Diuretic renogram clearance half-times in the diagnosis of obstructive uropathy: effect of age and previous surgery.

ABSTRACT

Diuretic renography with radiotracers has been used successfully to diagnose obstruction in patients with hydronephrosis. Controversy persists with regard to the best approach for the interpretation of renogram curves visual analysis or a quantitative index, i.e. the clearance half-time. The latter is often reported to be in the intermediate or non-diagnostic range. It is important to measure the incidence of equivocal half-times in various subsets of patients with hydronephrosis in order to determine in which settings the measurement of this index may be clinically useful. We performed a retrospective study of diuretic renograms performed at our institution between 1997 and 2000 for the evaluation of suspected uretero-pelvic junction (UPJ) obstruction. Vigorous intravenous hydration, exceeding current guidelines, was employed in these patients. Three hundred and seventy-seven renogram curves in 205 patients were analysed. Patients were divided into three groups >1 year of age; who had previously undergone surgical correction of obstruction regardless of age. Patients with reflux or anatomical abnormalities of the urinary tract, those with chronic renal failure, those with bilateral normal clearances before furosemide administration and those with unilateral normal clearances before furosemide administration with contralateral poor renal function were excluded. In the remaining 119 patients, 205 clearance half-times were classified as normal before furosemide, normal after furosemide (half-time, <10 min), prolonged (half-time, >20 min) or intermediate (half-time, 10-20 min). In patients >1 year of age, 37% of 101 renograms showed normal half-times before furosemide, 20% showed normal half-times after furosemide, 44% showed prolonged half-times and none (0%) showed an intermediate half-time. In patients furosemide, 16% showing normal clearance after furosemide, 19% showing abnormal half-times and 17% showing intermediate half-times. In 33 renograms from patients who had undergone corrective surgery, 49% had normal half-times, 24% had prolonged half-times and 27% had intermediate half-times. It can be concluded that, when using the selection criteria, hydration, acquisition and processing protocols and half-time definition employed in this study, the addition of a clearance measurement in patients older than 1 year with suspected UPJ disease enhances patient classification and may improve the diagnostic confidence. There was a significantly higher incidence of intermediate half-times in patients with native disease aged <1 year than in those >1 year. Caution is advised when interpreting this finding in this age group. The measurement of washout was less useful in patients who had undergone a corrective procedure, because of the high rate of 'indeterminate' and 'abnormal' values in spite of successful surgery. Vigorous intravenous hydration, exceeding current standards, may have contributed to the lower incidence of intermediate half-times than reported previously.