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.

Cyclohexanone Exposure in Children on Extracorporeal Membrane Oxygenation Support

The aim of this study was to determine if plasma cyclohexanone and metabolites are associated with clinical outcomes of children on extracorporeal membrane oxygenation (ECMO) support. We performed a secondary analysis of a prospective observational study of children on ECMO support at two academic centers between July 2010 and June 2015. We measured plasma cyclohexanone and metabolites on the first and last days of ECMO support. Unfavorable outcome was defined as in-hospital death or discharge Pediatric Cerebral Performance Category score > 2 or decline ≥ 1 from baseline. Among 90 children included, 49 (54%) had unfavorable outcome at discharge. Cyclohexanediol, a cyclohexanone metabolite, was detected in all samples and at both time points; concentrations on the first ECMO day were significantly higher in those with unfavorable versus favorable outcome at hospital discharge (median, 5.7 ng/µl; interquartile range [IQR], 3.3-10.6 ng/µl vs. median, 4.2 ng/µl; IQR, 1.7-7.3 ng/µl; p = 0.04). Twofold higher cyclohexanediol concentrations on the first ECMO day were associated with increased risk of unfavorable outcome at hospital discharge (multivariable-adjusted hazard ratio [HR], 1.24 [95% CI, 1.05-1.48]). Higher cyclohexanediol concentrations on the first ECMO day were not significantly associated with new abnormal neuroimaging or 1-year Vineland Adaptive Behavior Scales-II score < 85 or death among survivors.

Variability in CKD Biomarker Studies: Soluble Urokinase Plasminogen Activator Receptor (suPAR) and Kidney Disease Progression in the Chronic Kidney Disease in Children (CKiD) Study

Rationale & Objective

Biomarker studies are important for generating mechanistic insight and providing clinically useful predictors of chronic kidney disease (CKD) progression. However, variability across studies can often muddy the evidence waters. Here we evaluated real-world variability in biomarker studies using two published studies, independently conducted, of the novel plasma marker soluble urokinase-type plasminogen activator receptor (suPAR) for predicting CKD progression in children with CKD.

Study Design

A comparison of 2 prospective cohort studies.

Setting & Participants

541 children from the Chronic Kidney Disease in Children (CKiD) study, median age 12 years, median glomerular filtration rate (GFR) of 54 mL/min/1.73m².

Outcome

The first occurrence of either a 50% decline in GFR from baseline or incident end-stage kidney disease.

Analytical Approach

The suPAR plasma marker was measured using the Quantikine ELISA immunoassay in the first study and Meso Scale Discovery (MSD) platform in the second. The analytical approaches varied. We used suPAR data from the 2 assays and mimicked each analytical approach in an overlapping subset.

Results

We found that switching assays had the greatest impact on inferences, resulting in a 38% to 66% change in the magnitude of the effect estimates. Covariate and modeling choices resulted in an additional 8% to 40% variability in the effect estimate. The cumulative variability led to different inferences despite using a similar sample of CKiD participants and addressing the same question.

Limitations

The estimated variability does not represent optimal repeatability but instead illustrates real-world variability that may be present in the CKD biomarker literature.

Conclusions

Our results highlight the importance of validation, avoiding conclusions based on P value thresholds, and providing comparable metrics. Further transparency of data and equal weighting of negative and positive findings in explorations of novel biomarkers will allow investigators to more quickly weed out less promising biomarkers.

Correction to: Mode of initial renal replacement therapy and transplant outcomes in the chronic kidney disease in children (CKiD) study

The original version of this article unfortunately contained a mistake.

Mode of initial renal replacement therapy and transplant outcomes in the chronic kidney disease in children (CKiD) study

BACKGROUND

Kidney transplant is the renal replacement therapy (RRT) of choice for children with end stage kidney disease (ESKD). Only 21.3% of children who initiate RRT receive a preemptive kidney transplant (PKT). We characterized the transition to RRT in children in the CKiD cohort including the prevalence of dialysis as first RRT vs. PKT and graft survival.

METHODS

258 children enrolled in CKiD have initiated RRT, and 202 had post-RRT initiation data collected through phone or in-person follow-up. Characteristics by first RRT modality were compared using Chi-square and Kruskal-Wallis tests. Parametric-accelerated failure time models were fit for transplantation. Graft failure was characterized using Kaplan-Meier methods and log rank tests.

