Radionuclide cystography: the significance of retention time of the refluxed radioisotope.

We studied 36 patients with vesicoureteral reflux into 45 renal units by means of isotope cystography and a dynamic renal function scan performed 24 to 48 hours after the cystography. Functional impairment was found in 21 renal units. To evaluate the significance of the time between voiding and complete disappearance of the radioisotope that refluxed from the kidney (retention time) the presence of the labeled particles in the kidney was followed continuously and intermittently during a prolonged interval. There was a significant difference between the retention time found in the impaired kidneys and that in the normally functioning kidneys. In 91.7 per cent of the normally functioning kidneys retention time was less than 5 minutes, whereas in 86 per cent of the impaired kidneys it was more than 10 minutes and in 56 per cent it was more than 20 minutes. No significant correlation was found between the retention time and intrarenal reflux or dilatation of the collecting system (patients classified as having radiological grades III and IV reflux were not included in this study). A retention time greater than 10 minutes may be correlated with decreased renal function. The retention of technetium sulfur colloid particles may be analogous to the retention of similar size bacteria and suggests a possible pathophysiologic explanation for the development of renal dysfunction owing to the prolonged presence of bacteria in the kidney after reflux.