A general equation for estimating glomerular filtration rate from a single plasma sample

Abstract

There were significant differences between GFR values obtained using the international guidelines single-sample method and the slope-intercept method described in the BNMS guidelines. The new equation described in this paper gave considerably improved agreement and is recommended if single-sample estimates are to be used as quality control for BNMS guideline measurements.

Quality control of slope–intercept measurements of glomerular filtration rate using single-sample estimates

“…± 3 standard deviations) as defining the level at which the user should be alerted to a potential problem. It is clear from previous studies [9,10] that the differences between one-sample and slope-intercept GFR values vary with GFR. It was assumed that square error (E) varied with GFR as a quadratic function and therefore equations of the following form were derived:…”

“…As errors were also known to depend on time of the sample and body surface area [9], more accurate error estimates were made by calculating values of J, K and L separately for adults at 120, 180 and 240 min and for children at 120 and 180 min. For intermediate times (t), the expected square error could be estimated by linear interpolation of the coefficients.…”

“…Single-sample estimation Separate estimates of body surface area corrected GFR (GFR BSA ) for both samples for each subject were calculated using the new single sample equation derived specifically for consistency with GFR calculated using the BNMS guidelines technique [9]:…”

“…This information is then developed to form a quality control scheme where samples falling outside the expected error limits can be identified. Single-sample equations derived specifically for the BNMS Guidelines technique for GFR measurement are used in this study [9].…”

Ontogeny of drug elimination by the human kidney

“…Plasma clearance of 51 Cr-EDTA (chromium-labeled ethylenediaminetetraacetic acid) or 99m Tc-DTPA (technetium-labeled diethylenetriamine penta-acetate) has become widely accepted as a standard measure of renal function [11]. In addition, many mathematical equations and nomograms have been proposed in order to predict [15] creatinine clearance on the basis of readily available patient characteristics such as weight, age, and plasma creatinine level (PCr) [12].…”