Measuring Renal Function In Critically Ill Patients-True GFR Versus Urinary Creatinine Clearance And Estimating Equations

Objective:To evaluate the agreement of urinary creatinine clearance (CrCl) and estimating equations, in comparison to GFR measured (mGFR) by the infusion clearance of iohexol, in critically ill patients.Methods:49 patients were studied in the intensive care unit of Peking Union Medical College Hospital. We investigated the correlation, agreement between mGFR (iohexol clearance) and urinary creatinine clearance (CrCl), five estimating equations (eGFR).1-, 4-,12- and 24-houred urine was collected, Glomerular filtration rate was estimated by the Cockcroft Gault (CG), the Modification of Diet in Renal Disease (MDRD), the Simplified MDRD, the Chinese MDRD and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. We also evaluated the diagnostic value of Serum Creatinine (SCr) and CystatineC (CysC).Result:The correlations of CrCl (1 h,4 h,12 h,24 h-CrCl) and eGFR (CG, MDRD, sMDRD, cMDRD, CKD-EPI)were moderate, with r values ranging from 0.735 to 0.930. Agreement between CrCl, eGFR and mGFR was very low for all urine collections and five equations, with ICC< 0.8, wide 95% LoA in Bland-Altman analysis (minimum o: [-13.2-36.6]). CysC had a strong correlation (rs=-0.915, p< 0.001)with iGFR, better than SCr (rs=0.734, p< 0.001).Conclusion:The study demonstrated poor precision of the commonly utilized urinary CrCl and equation method for assessment of GFR in critically ill patients. CysC significantly outperforms SCr for the detection of GFR.