Generally speaking, the difference between catheterization and indwelling catheterization is mainly that the catheter may be removed after catheterization in the former, while the catheter is left in the body in the latter. Catheterization is used for urinary retention, recording urine output in acute renal failure, retaining uncontaminated urine for bacterial culture and other tests, and preoperative preparation for various surgeries. The decision to remove the catheter after catheterization is usually made based on the purpose of the catheterization. If there is a need, the catheter is left in place, i.e., the catheter is not removed and a catheterization bag is attached. The risk of urinary tract infection increases when the catheter is left in place, so it is important to take care of the urethral opening as well as to change the catheter regularly during the period of indwelling catheterization to prevent bacterial infections from occurring.