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.