Accuracy of ultrasonic assessment of residual urine in children.

Bladder volumes were determined by realtime ultrasonography and compared to catheterised volumes in a consecutive series of 101 children. Volumes were calculated as the product of the longitudinal, transversal and sagittal diameter and a correction factor of 0.52. There was a good correlation between the methods (r = 0.96) although large volumes tended to be underestimated by ultrasonography. Small volumes could be assessed accurately.