Performance of the Chronic Kidney Disease-Epidemiology Study Equations for Estimating Glomerular Filtration Rate Before and After Nephrectomy

Purpose: Accurate renal function determination before and after nephrectomy is essential for proper prevention and management of chronic kidney disease due to nephron loss and ischemic injury. We compared the estimated glomerular filtration rate using several serum creatinine based formulas against the measured rate based on ¹²⁵I-iothalamate clearance to determine which most accurately reflects the rate in this setting. Materials and Methods: Of 7,611 patients treated at our institution since 1975 the measured glomerular filtration rate was selectively determined before and after nephrectomy in 268 and 157, respectively. Performance of the Cockcroft-Gault, Modification of Diet in Renal Disease Study, re-expressed Modification of Diet in Renal Disease Study and Chronic Kidney Disease-Epidemiology Study equations, each of which estimates the glomerular filtration rate, were determined using serum creatinine, age, gender, weight and body surface area. The performance of serum creatinine, reciprocal serum creatinine and the 4 formulas was compared with the measured rate using Pearson's correlation, Lin's concordance coefficient and residual plots. Results: Median serum creatinine was 1.4 mg/dl and the median measured glomerular filtration rate was 50 ml per minute per 1.73 m². The correlation between serum creatinine and the measured rate was poor (-0.66) compared with that of reciprocal serum creatinine (0.78) and the 4 equations (0.82 to 0.86). The Chronic Kidney Disease-Epidemiology Study equation performed with greatest precision and accuracy, and least bias of all equations. Stage 3 or greater chronic kidney disease (¹²⁵I-iothalamate glomerular filtration rate 60 ml per minute per 1.73 m² or less) was present in 44% of patients with normal serum creatinine (1.4 mg/dl or less) postoperatively. Such missed diagnoses of chronic kidney disease decreased 42% using the Chronic Kidney Disease-Epidemiology Study equation. Conclusions: Glomerular filtration rate estimation equations outperform serum creatinine and better identify patients with perinephrectomy compromised renal function. The newly developed, serum creatinine based, Chronic Kidney Disease-Epidemiology Study equation has sufficient accuracy to render direct glomerular filtration rate measurement unnecessary before and after nephrectomy for cause in most circumstances.