Iothalamate versus estimated GFR in a Hispanic-dominant pediatric renal transplant population

Performance of the various serum creatinine-based GFR estimating equations in pediatric kidney transplant recipients, stratified by age and CKD staging

BACKGROUND

Numerous equations are used to estimate glomerular filtration rate (eGFR), based on serum creatinine (SCr), demographic and anthropometric data, none established in pediatric kidney transplant recipients. This study aimed to validate the available SCr-based eGFR equations in comparison with a measured (mGFR), stratified by chronic kidney disease (CKD) stage and age at the time of testing.

METHODS

One hundred twenty-seven pediatric kidney transplant recipients with 411 mGFR values (plasma clearance of iothalamate) were enrolled in this retrospective study. The bias, precision, and accuracy (percentage of estimates within 10% and 30% of mGFR) of five SCr eGFR equations (original Schwartz, CKiDSCr equation, Pottel, Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)) were assessed.

RESULTS

Height-independent Pottel equation performed well across all the categories of age and CKD staging. CKiDSCr equation performed well in CKD stages II-V. The CKiDSCr equation had a lower bias in children < 15 years of age, while MDRD and CKD-EPI equations had less bias in children > 15 years. Overall, both the Pottel and CKiDSCr equations had high accuracy (80%) and low bias (< 5 ml/min/1.73 m²). In contrast, the original Schwartz, MDRD, and CKD-EPI equations displayed high bias and low precision/accuracy.

CONCLUSIONS

Given their low bias and high accuracy across ages and CKD stages, the Pottel or the CKiDSCr equation is better to assess eGFR in pediatric kidney transplant recipients. The Pottel equation outperformed other eGFR equations in adolescents.

Validation of serum creatinine-based formulae in pediatric renal transplant recipients

BackgroundAccurate monitoring of kidney function is important post-renal transplant; however, the routine use of measured glomerular filtration rate (GFR) or addition of newer serum markers is prohibitively expensive for routine clinical use, especially in children. We validated the modified Schwartz formula in pediatric renal transplant recipients across a range of demographic and clinical characteristics.MethodsIn a retrospective cohort study with nested cross-sectional analysis, we compared 505 measurements of estimated GFR using serum creatinine to simultaneous diethylenetriaminepentaacetic acid (DTPA) nuclear GFR (nGFR) measurements from 173 pediatric kidney transplant recipients who were < 18 years of age from 1 January 2001 to 31 December 2012 accounting for repeated measures.ResultsAmong 173 children, 62% were males, 85% with nGFR of ≥60 ml/min/1.73 m², and the median age at transplant was 13.6 years (interquartile range 8.3-16 years). Overall, the modified Schwartz and Pottel formulae had better bias (0.07 and -0.03 ml/min/1.73 m², respectively) and accuracy within 30% (both 84.4%) in comparison to Lyon and Zappitelli formulae. The 30% accuracy varied for girls and children <5 and >15 years.ConclusionModified Schwartz is a practical, non-invasive, and a valid bedside tool that provides a valid measurement of GFR in pediatric kidney transplant recipients.

Relationships of Measured Iohexol GFR and Estimated GFR With CKD-Related Biomarkers in Children and Adolescents

BACKGROUND

2 valid and reliable estimated glomerular filtration rate (GFR) equations for the pediatric population have been developed from directly measured GFR data in the Chronic Kidney Disease in Children (CKiD) cohort: the full CKiD and bedside CKiD equations. Although adult GFR estimating equations replicate relationships of measured GFR with biomarkers, it is unclear whether similar patterns exist among children and adolescents with chronic kidney disease (CKD).

STUDY DESIGN

Prospective cohort study in children and adolescents.

SETTINGS & PARTICIPANTS

730 participants contributed 1,539 study visits.

