DETERMINATION OF THE GLOMERULAR-FILTRATION RATE BY IDENTIFICATION OF SINISTRIN KINETICS

A computer-based method of system identification and estimation of par ameter variance for two-compartment models matched to dynamic sinistri n concentration profiles for the determination of glomerular filtratio n rate is described. Thereby a procedure for the judgment of the optim al sampling time horizon is presented. Since single-injection techniqu es are suspected of yielding systematic overestimation of the glomerul ar filtration rate, a method is demonstrated confirming that such a te chnique employing sinistrin kinetics can be used to correctly determin e the glomerular filtration rate. The validation of the system paramet ers gained by the single-injection method is made through prediction o f the concentration contour under a constant infusion regimen in the s ame subject on a different occasion. This was performed in healthy con trols and in patients with various degrees of renal insufficiency. Upo n consideration of the dependence of the clearance estimates and their variances on the protocol duration in test subjects examined from fou r to ten hours, an adaptive design of the protocol length is developed .