Background and Aims An increasing number of asymptomatic newborns are investigated for antenatally detected hydronephrosis (ADH). Postnatal tests include ultrasound scan (USS), micturating cystourethrogram (MCUG) and radionuclide scan, usually mercaptoacetyltriglycine (MAG3). Output efficiency (OE) on MAG3 scan has been suggested to improve diagnostic accuracy of diuretic renography and we studied the usefulness of this additional parameter in ADH patients.

Methods Infants who on initial postnatal USS had a renal pelvic diameter (RPD) >10 mm underwent same day detailed USS and MAG3 scan at approximately 3 months of age.

Results 28 patients (20 male) had same day USS and MAG3 scans. Mean age at follow up was 37 months. 35 kidney units were studied in 28 patients (seven had bilateral involvement). 29 kidney units in 22 patients with ADH were managed conservatively (CM) and 6 patients underwent pyeloplasty (P) at a mean age of 10.6 months (range 5–17 months). The decision to perform pyeloplasty was made after discussion at nephrouro-radiology meeting where RPD, cortical thickness on USS were combined with OE, response to frusemide and residual activity on a delayed image. Mean OE of the P group was 50.6% (range 42–60%; normal >78%) compared to 70.5% (range 44–99%) in the CM group. 18 of the 29 units (62%) of the CM group had OE <78%. OE values alone did not appear to influence decision-making. Mean RPD and cortical thickness (average of upper and lower poles) was 27.1 mm and 3.9 mm, respectively, in the P group compared to 18.4 and 8.0 in the CM group. Vesicoureteric reflux was detected on MCUG in 11 (20%) of 54 kidney units (one patient did not have MCUG) but was grade 2 or less in all cases and in four cases was the side opposite to RPD.

Conclusion In young infants OE alone on MAG3 scan does not assist when selecting patients with ADH for pyeloplasty which needs to be based upon consideration of all USS and MAG3 scan parameters. The authors suggest that MCUG should not be a routine investigation in these infants.