[Measuring residual urine by portable ultrasound scanner]

Urethral catheterization, the standard method of measuring residual urine, is uncomfortable and associated with risk of infection and trauma to the urethra. It has also been reported as inaccurate to a certain extent. We compared catheterization with ultrasound scanning in a prospective study of 52 men and 3 women. 100 measurements of postvoiding residual urine by portable ultrasound scanner, were each followed immediately by urethral catheterization (both procedures performed by an experienced nurse in our outpatient clinic). A difference of > 25 ml between measurements by scanner and by catheter was considered significant. The range of residual urine measured by scanner was 1-425 ml, and by catheter 1-410 ml. There was good matching between the 2 methods in 85 of 100 measurements (scanning accuracy 85%). In 30/85 matching was excellent while in 55 cases the mean difference was 8.5 +/- 6.2 ml, range 1-24 ml. The accuracy of scanning was 85%; there was perfect matching between the 2 methods in 30 cases. In the remaining 15 cases the mean difference was 41.8 +/- 13.6 ml (range 25-56). Each catheterization took 4-5 minutes and scanning 30 seconds. There were no complications after catheterization, but all reported discomfort and dysuria for 1-2 hours thereafter. Scanning was absolutely uneventful in all. The cost per catheterization, including medication, disposable materials and personnel time was approximately 80 NIS. Our 80-90 measurements of residual urine a month require annually about 80 hours and a budget of about NIS 80,000. Scanning requires only 8 hours, while the cost of the portable scanner is significantly less than NIS 80,000 and it can be used for more than a year. We conclude that measuring urine residual with the noninvasive scanner instead of by catheterization is easier, more accurate, and more cost-effective.