Creatinine-based GFR-estimating equations in children with overweight and obesity

Comparison of different eGFR formulas to measured glomerular filtration rate using iohexol in children and adolescents with mild chronic kidney disease

Estimated glomerular filtration rate (eGFR) based on different formulas is commonly used as a bedside tool to assess kidney function in children and young adults. The purpose of this study was to perform a measurement of glomerular filtration rate (mGFR) in children with chronic kidney disease (CKD) with a standard 5-point protocol using iohexol clearance and compare it to a simplified protocol for mGFR determination and to some of the most commonly used eGFR formulas. A 5-point standard protocol using iohexol clearance was used for determination of mGFR in 50 children with mild stages of CKD. The result was compared to 2- and 3-point sampling protocol as well as with some standard children eGFR formulas. We calculated the prediction performance for eGFR formulas to distinguish CKD1 and CKD 2 stages, formulas' accuracy, and cutoff values. Data were prospectively collected. All eGFR formulas exhibited a statistically significant positive correlation with mGFR. The best correlation was found with CKID2012 eGFR formula and with cystatin C-based eGFR formulas. The correlation between standard and simplified protocols for mGFR determination was also strong, while creatinine clearance did not prove to be a reliable method for estimating GFR. The error distribution with simplified protocols was not dispersed. The prediction value was strong for CKID2012 and bedside Schwartz formula. Conclusion: Fewer sampling points can be safely used for measuring GFR in children. eGFR formulas that are not based solely on creatinine should be considered more often in GFR estimation. What is Known? • Iohexol clearance is an established method of measuring GFR in children and adolescents using different protocols. • Estimating GFR in children and adolescents is troublesome and is done using different formulas with anthropometric and biochemical markers in children and adolescents. What is New? • Iohexol measurement with two or three blood withdrawals can reliably distinguish between CKD1 and CKD2 patients. • eGFR formulas have moderate reliability to predict distinguish between CKD1 and CKD2 patients, of which CKID2012 and bedside Schwartz formula were the most accurate in our study.

The evaluation of kidney function estimation during lifestyle intervention in children with overweight and obesity

BACKGROUND

Children with overweight and obesity are at risk for developing chronic kidney disease (CKD). During lifestyle adjustment, the first step in the treatment of childhood obesity, body proportions are likely to change. The aim of this study was to examine how lifestyle intervention affects creatinine-based kidney function estimation in children with overweight and obesity.

METHODS

This longitudinal lifestyle intervention study included 614 children with overweight and obesity (mean age 12.17 ± 3.28 years, 53.6% female, mean BMI z-score 3.32 ± 0.75). Loss to follow-up was present: 305, 146, 70, 26, and 10 children were included after 1, 2, 3, 4, and 5 (about yearly) follow-up visits, respectively. Serum creatinine (SCr) was rescaled using Q-age and Q-height polynomials.

RESULTS

At baseline, 95-97% of the children had a SCr/Q-height and SCr/Q-age in the normal reference range [0.67-1.33]. SCr/Q significantly increased each (about yearly) follow-up visit, and linear mixed regression analyses demonstrated slopes between 0.01 and 0.04 (corresponding with eGFR FAS reduction of 1.1-4.1 mL/min/1.73 m2) per visit. BMI z-score reduced in both sexes and this reduction was significantly higher in males. No correlation between change in rescaled SCr and BMI z-score reduction could be demonstrated.

CONCLUSIONS

Rescaled serum creatinine (SCr/Q) slightly increases during multidiscipline lifestyle intervention in this cohort of children with overweight and obesity. This effect seems to be independent from change in BMI z-score. Whether this minor decrease in estimated kidney function has clinical consequences in the long term remains to be seen in trials with a longer follow-up period.

CLINICAL TRIAL REGISTRATION

ClinicalTrial.gov; Registration Number: NCT02091544.

Estimated glomerular filtration rate: applicability of creatinine-based equations in African children

BACKGROUND

The Schwartz equation is the most widely used serum creatinine (SCr)-based formula to estimate the glomerular filtration rate (GFR) in children of European descent, but whether this applies to African children is unclear.

METHODS

In a cross-sectional study, 513 apparently healthy African children aged 6 to 16 years were randomly recruited in school area of Kinshasa, the Democratic Republic of Congo (DRC). SCr was measured using calibrated enzymatic method. SCr was normalized using Q-values designed for European descent children, due to the absence of Q-values for African children. Commonly used eGFR equations were applied in this population.

