White blood cells are the specialized cells in the blood responsible for fighting infections and providing the body with immunity. The kidneys filter about 200 quarts of blood a day, according to The National Kidney and Urologic Diseases Information Clearinghouse, to separate the waste and excess fluids from the blood. Normal, healthy urine does not contain white blood cells. However, certain conditions may cause white blood cells in urine.
Urinary Retention
Urinary retention is the inability to completely empty the bladder. Acute urinary retention is the complete inability to empty the bladder and is a medical condition that requires immediate treatment. Chronic urinary retention is characterized by difficulty starting to urinate and the inability to void all the urine in the bladder. This is most common in men as it is often a symptom of prostate enlargement, but it can also occur in women.
When the bladder is unable to empty completely, the urine can back-flow into the kidneys. This can cause damage to the kidneys, which can interfere with their ability to effectively filter the blood. White blood cells may then leak into the urine.
Inflammation
Inflammation occurs when there is damage to tissues, often caused by bacteria, toxins or trauma. The damaged tissue releases a variety of chemicals including histamines, which dilate blood vessels, and serotonin. These chemicals cause the fluids to leak out of nearby blood vessels, thereby isolating the foreign substance and protecting surrounding tissues.
The release of these chemicals also attracts white blood cells to the area. These cells function to engulf the foreign particles as well as the dead and damaged cells. Therefore, any inflammation of the urinary tract, including the kidneys, bladder or urethra, can cause white blood cells to be present in the urine.
Infections
A urinary tract infection (UTI) is an infection that affects any part of the urinary system, including the bladder, ureters, urethra and kidneys. A UTI is caused by the presence of bacteria and can cause urinary urgency, a burning sensation during urination, cloudy urine and blood (including white blood cells) in the urine.
Urinary tract infections are more common in women. In fact, according to doctors at the Mayo Clinic, approximately half of all women will have a UTI sometime in her life. This is due to a woman's anatomy, in that her urinary opening and rectum are in close proximity, which allows bacteria from the stools to contaminate the urethra. In addition, a woman's urethra is much shorter than a man's and that means the bacteria does not have far to travel to reach the bladder.
