Measurement of glomerular filtration rate in adults: accuracy of five single-sample plasma clearance methods

After an intravenous injection of a tracer that is removed from the body solely by filtration in the kidneys, the glomerular filtration rate (GFR) can be determined from its plasma clearance. The method requires a great number of blood samples but collection of urine is not needed. In the present investigation the total plasma clearance of 51Cr-EDTA (ethylenediaminetetra-acetate) was assessed from 13 blood samples taken 5-300 min post-injection in 44 adult patients with GFR greater than 15 ml min-1. In 34 of these patients the plasma clearance of 99Tcm-DTPA (diethylenetriaminepenta-acetate) was determined simultaneously. Using these clearance values as reference the accuracy of six simplified methods were studied: five single-sample methods and one five-sample method. The standard error of estimate (SEE) of the single-sample methods ranged from 4.2 to 7.5 ml min-1 using EDTA, and from 3.8 to 6.3 ml min-1 using DTPA. SEE of the five-samples method was 3.0 ml min-1 (EDTA) and 3.1 ml min-1 (DTPA). The single-sample methods given by Christensen & Groth (1986) and by Tauxe (1986) are recommended for daily use, as SEE was small even at low GFR values. In patients with GFR less than 80 ml min-1, in whom a highly accurate determination is needed, a multiple samples method is recommended, e.g., Brøchner-Mortensen (1972).