Clinical determinants of discordance between estimated glomerular filtration rates based on serum creatinine vs cystatin C in critically ill patients

Purpose Accurate assessment of kidney function is critical for safe medication dosing in critically ill patients. However, discordance between serum creatinine–based estimated glomerular filtration rate (eGFRcr) and cystatin C–based eGFR (eGFRcys) is frequently observed in the intensive care unit (ICU), potentially complicating the interpretation of kidney function and leading to suboptimal clinical decisions. This study aimed to identify clinical determinants associated with discordance between eGFRcr and eGFRcys in critically ill patients. Methods We performed a retrospective analysis of 325 adult patients with both serum creatinine and cystatin C measurements obtained between April 2020 and October 2025. eGFR discordance was defined as an eGFRcys value more than 30% lower than the eGFRcr value. Multivariate logistic regression was used to identify clinical determinants associated with eGFR discordance. ICU mortality and the development of acute kidney injury (AKI) were also evaluated. Results eGFR discordance was observed in 171 patients (53%). Factors independently associated with eGFR discordance included older age (adjusted odds ratio [aOR], 1.04; 95% confidence interval [CI], 1.02-1.06), 12 or more days from ICU admission to initial blood sampling (aOR, 4.29; 95% CI, 2.20-8.33), hypoalbuminemia (aOR, 2.53; 95% CI, 1.51-4.37), and corticosteroid use (aOR, 2.19; 95% CI, 1.15-4.17). ICU mortality did not differ significantly between groups, whereas AKI occurred more frequently in patients with eGFR discordance (P = 0.046). Conclusion Discordance between eGFRcr and eGFRcys is common in critically ill patients. Older age, corticosteroid use, hypoalbuminemia, and delayed blood sampling increase the likelihood of substantial eGFR discordance. Recognizing these factors may help clinicians refine kidney function interpretation and optimize the dosing of renally eliminated drugs in ICU settings.