Estimation of GFR in Patients With Cystic Fibrosis: A Cross-Sectional Study

Abstract

Background: Patients with cystic fibrosis (CF) have frequent infectious complications requiring nephrotoxic medications, necessitating monitoring of renal function. Although adult studies have suggested that cystatin C (CysC)-based estimated glomerular filtration rate (eGFR) may be preferable due to reduced muscle mass of patients with CF, pediatric patients remain understudied. Objective: Our objective was to determine which eGFR formula is best for estimating glomerular filtration rate (GFR) in pediatric patients with CF. Methods: A total of 17 patients with CF treated with nephrotoxic antibiotics were recruited from the Children’s Hospital at London Health Sciences Centre, London, Ontario, Canada. 99Tc DTPA GFR (measured GFR [mGFR]) was measured with 4-point measurements starting at 120 minutes using a 2-compartmental model with Brøchner-Mortensen correction, with simultaneous measurement of creatinine, urea, and CysC. The eGFR was calculated using 16 known equations based on creatinine, urea, CysC, or combinations of these. Primary outcome measures were correlation with mGFR, and agreement within 10% for various eGFR equations. Results: Mean mGFR was 136 ± 21 mL/min/1.73 m2. Mean creatinine, CysC, and urea were 38 ± 10 μmol/L, 0.72 ± 0.08 mg/L, and 3.9 ± 1.4 mmol/L, respectively. The 2014 Grubb CysC eGFR had the best correlation coefficient ( r = 0.75, P = .0004); however, only 35% were within 10%. The new Schwartz formula with creatinine and urea had the best agreement within 10%, but a relatively low correlation coefficient ( r = 0.63, P = .0065, 64% within 10%). Conclusions: Our study suggests that none of the eGFR formulae work well in this small cohort of pediatric patients with CF with preserved body composition, possibly due to inflammation causing false elevations of CysC. Based on the small numbers, we cannot conclude which eGFR formula is best.

Longitudinal assessment of renal function after lung transplantation for cystic fibrosis: transition from post-operative acute kidney injury to acute kidney disease and chronic kidney failure

“…First, to assess the incidence of CKD we utilized the most recent iteration of the CKD-EPI calculation of GFR based on sCr [14], which in a population of patients suffering from depleted muscle mass might be particularly biased. In this cohort of patients, cystatin-C clearance-based calculation of GFR has proven more accurate [30], and thus future studies should base their analysis on equations obtained using cystatin-C clearance. Second, this is a study from a highly specialized unit including only patients with cystic fibrosis, thus limiting the generalizability of our results to the broader patient population.…”

Biochemical Aspects of Cystic Fibrosis and Kidney Disease: A Brief Discussion

“…Cystatin C (Lamb, 2015) is a novel protein used to evaluate renal function within the last decade; serum concentration is largely determined by glomerular filtration, making it an endogenous marker helpful for the assessment before metabolism by a proximal tubule. On the other hand, the results of the small number of studies in CF have not been fully evaluated (Wallace et al, 2020) and the superiority of this measure (Sorkhi et al, 2018) has been indicated, but 47 adult and pediature patients have found no statistical benefits in their studies over any alternative method of estimation of renal function and more sufficiently powdered.…”

Discrimination of Chronic Kidney Disease and Diabetic Nephropathy and Analysis of Their Related Influencing Factors

“…24 The level of cysteine protease inhibitor C (Cys-C) is determined by glomerular filtration, not affected by any external factors (gender, age, diet). 25 Slightly elevated of Cys-C level may indicate renal insufficiency, but its low level can also happen in early kidney damage. [26][27][28]…”