RESULTS

Normalization of SCr using Q-values for European descent children was effective in this cohort. The majority of African children (93.4%) have normalized SCr (SCr/Q) values within the reference interval (0.67-1.33) of children of European descent. The bedside-Schwartz equation was associated with significant age and sex dependency. However, the FAS-Age formula showed no sex and age dependency. The new CKiDU25 equation did not show a significant sex dependency. The recently introduced EKFC and LMR18 equations also showed no age and sex dependency, although the distribution of eGFR-values was not symmetrical. On the other hand, the FAS-Height and the Schwartz-Lyon equations showed significant sex dependency but no age dependency.

CONCLUSIONS

The reference interval for SCr designed for European descent children can be applied to African children. Of all the equations studied, FAS-Age performed best and is most suitable because no height measurements are required. Establishment of specific Q-values for the widespread Jaffe-measured creatinine in Africa can further broaden applicability.

[Current clinical application of glomerular filtration rate assessment methods in pediatric populations]

Glomerular filtration rate (GFR) is a critical indicator of renal function assessment, which exhibits age-dependency in children and may differ from adults under various disease conditions. In recent years, there has been a growing focus on GFR among scholars, with an increasing number of clinical studies dedicated to refining and optimizing GFR estimation to span all pediatric age groups. However, the methods and assessment equations for estimating GFR may vary under different disease conditions, affecting the accuracy and applicability of assessments. This article reviews the peculiarities of renal function in children, explores GFR measurement methods, and evaluates the application of various GFR assessment equations in pediatric clinical practice, providing a reference for clinical assessment of renal function in children.

Prevalence and associated factors of impaired kidney functions among children and adolescents in India: insights from the Comprehensive National Nutrition Survey (CNNS) 2016-18

BACKGROUND

Chronic kidney disease (CKD) is a significant public health problem. The burden of CKD in children and adolescents in India is not well described. We used data from the recent Comprehensive National Nutrition Survey (CNNS) to estimate the prevalence of impaired kidney function (IKF) and its determinants in children and adolescents between the ages of 5 and 19.

METHODS

CNNS 2016-18 adopted a multi-stage sampling design using probability proportional to size sampling procedure after geographical stratification of urban and rural areas. Serum creatinine was tested once in 24,690 children and adolescents aged 5-19 years. The estimated glomerular filtration rate (eGFR) was derived using the revised Schwartz equation. The eGFR value below 60 ml/min/1.73 m2 is defined as IKF. Bivariate analysis was done to depict the weighted prevalence, and multivariable logistic regression examined the predictors of IKF.

RESULTS

The mean eGFR in the study population was 113.3 + 41.4 mL/min/1.73 m2. The overall prevalence of IKF was 4.9%. The prevalence in the 5-9, 10-14, and 15-19 year age groups was 5.6%, 3.4% and 5.2%, respectively. Regression analysis showed age, rural residence, non-reserved social caste, less educated mothers, Islam religion, children with severe stunting or being overweight/obese, and residence in Southern India to be predictors of IKF.

CONCLUSIONS

The prevalence of IKF among children and adolescents in India is high compared to available global estimates. In the absence of repeated eGFR-based estimates, these nationally representative estimates are intriguing and call for further assessment of socio-demographic disparities, genetics, and risk behaviours to have better clinical insights and public health preparedness.

Extending the cystatin C based EKFC-equation to children - validation results from Europe

BACKGROUND

A new cystatin C based European Kidney Function Consortium (EKFCCysC) equation was recently developed for adults, using the same mathematical form as the previously published full age spectrum creatinine based EKFC-equation (EKFCCrea). In the present study the cystatin C based EKFC-equation is extended to children, by defining the appropriate cystatin C rescaling factor QCysC.

METHODS

Rescaling factor QCysC for cystatin C was defined as: a) 0.83 mg/L, exactly as it was defined for young adults in the adult equation, and b) a more complex QCysC-age relationship based on 4th degree cystatin C-age polynomials after evaluation of data from Uppsala, Stockholm and Canada and aggregated data from Germany. The EKFCCysC equation was then validated in an independent dataset in European children (n = 2,293) with measured GFR, creatinine, cystatin C, age, height and sex available.

RESULTS

The EKFCCysC with the simple QCysC-value of 0.83 had a bias of -7.6 [95%CI -8.4;-6.5] mL/min/1.73 m2 and a P30-value of 85.8% [95%CI 84.4;87.3] equal to the EKFCCysC with the more complex 4th degree QCysC-value. The arithmetic mean of the EKFCCrea and EKFCCysC with the simple QCysC of 0.83 had a bias of -4.0 [95%CI -4.5;-3.1] mL/min/1.73 m2 and P30 of 90.4% [95%CI 89.2;91.6] similar to using the more complex 4th degree QCysC-polynomial.

CONCLUSION

Using exactly the same QCysC of 0.83 mg/L, the adult EKFCCysC can easily be extended to children, with some bias but acceptable P30-values. The arithmetic mean of EKFCCrea and EKFCCysC results in bias closer to zero and P30 slightly over 90%.