RESULTS

Sixty-one percent received dialysis as first RRT modality and 39% PKT. Those with PKT were less likely to have glomerular disease and to be African-American, and had higher household-income. African-American subjects were nearly twice as likely to undergo dialysis prior to transplant. Those with a living donor and a college-educated mother had 40%-decreased odds of being dialysis experienced. Children with PKT were more likely to receive a living donor transplant. Only 5% of PKT subjects had graft failure by 4 years compared to 16% of those initially treated with dialysis (p = 0.092); however, after adjustment the effect of dialysis exposure was attenuated (p = 0.206).

CONCLUSION

CKiD subjects undergo PKT more often compared to nationally-reported rates, and are more likely to receive a kidney transplant within 1 year of starting dialysis. African-American race and lower household-income are associated with decreased access to PKT.

Plasma Soluble Urokinase Plasminogen Activator Receptor (suPAR) and CKD Progression in Children

RATIONALE & OBJECTIVE

Soluble urokinase plasminogen activator receptor (suPAR) is a novel biomarker associated with incident chronic kidney disease (CKD) and has been identified as an independent risk factor for CKD progression in children, although these findings remain preliminary, limited to a single point in time, and unreplicated in pediatric cohorts.

STUDY DESIGN

Prospective longitudinal cohort study.

SETTING & PARTICIPANTS

565 participants aged 1 to 16 years enrolled in the Chronic Kidney Disease in Children (CKiD) Study.

EXPOSURE

Plasma suPAR levels, categorized by quartiles, measured at study entry and a 6-month follow-up interval.

OUTCOME

CKD progression, defined as the initiation of kidney replacement therapy (dialysis or transplantation) or >50% decline in estimated glomerular filtrate rate (eGFR).

ANALYTIC APPROACH

Associations between plasma suPAR quartiles and risk for CKD progression were estimated using lognormal survival models, adjusting for potential confounders.

RESULTS

Participants in the highest suPAR quartile experienced 54% faster progression compared with the lowest quartile after adjustment for demographic and traditional CKD risk factors (P < 0.001). Addition of eGFR to the model attenuated the risk, although those in the highest quartile experienced 33% faster progression compared with the lowest quartile (P = 0.008). Plasma suPAR levels showed little change over 6 months.

LIMITATIONS

Potential for residual confounding, reliance on observational data, relatively fewer patients with higher eGFRs for subgroup analysis.

CONCLUSIONS

Higher suPAR levels are associated with shorter time to kidney replacement therapy or halving of eGFR in children with CKD. This association is attenuated slightly with inclusion of eGFR in regression modeling but remains a significant association for participants with the highest suPAR levels.

Breastfeeding and pelvic floor disorders one to two decades after vaginal delivery

BACKGROUND

Postpartum recovery from pelvic floor trauma associated with vaginal delivery may be impaired by the transient hypoestrogenic state associated with breastfeeding.

OBJECTIVE

The aim of our study was to examine the association between exclusive breastfeeding and pelvic floor disorders 1-2 decades after the first vaginal delivery. We hypothesize that compared with women who did not breastfeed following vaginal delivery, women who breastfeed would have a higher proportion of pelvic floor disorders s, and those women who practiced sustained exclusive/unsupplemented breastfeeding would have the highest proportion.

STUDY DESIGN

This is a secondary analysis of the Mothers' Outcomes After Delivery study, a prospective cohort study of pelvic floor disorders after childbirth. Participants were recruited 5-10 years after their first delivery and followed up annually for up to 9 years. This analysis focused on participants who experienced at least 1 vaginal delivery. Each participant completed a self-administered questionnaire regarding breastfeeding. Based on questionnaire responses, breastfeeding status was classified into 3 ordinal categories: unexposed (did not breastfeed or breastfed <1 week); limited exclusive breastfeeding (breastfed without supplementation for ≥1 week but <12 weeks); and sustained exclusive breastfeeding (unsupplemented breastfeeding ≥12 weeks). Our primary outcomes of interest were the proportions of stress urinary incontinence, anal incontinence, and pelvic organ prolapse. The outcomes of interest were defined using the Epidemiology of Prolapse and Incontinence Questionnaire and the Pelvic Organ Prolapse Quantification Examination at enrollment and annually for up to 9 years thereafter. Additionally, a subanalysis examined the relationship between breastfeeding and anal incontinence in an obstetric anal sphincter injury-specific population. Generalized estimating equations were utilized to determine the relationship between breastfeeding and the outcomes of interest.

