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Abstract: SA-PO360

Validating CKiD U25 eGFR Equations for Differing Body Habitus

Session Information

  • Pediatric Nephrology - III
    November 04, 2023 | Location: Exhibit Hall, Pennsylvania Convention Center
    Abstract Time: 10:00 AM - 12:00 PM

Category: Pediatric Nephrology

  • 1900 Pediatric Nephrology


  • Pierce, Christopher B., Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, United States
  • Ng, Derek K., Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, United States
  • Warady, Bradley A., Children's Mercy Kansas City, Kansas City, Missouri, United States

Group or Team Name

  • Chronic Kidney Disease in Children Study.

The Chronic Kidney Disease in Children (CKiD) U25 eGFR equations provide unbiased estimates of glomerular filtration rate (eGFR) and strong levels of agreement with measured GFR (mGFR) for CKD patients 1-25 years old. However, the performance of these equations by body habitus has not been assessed.


Data were from the CKiD U25 validation set comprising 832 observations from 302 participants. Median age was 12 [IQR: 8,16] years and iohexol mGFR was 44 [32,61] mL/min/1.73m2. We evaluated three U25 equations: creatinine, cystatin C and the average of the two. Within BMI categories (underweight, normal weight, overweight, obese), we summarize agreement as mean bias (eGFR-mGFR) and percent of eGFR within 30% of mGFR (P30). Mean bias was calculated from a mixed effects model to account for multiple observations per participant.


All equations overestimated GFR in underweight subjects with the two cystatin C-based equations exhibiting statistically significant biases which persisted after adjusting for sex, age and GFR level. All equations underestimated GFR in overweight subjects but these biases were not significantly different than those in the normal weight subjects after adjustment. There was no bias observed in the obese category, suggesting this bias may not be a direct function of larger body habitus for age and sex. All three equations yielded lower P30 values in underweight compared to non-underweight subjects.


U25 eGFR slightly overestimated mGFR in underweight compared to non-underweight subjects, with U25 eGFR(cr) exhibiting the smallest bias of the three equations in this BMI group. The U25 equations performed well in non-underweight children, adolescents and young adults with CKD.

 BMI Category
N subjects (observations)44 (65)204 (485)87 (138)63 (144)
Mean Bias (eGFR-mGFR), mL/min/1.73m2, Est. (95%CI)    
U25 eGFR(cr)1.7
(-0.7, 4)
(-1.2, 1.2)
(-3.8, -0.2)
(-0.4, 4.6)
U25 eGFR(cysC)4.6
(1.8, 7.5)
(-1.8, 0.2)
(-3.8, -0.2)
(-3.8, 0.5)
U25 eGFR(avg)3.1
(0.9, 5.2)
(-1.2, 0.6)
(-3.5, -0.4)
(-1.7, 1.9)
P30: % eGFR within 30% of mGFR    
U25 eGFR(cr)79%88%91%81%
U25 eGFR(cysC)75%88%90%84%
U25 eGFR(avg)80%92%95%90%

1. Calculated from intercept only mixed effects model of eGFR-mGFR with subject-specific random intercept.


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