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

Summary. 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>15 ml min^-1. In 34 of these patients the plasma clearance of ⁹⁹Tc^m-DTPA (diethylenetri-aminepenta-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 < 80 ml min^-1, in whom a highly accurate determination is needed, a multiple samples method is recommended, e.g., Brøchner-Mortensen (1972).