[On the diagnostic value of semi-quantitative kidney function tests. I. Correlation of plasma concentration of "genuine" endogenous creatinine and inulin clearance]

Determination of the glomerular filtration rate by identification of sinistrin kinetics

A computer-based method of system identification and estimation of parameter variance for two-compartment models matched to dynamic sinistrin concentration profiles for the determination of glomerular filtration rate is described. Thereby a procedure for the judgment of the optimal sampling time horizon is presented. Since single-injection techniques are suspected of yielding systematic overestimation of the glomerular filtration rate, a method is demonstrated confirming that such a technique employing sinistrin kinetics can be used to correctly determine the glomerular filtration rate. The validation of the system parameters gained by the single-injection method is made through prediction of the concentration contour under a constant infusion regimen in the same subject on a different occasion. This was performed in healthy controls and in patients with various degrees of renal insufficiency. Upon consideration of the dependence of the clearance estimates and their variances on the protocol duration in test subjects examined from four to ten hours, an adaptive design of the protocol length is developed.

Adaptation of a single injection clearance method to physiological and pathophysiological facts. A review of data obtained in infancy and childhood

A retrospective analysis of 395 51Chromiumethylenediaminotetraacetate single injection clearances performed in infants and children is presented. In 61% of infants and 30% of the children the clearance values were calculated on the basis of a plasma disappearance half time of the reference substance, which was longer than the standard study, i.e. on the basis of extrapolated data. Plasma creatinine and urea levels were found to be appropriate indicators for predicting the plasma disappearance half time of the marker substance. 14 additional patients were studied prospectively with a duration of the study predicted by means of the plasma creatinine and urea levels. In these patients, separate determinations of the clearances using either the data obtained during the standard time of procedure only, or the data of the entire study, clearly demonstrated that the clearances obtained by means of the standard procedure overestimated glomerular filtration rate. The analysis of the data in infants show that the plasma urea level is a reasonably good indicator for predicting the time schedule of the study whereas plasma creatinine should not be used. Additionally the retrospective data indicate that a prolongation of the study should be recommended in all infants. This study demonstrates the necessity and offers means of adapting the time schedule of isotope single injection clearances to physiological and pathophysiological facts.