Your doctor may ask for an Ultrasound examination of Kidney Ureter & Bladder region. This is a good screening tool for many Urinary tract problems ranging from Infection to stones and even Tumors.
Ureteric stones are not well visualized sometimes due to gas in Intestines.
You will be asked to drink some water to make urine bladder full for examination.
You do not need to be empty stomach for KUB Ultrasound.