Is the urine sterile?

Urine is usually sterile.

Urine is formed from blood, filtered by the kidneys, and waste and excess water are separated from the blood to form raw urine. Subsequently, raw urine is reabsorbed by the renal tubules and further concentrated to become urine. Urine flows into the bladder through the renal pelvis and ureters. When the bladder fills to a certain extent, it stimulates nerves, triggers the urination reflex, and finally passes through the urethra. Bacteria and other microorganisms cannot enter the urinary tract, so urine is normally sterile.

However, when urinary tract infections occur, bacteria may enter the urethra and multiply, resulting in an increase in the number of bacteria in urine.