Comparison of creatinine and cystatin C estimation of glomerular filtration rate in the Fontan circulation

Abstract

BackgroundThe Fontan circulation is associated with low skeletal muscle mass, which affects the accuracy of creatinine-based glomerular filtration rate estimates (eGFR/GFR). Cystatin C, another filtration marker, is less impacted by muscle mass. We examined associations between characteristics of individuals with a Fontan circulation and both creatinine-based and cystatin C-based eGFR. Methods and resultsThis single-center retrospective study included 107 individuals with a Fontan circulation who had clinical measurements of serum cystatin C and creatinine. GFR was estimated using different equations for adults (≥19 years of age, Chronic Kidney Disease-Epidemiology Collaboration equations for both creatinine and cystatin C) and children (<19 years of age, Schwartz and Larsson equations, for creatinine and cystatin C, respectively). Chronic kidney disease (CKD) was defined as an eGFR <90 ​mL/min/1.73 ​m2.Mean eGFR was 115.2 ​± ​23.9 by creatinine, and 113.6 ​± ​22.7 ​mL/min/1.73 ​m2 by cystatin C. CKD was identified in 16 individuals. Those with CKD as defined by cystatin C had a lower median platelet count (163 [115, 194] vs. 191 [153, 252] p ​= ​0.048), had lower saturations (87.5% [85.3%, 94%] vs. 94% [91%, 95%], p ​= ​0.006) and were more likely to have at least moderate atrioventricular valve regurgitation (31% vs. 7%, p ​= ​0.01). While the same number of patients were classified as having CKD using creatinine-based equations, creatinine-based CKD was only associated with lower saturations (92% [85.3%, 93.8%] vs. 94% [91%, 95%], p ​= ​0.02). ConclusionsAmong individuals with a Fontan circulation, defining CKD based on cystatin C rather than creatinine appears to identify a group of patients with characteristics associated with increased risk for clinical deterioration.