Opotowsky AR, et al. - Researchers examined the link between estimated glomerular filtration rate (eGFR), calculated using either the creatinine or cystatin C Chronic Kidney Disease–Epidemiology Collaboration equation, and both all-cause death and a composite outcome of mortality or nonelective cardiovascular hospitalization in adults with congenital heart disease (ACHD) (39 ± 14 years old, 49% female). Among 911 ACHD patients, clinical events were more strongly predicted by cystatin C-based eGFR vs creatinine-based eGFR. Specifically, there were doubts regarding creatinine-based methods in the Fontan circulation.