The Performance of Equations That Estimate Glomerular Filtration Rate against Measured Urinary Creatinine Clearance in Critically Ill Patients.

The performance of glomerular filtration rate- (GFR-) estimating equations was studied against creatinine clearance measured by 24-hour urine collection (CrCl) in critically ill patients. . In this substudy of the PermiT trial (https://clinicaltrials.gov/ct2/show/ISRCTN68144998), patients from King Abdulaziz Medical City-Riyadh who had CrCl were included. We estimated GFR using Cockroft-Gault (CG), modification of diet in renal disease study (MDRD), chronic kidney disease epidemiology collaboration (CKD-EPI), and Jelliffe equations. For the CG equation, we entered the actual weight in one calculation (CG), and if BMI ≥30 kg/m, we entered the ideal body weight (CG) and the adjusted body weight (CG) in two calculations. We calculated the MDRD equation based on 4 (MDRD-4) and 6 variables (MDRD-6). The performance of these equations was assessed by different ways including Spearman correlation, bias (difference between estimated GFR and CrCl), precision (standard deviation of bias), and Bland-Altman plot analysis. . The cohort consisted of 237 patients (age 45 ± 20 years, males 75%, mechanically ventilated 99% with serum creatinine 101 ± 94 mol/L and CrCl 108 ± 69 ml/min/1.73 m). The correlations between the different equations and CrCl were modest (: 0.62 to 0.79; < 0.0001). Bias was statistically significant for CG (21 ml/min), CG (12 ml/min), and MDRD-6 (-10 ml/min) equations. Precision ranged from 46 to 54 ml/min. The sensitivity of equations to correctly classify CrCl 30-59.9 ml/min/1.73 m was 17.2% for CG, 30.0% for CG, 31.0% for CG, 31.0% for MDRD-4, 39.1% for MDRD-6, 13.8% for CKD-EPI, and 34.5% for Jelliffe equation. . Commonly used GFR-estimating equations had limited ability to properly estimate CrCl and to correctly classify GFR into clinically relevant ranges that usually determine dosing of medications.