PurposeTo determine how a formula to estimate kinetically changing glomerular filtration rate (keGFR) relates to serum creatinine changes and to compare the discriminatory ability of keGFR to that of perioperative change in serum creatinine to predict acute kidney injury (AKI) and mortality. Materials and MethodsRetrospective cohort study at a single-tertiary-care Midwestern university hospital of 4022 patients admitted to the intensive care unit between January 2006 and January 2012 immediately after cardiac surgery. Measurements and Main ResultsOf 4022 patients, 1031 (25.6%) developed at least AKI stage 1 and 1106 (27.5%) developed AKI-min. Patients who developed AKI stage 1 or AKI-min had a greater decrease in keGFR, both by absolute amounts and by percentage. After adjusting for other factors with logistic regression, keGFR had good discrimination (c statistic = 0.787 and 0.749, respectively) in predicting AKI and operative mortality. ConclusionDespite no change in immediate perioperative serum creatinine levels, keGFR fell and this predicted subsequent AKI. Using keGFR enables identification of patients who, despite unchanged postoperative creatinine, incur clinically significant kidney injury based on reduction in GFR and increased mortality.