Is urine sterile? Most people think of urine as being a fluid that’s inherently “yucky,” but normal urine is surprisingly free of bacteria and other organisms. If you took a urine sample directly from a healthy person’s bladder that doesn’t have a urinary tract infection, it would be free of bacteria, yeast and other organisms. But as urine moves from the bladder, it enters a tube called the urethra that connects with the outside of the body. During this journey, it can become contaminated with bacteria that reach the urethra from the outside. This is more common in women because their urethra lies closer to the opening of their anus, making it easy for anal bacteria to gain entry to the urinary tract through the urethral opening. Women also have shorter urethras than men. This puts them at higher risk for urinary tract infections.
Is Urine Sterile: Is Non-Sterile Urine a Sign of a Urinary Tract Infection?
When bacteria enter the urethra from outside the body, they can multiply and set up an infection. One way a doctor looks for a urinary tract infection is to check a urine sample for bacteria and white blood cells. In some cases, red blood cells also enter the urine when there’s an infection. A chemical test may also be used to check for urine nitrites.
Bacteria in the urine without white blood cells or red blood cells doesn’t always mean a person has an infection. Sometimes urine becomes contaminated with bacteria during the collection process. That’s why doctors tell patients to wash around their urethra before taking a urine specimen to remove any outside bacteria and then collect only the mid-portion of the urine stream since it’s less likely to be contaminated with bacteria from the outside. It’s also important to use a sterile container to avoid contamination.
Urine Cultures Confirm the Diagnosis of Urinary Tract Infection
In some cases of suspected urinary tract infection, a doctor sends the urine for culture to see what type of bacteria grow up. This helps to confirm the diagnosis and gives the doctor guidance as to the best treatment since the bacteria can be tested to see how sensitive they are to different antibiotics. In cases where the diagnosis is obvious, a urine culture may not be necessary.
Is Urine Sterile: The Bottom Line?
Urine from the bladder is typically devoid of bacteria and other organisms unless a person has a urinary tract infection. Once urine travels into the urethra, the tube that leads out of the bladder to the outside, it can become contaminated with bacteria from outside the body. In some cases, these bacteria can proliferate in number, leading to a urinary tract infection. This usually requires antibiotic treatment to eliminate the infection and relieve the symptoms.
References:
Merck Manual. Eighteen Edition. 2006.
WebMD. “Urine Culture”