To evaluate whether the bladder size on the voiding cystourethrogram (VCUG) might be a proxy for voiding abnormalities. Voiding abnormalities have been implicated in the development of hydronephrosis, reflux, and urinary tract infections.

We evaluated the volume of contrast infused for 617 consecutive VCUGs. We compared the actual volume infused during the VCUG to the expected bladder capacity. We correlated the percentage of predicted capacity with (a) the reason for the VCUG; (b) the VCUG results; (c) the patient's sex; and (d) their body mass index. We analyzed the results for the entire group, as well as by age, sex, reflux grade, and body mass index. We also examined the findings from those patients undergoing consecutive studies.

The bladder size on the VCUG was greater than predicted (1.74 times predicted). This was particularly true for patients <2 years old (2.22 vs 1.41 times predicted; P < .001) and for boys (2.01 vs 1.63 times predicted; P < .001). Both the reason for the VCUG (more prenatal patients with hydronephrosis than others; P < .001) and the VCUG findings (new reflux found more than others) had a relationship with the bladder size on the VCUG (P < .001). The body mass index did not correlate with the bladder size on the VCUG. Of the 87 patients undergoing 2 studies, the 53 patients with either no or improved reflux on the second study tended to have a larger than predicted bladder size on the VCUG (P = .07).

The bladder volume on the VCUG was greater than predicted for male infants with prenatal hydronephrosis and reflux. In other groups, the marked variation within groups prevented the use of the bladder volume on the VCUG as a proxy for voiding dysfunction.