Clinical agreement between automated and calculated ultrasound measurements of bladder volume

Non-invasive urine volume measurement is an important tool in the management of dysfunctional and neuropathic bladders in children. Ultrasound imaging devices have been used for many years for this purpose. An automated scanner (Bladderscan) is now available and has been recommended by a number of authors, but there is conflicting evidence in the literature regarding the accuracy and appropriate clinical application of the device. We aimed to assess the level of clinical agreement between the two methods. 36 urine volume measurements were made on 11 children using both instruments. Although there was a good correlation between the methods (r=0.97), the clinical agreement was poor (limits of agreement +/- 77 ml). 13 voided volumes were directly measured and compared with the difference between pre- and post-void ultrasound measurements. The systematic errors were small but the mean absolute errors were 54 ml and 23 ml, respectively, for the automated and ultrasound imaging methods. If used correctly, ultrasound imaging provides more accurate results and can compete with the cost, convenience and ease of use of the automated method. Low cost, highly portable ultrasound imaging devices are now available and should be used in preference to the Bladderscan.