Impact of Recent Acute Kidney Injury on Creatinine Clearance Estimation in Critically Ill Patients Undergoing Cardiac Surgery

Acute kidney injury (AKI), often present in critically ill patients and patients with cardiac dysfunction, may alter estimates of renal function. The impact of recent AKI on the accuracy of the Cockcroft-Gault creatinine clearance equation (CG-CrCl) before cardiac surgery is unknown. This single-center, retrospective study included patients who underwent cardiac surgery from 1 January 2006 through 30 June 2012 and whose 24-hour urine creatinine clearance (24hr-CrCl) was measured in the intensive care unit before surgery. We evaluated CG-CrCl accuracy by calculating absolute differences between 24hr-CrCl and CG-CrCl estimates. Clinical impact was signified by discrepancies in United States Food and Drug Administration (FDA) renal impairment stage indicated by 24hr-CrCl versus CG-CrCl estimates. Acute kidney injury was evaluated by using Kidney Disease: Improving Global Outcomes criteria. Of 161 patients, 93 (58%) had recent AKI: stage 1, 31 (33%); stage 2, 39 (42%); and stage 3, 23 (25%). In mL/min, the CG- CrCl overestimated 24hr- CrCl (absolute difference: total, -10 +/- 25; no AKI, -7 +/- 26; stage 1, -8 +/- 17; stage 2, -16 +/- 28; and stage 3, -10 +/- 26; P=0.29). Renal impairment stages assigned by CG-CrCl did not match 24hr-CrCl in 70 (43%) of the 161 patients, especially those with recent AKI: no AKI, 24/68 (35%); stage 1, 13/31 (42%); stage 2, 23/39 (59%); and stage 3, 10/23 (43%). The CG-CrCl consistently overestimated 24hr-CrCl in critically ill patients before cardiac surgery. Clinicians should use the CG-CrCl cautiously when estimating renal function and medication dosages in this population.