Estimation of glomerular filtration rate in cancer patients

The frequent need to obtain an estimate of renal function in cancer patient s, not least for targeting carboplatin dose, has led to a number of approac hes to estimate glomerular filtration rate (GFR). This study aimed to devel op a simple and reliable method to estimate GFR using readily-available pat ient characteristics. Data from 62 patients with estimates of Cr-51-EDTA cl earance were analysed to determine the most appropriate formula relating th is method of measuring GFR to patient characteristics. The population pharm acokinetics of Cr-51-EDTA were analysed using NONMEM to evaluate the influe nce of each covariate. The formulae derived were then validated using a fur ther 38 patients and compared with those obtained using existing formulae. Cr-51-EDTA clearance (GFR) was positively related to Dubois surface area, n egatively related to age, and inversely related to serum creatinine (SCr). Females had lower Cr-51-EDTA clearance than males. The enzymatic method of SCr assay gave more reliable results than the Jaffe colorimetric method. A measure of creatine kinase significantly improved the estimation of GFR. Th e new formula produced estimates of GFR which were less biased (Mean Predic tion Error = -3%) and more precise (Mean Absolute Prediction Error = 12%) t han Cockcroft and Gault (-8% and 16%) or Jelliffe (-15% and 19%) estimates. The formulae developed here can be used to provide reliable estimates of G FR, particularly in regard to targeted dosing of carboplatin. (C) 2001 Canc er Research Campaign.