Question: My urologist would like me to bill for an ultrasound on the bladder to check volume, but I am not sure which ultrasound code to use for this. This was done in a clinical setting. Which code is best? Massachusetts Subscriber Answer: Submit 51798 (Measurement of post-voiding residual urine and/or bladder capacity by ultrasound, non-imaging) for this service. If your urologist does the bladder sonogram primarily to determine the postvoid residual urine (PVR), use 51798 no matter what equipment the urologist uses and whether or not he derives an image from the equipment. Most urologists, however, do a bladder sonogram primarily for PVR determination and this should be billed with 51798. Exception: If the urologist uses the sonogram primarily to view the anatomy or architecture of the bladder, and the PVR is only part of – but not the main reason for – the study, bill 76857 (Ultrasound, pelvic [nonobstetric], real time with image documentation; limited or follow-up [e.g., for follicles]) instead. This is usually the only circumstance in which you should bill 76857.