Patients with renal cysts do not need to fast in principle if they want to have a kidney ultrasound, because this is determined by the location of the kidneys. The kidneys are located on both sides of the retroperitoneal spine, one on the left and one on the right, and there is no intestinal cavity blocking the front and back of the kidneys, so the intestinal peristalsis caused by eating does not have much effect on the observation of the kidneys under ultrasound. It is important to note that doing kidney ultrasound on an empty stomach is more conducive to observing the structure and size of the kidney, as well as the number and size of cysts in the kidney.