Reliability of serum creatinine-based formulae estimating renal function in non-critically ill surgery patients: Focus on augmented renal clearance

What is known and objectivesFormulae estimating glomerular filtration rate (GFR) are frequently used to guide drug dosing. The objectives of this prospective single-center study were to evaluate agreement between these equations and measured creatinine clearance (CrCl) in non-critically ill surgery patients with normal kidney function and augmented renal clearance (ARC, CrCl130mL/min/1.73m(2)), to determine predictors for disagreement, define a GFR estimator cut-off value identifying ARC and determine the ARC prevalence and duration in non-critically ill surgical patients. MethodsHospitalized adult non-critically ill abdominal and trauma surgery patients were eligible for inclusion. Measured CrCl based on an 8-hour urinary collection (CrCl8h) was used as the primary method for determining kidney function. Agreement between equations and measured CrCl8h was assessed in terms of precision, defined as a bias within 10mL/min/1.73m(2). Predictors for disagreement were identified for the most precise estimator using an ordinal logistic regression model with negative bias, agreement and positive bias as outcome variables. A receiver operating characteristic (ROC) analysis was performed to identify an estimator cut-off predicting ARC, which was subsequently applied for the daily proportion of patients displaying ARC and ARC duration. Results and discussionDuring the study period (14/11/2013 - 13/05/2014), in 232 adult non-critically ill abdominal and trauma surgery patients, all estimators tend to underestimate CrCl8h (mean bias ranging from 17 to 22mL/min/1.73m(2)), especially in patients displaying ARC (mean bias ranging from 44 to 56mL/min/1.73m(2)). eGFR(CKD-EPI) performed the best. Younger age and low ASA score independently predicted underestimation of CrCl8h. Three different eGFR(CKD-EPI) cut-offs with decreasing sensitivity and increasing specificity (84, 95 and 112mL/min/1.73m(2)) identified, respectively, 65%, 44% and 14% patients displaying ARC. The median ARC duration was 4, 4 and 3days, respectively. What is new and conclusionIn surgical patients, eGFR frequently underestimates measured CrCl, especially in young patients with low ASA score. eGFR cut-offs predicting ARC were identified.