Simplified algorithms for the estimation of 99Tcm-MAG3 clearance

The aim of this study was to evaluate two formulae allowing the determination of MAG3 clearance by means of a single blood sample, namely Bubeck's formula and Russell's formula. As a first step, a simulation study was performed with the two single-sample algorithms to predict MAG3 clearance as a function of plasma concentration, using various times for blood sampling and various body surface areas. As a second step, a validation study on 47 adult patients with varying renal function allowed a clinical comparison between the reference technique, namely the multiple blood sample technique, and the two simplified techniques. The simplified algorithms were calculated using the fitted value at 44 min. In the simulation study, whatever the time of blood sampling or the level of correction introduced for body surface area, the results obtained by means of Bubeck's algorithm diverged significantly from those of Russell's algorithm, for low clearance values as well as for high clearance values. The curve of the differences between the two methods had a typical boomerang shape. In the clinical study, the difference between Russell's algorithm and the reference method was generally within 20 ml.min-1, with no systematic bias; with Bubeck's algorithm there was a marked underestimation, both in the low and high clearance ranges. We suggest Russell's single-sample method is the method of choice.