Childhood Obesity: Insight into Kidney Involvement

This review examines the impact of childhood obesity on the kidney from an epidemiological, pathogenetic, clinical, and pathological perspective, with the aim of providing pediatricians and nephrologists with the most current data on this topic. The prevalence of childhood obesity and chronic kidney disease (CKD) is steadily increasing worldwide, reaching epidemic proportions. While the impact of obesity in children with CKD is less pronounced than in adults, recent studies suggest a similar trend in the child population. This is likely due to the significant association between obesity and the two leading causes of end-stage renal disease (ESRD): diabetes mellitus (DM) and hypertension. Obesity is a complex, systemic disease that reflects interactions between environmental and genetic factors. A key mechanism of kidney damage is related to metabolic syndrome and insulin resistance. Therefore, we can speculate about an adipose tissue-kidney axis in which neurohormonal and immunological mechanisms exacerbate complications resulting from obesity. Adipose tissue, now recognized as an endocrine organ, secretes cytokines called adipokines that may induce adaptive or maladaptive responses in renal cells, leading to kidney fibrosis. The impact of obesity on kidney transplant-related outcomes for both donors and recipients is also significant, making stringent preventive measures critical in the pre- and post-transplant phases. The challenge lies in identifying renal involvement as early as possible, as it is often completely asymptomatic and not detectable through common markers of kidney function. Ongoing research into innovative technologies, such as proteomics and metabolomics, aims to identify new biomarkers and is constantly evolving. Many aspects of pediatric disease progression in the population of children with obesity still require clarification. However, the latest scientific evidence in the field of nephrology offers glimpses into various new perspectives, such as genetic factors, comorbidities, and novel biomarkers. Investigating these aspects early could potentially improve the prognosis of these young patients through new diagnostic and therapeutic strategies. Hence, the aim of this review is to provide a comprehensive exploration of the pathogenetic mechanisms and prevalent pathological patterns of kidney damage observed in children with obesity.

Sensitivity to Thyroid Hormones and Reduced Glomerular Filtration in Children and Adolescents with Overweight or Obesity

BACKGROUND

Reduced central sensitivity to thyroid hormones (THs) has been observed in euthyroid adults with reduced renal function. This topic is unexplored in young people with overweight or obesity (OW/OB).

OBJECTIVE

The aim of this study was to evaluate the association between sensitivity to TH and mild reduced estimated glomerular filtration rate (MReGFR) in euthyroid children and adolescents with OW/OB.

METHODS

Data of 788 euthyroid children and adolescents with OW/OB (aged 6-16 years), recruited from seven Italian centers for the care of OW/OB, were evaluated. Peripheral sensitivity to TH was estimated through the FT3/FT4 ratio, while central sensitivity was assessed by estimating TSH index (TSHI), thyrotroph T4 resistance index, thyroid feedback quantile-based index (TFQI), parametric thyroid feedback quantile-based index (PTFQI). MReGFR was defined by an eGFR value ≥60 and <90 mL/min/1.73 m2.

RESULTS

Subjects with MReGFR had significantly lower levels of FT3/FT4 ratio (0.43 ± 0.09 vs. 0.44 ± 0.10; p = 0.028) and higher levels of TSH (2.89 ± 1.00 vs. 2.68 ± 0.99; p = 0.019), TSHI (2.95 ± 0.45 vs. 2.85 ± 0.55; p = 0.031), TFQI [1.00 (0.98-1.00) versus 1.00 (0.97-1.00); p = 0.046], and PTFQI (0.66 ± 0.17 vs. 0.60 ± 0.23; p = 0.006) compared with individuals with normal eGFR. Odds ratio of MReGFR raised of 1.2-3.2-fold for each increase of 1 mIU/L in TSH, 1 unit in TSHI, and PTFQI, but not for FT3/FT4 ratio.

CONCLUSION

MReGFR is associated with reduced indices of central sensitivity to TH in euthyroid children and adolescents with OW/OB. This preliminary observation should be confirmed in prospective studies.

Estimated pediatric glomerular filtration rate presentation improves the detection rate of kidney impairment in children

BACKGROUND

Accurate interpretation of everyday laboratory work is crucial for the early detection of impaired kidney function. Bedside estimation of glomerular filtration rate (eGFR) in children is based on serum creatinine standardized for body mass, most commonly using the revised Schwartz equation using height. This study evaluates how data presentation affects the correct assessment of children's kidney function.

METHODS

In this survey-based study, 121 physicians treating children routinely in a tertiary hospital answered 11 clinical questions requiring assessment of kidney function based on serum creatinine with general (adult) or pediatric normal serum creatinine ranges, or by presented eGFR. The demographic data of the participants were collected.