PREDICTORS

Measured GFR by plasma iohexol disappearance (mGFR), estimated GFR by the full CKiD equation (eGFR_CKiDfull; based on serum creatinine, cystatin C, serum urea nitrogen, height, and sex), and estimated GFR by the bedside CKiD equation (eGFR_CKiDbed; calculated as 41.3 × height [m]/serum creatinine [mg/dL]) were predictors of CKD-related biomarkers. Deviations of mGFR from eGFR_CKiDfull and deviations of eGFR_CKiDfull from eGFR_CKiDbed from linear regressions (ie, residuals) were included in bivariate analyses.

OUTCOMES & MEASUREMENTS

CKD-related biomarkers included values for urine protein-creatinine ratio, blood hemoglobin, serum phosphate, bicarbonate, potassium, systolic and diastolic blood pressure z scores, and height z scores.

RESULTS

The median age of 730 participants with CKD was 12.5 years, with median mGFR, eGFR_CKiDfull, and eGFR_CKiDbed of 51.8, 54.0, and 53.2mL/min/1.73m², respectively. eGFR_CKiDfull demonstrated as strong or stronger associations with CKD-related biomarkers than mGFR; eGFR_CKiDbed associations were significantly attenuated (ie, closer to the null). Residual information in mGFR did not substantially increase explained variability. eGFR_CKiDbed estimated faster GFR decline relative to mGFR and eGFR_CKiDfull.

LIMITATIONS

Simple linear summaries of biomarkers may not capture nonlinear associations.

CONCLUSIONS

eGFR_CKiDfull closely approximated mGFR to describe relationships with CKD-severity indicators and progression in this pediatric CKD population. eGFR_CKiDbed offered similar inferences, but associations were attenuated and rate of progression was overestimated. The eGFR_CKiDfull equation from 2012 is preferred for pediatric research purposes.

Accuracy of different equations in estimating GFR in pediatric kidney transplant recipients

BACKGROUND AND OBJECTIVE

The knowledge of renal function is crucial for the management of pediatric kidney transplant recipients. In this population, the most commonly used plasma creatinine (PCr)-based or cystatin C (CystC)-based GFR-predicting formulas may underperform (e.g., corticosteroids and trimethoprim may affect PCr concentration, whereas prednisone and calcineurin inhibitors may affect CystC concentration). This study evaluated the performance of six formulas in pediatric kidney transplant recipients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study used PCr-based formulas (bedside Schwartz, Schwartz-Lyon), CystC-based formulas (Hoek, Filler), and combined PCr-CystC-based formulas (CKD in Children [CKiD] 2012 and Zappitelli). The performance of these formulas was compared using inulin clearance as reference and assessed according to CKD stages in a historical cohort that included 73 pediatric kidney transplant recipients (199 measurements). The ability of the formulas to identify GFRs<60, <75, and <90 ml/min per 1.73 m(2) was assessed.

RESULTS

At measured GFR (mGFR) ≥90 ml/min per 1.73 m(2) (nine patients; 23 measurements), the Zappitelli formula had the highest 30% accuracy (P30) (95% [95% confidence interval (95% CI), 87% to 100%]) and the bedside Schwartz had the highest 10% accuracy (P10) (56% [95% CI, 32% to 72%]). At mGFR≥60 and <90 ml/min per 1.73 m(2) (22 patients; 91 measurements), all formulas had P30 values >80%. However, only the CKiD 2012 formula had a P10 value >50%. At mGFR<60 ml/min per 1.73 m(2) (42 patients; 85 measurements), the CKiD 2012 and Schwartz-Lyon formulas had the highest P10 (45% [95% CI, 34% to 55%] and 43% [95% CI, 33% to 54%]) and P30 (90% [95% CI, 84% to 97%] and 91% [95% CI, 86% to 98%]). All studied equations except Hoek and Filler had areas under the receiver-operating characteristic curves significantly >90% in discriminating patients with renal dysfunction at various CKD stages (GFR<60, <75, and <90 ml/min per 1.73 m(2)).

CONCLUSIONS

In pediatric kidney transplant recipients, the CKiD 2012 formula had the best performance at mGFRs<90 ml/min per 1.73 m(2). CystC-based formulas were not superior to PCr-based formulas.