Creatinine Clearance and Estimated Glomerular Filtration Rate – When are they Interchangeable
Study goal was to examine which of glomerular rate equations is most suitable for prediction of creatinine clearance. Using a retrospective review of data from 500 hospital patients we calculated glomerular filtration rate according to Cockcroft-Gault equation (C-G), Modification of Diet in Renal Disease Study equation (MDRD) and Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI). We determined if results of these equations were compatible with creatinine clearance, and does stage of kidney disease, body-mass index (BMI), diabetes or old age have an impact on their ability to predict creatinine clearance. All of the equations showed high correlations with creatinine clearance, regardless of diabetes, overweight or old age. There was no statistical difference (p<0.05) between diagnostic accuracy when comparing ROC plots for MDRD and CKD-EPI at creatinine clearance cut offs of 60 ml/min/1.73 m2 and 90 ml/min/1.73 m2 when analyzingdata for all subjects, older subjects (>65 years) and diabetics. The percentage of overweight subjects (BMI>25) in false positives (subjects with normal creatinine clearance and decreased GFR) was 64.8% for C-G, 88.6% for MDRD and 88.9% for CKD-EPI. Large number of overweight subjects with normal creatinine clearance and decreased GFR would indicate that creatinine clearance overestimates GFR in overweight subjects. Passing-Bablok regression showed agreement between creatinine clearance and MDRD and creatinine clearance and CKD-EPI only in cases of severely decreased GFR (G4 and G5 stage of chronic kidney disease). Only in these stages of chronic kidney disease can creatinine clearance and MDRD or creatinine clearance and CKD-EPI be used simultaneously.
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