RESULTS

Presenting eGFR values rather than the customary presentation of serum creatinine and anthropometric parameters more than quadrupled the number of physicians who accurately estimated pediatric kidney function; 38.8% of physicians correctly assessed kidney function when presented with eGFR values but misinterpreted it when equivalent creatinine values were presented (p < 0.001). Seniority, specialty, and self-reported frequency of pediatric kidney function assessment did not affect the interpretation.

CONCLUSIONS

Presenting physicians with calculated eGFR can dramatically improve the ability of the medical team to assess kidney function correctly in children. A higher resolution version of the Graphical abstract is available as Supplementary information.

Glomerular hyperfiltration: part 2-clinical significance in children

Glomerular hyperfiltration (GHF) is a phenomenon that can occur in various clinical conditions affecting the kidneys such as sickle cell disease, diabetes mellitus, autosomal dominant polycystic kidney disease, and solitary functioning kidney. Yet, the pathophysiological mechanisms vary from one disease to another and are not well understood. More so, it has been demonstrated that GHF may occur at the single-nephron in some clinical conditions while in others at the whole-kidney level. In this review, we explore the pathophysiological mechanisms of GHF in relation to various clinical conditions in the pediatric population. In addition, we discuss the role and mechanism of action of important factors such as gender, low birth weight, and race in the pathogenesis of GHF. Finally, in this current review, we further highlight the consequences of GHF in the progression of kidney disease.

Lipid metabolism and renal function markers in obese adolescents

AIM OF THE STUDY

To investigate the relationship of renal function markers and lipid metabolism parameters in obese adolescents.

MATERIAL AND METHODS

The study comprised 76 children aged 11-17 years, hospitalised due to: obesity (group I - 19 children) or obesity accompanied by obesity-induced hypertension (group II - 30 children) or normosthenic children with a diagnosed tension headaches (control group - 27 children). A subgroup with metabolic syndrome (MS - 16 children) was also separated. Renal function was assessed on the basis of: serum creatinine concentration, glomerular filtration rate estimated using Schwartz eqation (eGFR), determination of plasma and urinary neutrophil gelatinase-associated lipocalin and cystatin C. On the basis of statistical analysis, it was checked whether renal function markers depend on lipid metabolism parameters.

RESULTS

In the study groups mean creatinine concentrations were significantly higher and eGFR values significantly lower than in the control group, but they remained within norm. Differences in plasma and urinary neutrophil gelatinase-associated lipocalin concentrations were not significant. Mean cystatin C concentrations were significantly higher in the group of obese children. Multiple linear regression analysis showed that the most important predictor was: LDL-C for urinary neutrophil gelatinase-associated lipocalin (R2 = 0.42) and TG for eGFR (R2 = 0.44) concentrations in group I; cholesterol for creatinine concentrations in MS group (R2 = 0.44).

CONCLUSIONS

Renal function of the obese adolescents included in the study was normal and the associations with lipid metabolism were poorly expressed.

Relation between obesity-related comorbidities and kidney function estimation in children

BACKGROUND

The current childhood obesity pandemic is likely to result in an increased risk of chronic kidney disease (CKD) later in life. Correlations between obesity-related comorbidities and kidney function can be found, but it is unclear to what extent this is caused by bias due to different mathematical forms of the estimated glomerular filtration rate (eGFR) equations. The present study aimed to analyze correlations between obesity-related comorbidities and different eGFR equations and to investigate whether rescaled serum creatinine (SCr/Q) for sex and age or height might be an alternative biomarker for kidney function estimation.

METHODS

This cross-sectional cohort study included 600 children with overweight and obesity. Mean age was 12.20 ± 3.28 years, 53.5% were female, and mean BMI z-score was 3.31 ± 0.75. All children underwent a comprehensive assessment that included anthropometrical and blood pressure measurements, laboratory examination, air displacement plethysmography, and polysomnography. Qage and Qheight polynomials were used to rescale SCr and multiple creatinine-based eGFR equations were compared.

RESULTS

SCr/Q and almost all GFR estimations significantly correlated with a waist-to-hip ratio, fat mass, homeostasis model assessment for insulin resistance, and triacylglyceride, HDL cholesterol, alanine transaminase, and serum uric acid concentrations. Multiple correlations, however, were not confirmed by all equations, which suggests dependency on the mathematical form of the different eGFR equations.

CONCLUSIONS

Correlations between obesity-related comorbidities and creatinine-based eGFR are present in children with overweight and obesity, but depend to a large extent on the eGFR equation of choice. SCr/Q might be an alternative biomarker for assessing correlations between obesity-related comorbidities and kidney function in children with overweight and obesity. A higher resolution version of the Graphical abstract is available as Supplementary information.