RESULTS

Among 705 women, 189 (27%) were classified as unexposed, 145 (20%) were categorized as limited exclusive breastfeeding, and the remaining 371 women (53%) met our definition of sustained exclusive breastfeeding. Median follow-up was 5 years, contributing to a total of 3079 person years. The proportion of each pelvic floor disorder, based on 3079 person-years of follow-up was: stress urinary incontinence (27%), pelvic organ prolapse (20%), or anal incontinence (25%). Using generalized estimating equations adjusting for race, education, parity, and body mass index, sustained exclusive breastfeeding was not significantly associated with stress urinary incontinence (adjusted odds ratio, 0.82, 95% confidence interval, 0.55-1.23), pelvic organ prolapse (adjusted odds ratio, 0.78, 95% confidence interval, 0.49-1.26), and anal incontinence (adjusted odds ratio, 0.67, 95% confidence interval, 0.44-1.00). Regarding our obstetric anal sphincter injury subanalysis, 123 women within our cohort experienced obstetric anal sphincter injuries at delivery. Anal incontinence was reported in 32% of these women. However, there was no observed relationship between breastfeeding and the development of anal incontinence during study follow-up in this population.

CONCLUSION

Breastfeeding after vaginal childbirth was not associated with the development of stress urinary incontinence, pelvic organ prolapse, or anal incontinence 1-2 decades after the first vaginal delivery.

Longitudinal changes in pelvic floor muscle strength among parous women

BACKGROUND

There is limited knowledge of the effects of time on change in pelvic floor muscle strength after childbirth.

OBJECTIVE

The objectives of this study were to estimate the change in pelvic floor muscle strength in parous women over time and to identify maternal and obstetric characteristics associated with the rate of change.

STUDY DESIGN

This is an institutional review board-approved prospective cohort study of parous women. Participants were recruited 5-10 years after first delivery and followed annually. Pelvic floor muscle strength (peak pressure with voluntary contraction) was measured at 2 annual visits approximately 4 years apart with the use of a perineometer. We calculated the change in peak pressures, which were standardized per 5-year interval. Linear regression was used to identify maternal and obstetric characteristics that are associated with the rate of change in peak pressure. The obstetric variable of greatest interest was delivery group. Participants were classified into 3 delivery groups (considering all deliveries for each multiparous woman). Delivery categories included cesarean only, at least 1 vaginal birth but no forceps-assisted deliveries, and at least 1 forceps-assisted vaginal birth. Statistical analysis was completed with statistical software.

RESULTS

Five hundred forty-three participants completed 2 perineometer measurements with a median 4 years between measures (interquartile range, 3.1-4.8). At initial measurement, women were, on average, 40 years old and 8 years from first delivery. Initial strength was higher in participants who delivered all their children by cesarean (38.5 cm H₂O) as compared with women with any vaginal non-forceps delivery (26.0 cm H₂O) or vaginal forceps delivery (13.5 cm H₂O; P<.001). There was a strong correlation between the first and second perineometry measurement (r=0.84). Median change in pelvic floor muscle strength was small at 1.2 cm H₂O per 5 years (interquartile range, -5.6, 9.9 cm H₂O). In multivariable analysis, women who delivered by cesarean only demonstrated almost no change in strength over 5 years (0.2 increase cm H₂O per 5 years); those who experienced at least 1 vaginal or vacuum delivery increased strength (4.8 cm H₂O per 5 years) as did women with at least 1 forceps delivery (5.0 cm H₂O per 5 years). Additionally, obese women had a significant reduction in strength (-3.1 cm H₂O per 5 years) compared with normal weight participants (0.2 cm H₂O per 5 years).

CONCLUSION

Among parous women, pelvic muscle strength increased minimally over time with an average change of 1.2 cm H₂O per 5 years; change in strength was associated with mode of delivery and obesity.