initiation of potassium-lowering therapies. A higher resolution version of the Graphical abstract is available as Supplementary information.

Longitudinal changes in uric acid concentration and their relationship with chronic kidney disease progression in children and adolescents.

BACKGROUND: Elevated serum uric acid concentration is a risk factor for CKD progression. Its change over time and association with CKD etiology and concomitant changes in estimated glomerular filtration rate (eGFR) in children and adolescents are unknown. METHODS: Longitudinal study of 153 children/adolescents with glomerular (G) and 540 with non-glomerular (NG) etiology from the CKD in Children (CKiD) study. Baseline serum uric acid, change in uric acid and eGFR over time, CKD etiology, and comorbidities were monitored. Adjusted linear mixed-effects regression models quantified the relationship between within-person changes in uric acid and concurrent within-person changes in eGFR. RESULTS: Participants with stable uric acid over follow-up had CKD progression which became worse for increased baseline uric acid (average annual percentage changes in eGFR were - 1.4%, - 7.7%, and - 14.7% in those with G CKD with baseline uric acid < 5.5 mg/dL, 5.5 - 7.5 mg/dL, and > 7.5 mg/dL, respectively; these changes were - 1.4%, - 4.1%, and - 8.6% in NG CKD). Each 1 mg/dL increase in uric acid over follow-up was independently associated with significant concomitant eGFR decreases of - 5.7% (95%CI - 8.4 to - 3.0%) (G) and - 5.1% (95%CI - 6.3 to - 4.0%) (NG) for those with baseline uric acid < 5.5 mg/dL and - 4.3% (95%CI - 6.8 to - 1.6%) (G) and - 3.3% (95%CI - 4.1 to - 2.6%) (NG) with baseline uric acid between 5.5 and 7.5 mg/dL. CONCLUSIONS: Higher uric acid levels and increases in uric acid over time are risk factors for more severe progression of CKD in children and adolescents. A higher resolution version of the Graphical abstract is available as Supplementary information.

Associations of body mass index (BMI) and BMI change with progression of chronic kidney disease in children.

BACKGROUND: Obesity is prevalent among children with chronic kidney disease (CKD) and is associated with cardiovascular disease and reduced quality of life. Its relationship with pediatric CKD progression has not been described. METHODS: We evaluated relationships between both body mass index (BMI) category (normal, overweight, obese) and BMI z-score (BMIz) change on CKD progression among participants of the Chronic Kidney Disease in Children study. Kaplan-Meier survival curves and multivariable parametric failure time models depict the association of baseline BMI category on time to kidney replacement therapy (KRT). Additionally, the annualized percentage change in estimated glomerular filtration rate (eGFR) was modeled against concurrent change in BMIz using multivariable linear regression with generalized estimating equations which allowed for quantification of the effect of BMIz change on annualized eGFR change. RESULTS: Participants had median age of 10.9 years [IQR: 6.5, 14.6], median eGFR of 50 ml/1.73 m2 [IQR: 37, 64] and 63% were male. 160 (27%) of 600 children with non-glomerular and 77 (31%) of 247 children with glomerular CKD progressed to KRT over a median of 5 years [IQR: 2, 8]. Times to KRT were not significantly associated with baseline BMI category. Children with non-glomerular CKD who were obese experienced significant improvement in eGFR (+ 0.62%; 95% CI: + 0.17%, + 1.08%) for every 0.1 standard deviation concurrent decrease in BMI. In participants with glomerular CKD who were obese, BMIz change was not significantly associated with annualized eGFR change. CONCLUSION: Obesity may represent a target of intervention to improve kidney function in children with non-glomerular CKD. A higher resolution version of the Graphical abstract is available as Supplementary information.

Association of clinical characteristics with urine uromodulin in children with chronic kidney disease.

BACKGROUND: Uromodulin is the most abundant protein in the urine of healthy adults, and higher urine concentrations mark better tubular health. Greater kidney size and function are predictors of higher uromodulin levels in adults. Urine uromodulin has not yet been studied in children with chronic kidney disease (CKD). Thus, we sought to determine the relationship between age and kidney function with urine uromodulin levels in children with CKD. METHODS: In the CKD in Children (CKiD) cohort, we utilized multivariable linear regression to evaluate the relationship of age and eGFR with urine uromodulin levels. The primary outcome was uromodulin indexed to urine creatinine (Umod/Cr, mg/g), which was log2-transformed given its skewed distribution. RESULTS: Among 677 CKiD participants, the median age was 11.8 years (8.2-15.3), the median eGFR was 49 ml/min/1.73 m2 (37-63), the etiology of CKD was glomerular disease in 31%, and the median Umod/Cr level was 0.114 mg/g (0.045-0.226). In the multivariable models, each one-year older age was associated with 0.18 (12%) lower log2(Umod/Cr) and 0.20 (13%) lower log2(Umod/Cr) among those with non-glomerular and glomerular disease, respectively (p < 0.001). However, we did not find a statistically significant association between eGFR and Umod/Cr in either participants with non-glomerular or glomerular disease (p = 0.13 and p = 0.58, respectively). CONCLUSIONS: Among children with CKD, older age is significantly associated with lower Umod/Cr, independent of eGFR. Further studies are needed to comprehensively evaluate age-specific reference ranges for urine uromodulin and to evaluate the longitudinal relationship of uromodulin with both age and eGFR in children with CKD. A higher resolution version of the Graphical abstract is available as Supplementary information.