Calculation of the renal clearance by dynamic measurement of the excreted activity

Aim: In this paper we present a new method to measure the renal slope-clear ance of Tc-99m-MAG-3 in a single-shot model (Excretion-clearance). Method: A renal scintigraphy with Tc-99m-MAG-3 was performed in 22 patients. The ex creted activity of the tracer in the kidneys and the bladder was dynamicall y measured using a double-head gamma-camera. Additionally the total absorpt ion over the kidneys and the bladder was determined. The Excretion-clearanc e was calculated in a differential and an integral variant. Simultaneously the 2-compartment-clearance (Sapirstein-clearance), the Oberhausen-clearanc e and the Bubeck-clearance were calculated. Results: The Sapirstein-clearan ce is considered as the "goldstandard" in a single-shot modell. The correla tion of the Bubeck-clearance and the Oberhausen-clearance ranged from r = 0 .96 to r = 0.97, the Excretion-clearance (diferential-method) correlated wi th r = 0.90. The absolute difference of the clearance-values was lowest com paring the Bubeck-clearance with the Sapirstein-clearance with an average d ifference of 11%, whereas the Excretion-clearance revealed at least an aver age difference of 21% and the Oberhausen-clearance of 24%. Discussion: The Excretion-clearance requires a more complicated protocoll measuring the cle arance in comparison to the Bubeck-clearance. The results of the excretion- clearance differ more from the Sapirstein-clearance with regard to the exam ined patient population than the Bubeck-clearance. Regarding the theoretica l basis of the methods, we expect advantages of the Excretion-clearance com pared with the Bubeck-Clearance in patients with compartmental disproportio n or with a low clearance, We are going to prove this in combination with t he above mentioned methodical improvements in a further study.