Reproducibility of technetium-99m ethylenedicysteine clearance

It has been shown that technetium-99m ethylenedicysteine (Tc-99m-EC) cleara nce displays a strong correlation with orthoiodohippurate clearance and tha t it is possible to estimate effective renal plasma flow from Tc-99m-EC cle arance. However, in routine practice, when monitoring renal function of pat ients by clearance determinations it is imperative to test the reproducibil ity of the clearance technique in order to decide whether the changes in re nal function are related to disease or not. The aim of this study was to re st the reproducibility of Tc-99m-EC clearance. The study group comprised 13 patients aged between 24 and 58 years (eight female and five male). Two pa tients had single kidneys due to agenesis and hypoplasia. Plasma creatinine and BUN levels were within the normal range and remained stable between tw o clearance studies. None of the patients were receiving medication. Two Se parate multiple sample clearance studies were performed in each patient wit hin a week. The difference between two studies was expressed as a percentag e of the mean value of the two studies, and the standard deviation of these percentages represented the precision. The plasma clearance of Tc-99m-EC i n the first-step studies ranged from 190 ml/min to 561 ml/min with a mean o f 411+/-101 ml/min. The clearances obtained from the second-step studies ra nged from 248 ml/min to 552 ml/min, with a mean of 387+/-94 ml/min. There w as no statistically significant difference between the two clearance studie s (P>0.05). There was a mean difference of 5.3% between the first and secon d clearance studies, and the precision was found to be 12.7%. In conclusion , this study suggested that consecutive Tc-99m-EC clearance measurements sh ould be interpreted cautiously.