Pyuria is defined by the presence of an abnormally high number of white blood cells (WBCs), also known as leukocytes, in the urine. This condition is not a disease itself but rather a sign that the body is mounting an immune response, typically indicating inflammation or infection within the urinary tract. The term literally translates to “pus in the urine.” Detecting pyuria points toward an underlying medical condition requiring further investigation and specific treatment.
Understanding the Presence of White Blood Cells in Urine
White blood cells found in urine are the immune system’s primary defense cells, which migrate to the urinary tract to combat irritants or invading pathogens. Pyuria is diagnosed when the concentration of these cells exceeds a threshold, typically defined as ten or more WBCs per cubic millimeter of unspun urine. The presence of these leukocytes is often confirmed through a urinalysis and may cause the urine to appear cloudy or discolored. Clinicians distinguish between pyuria with an active bacterial infection and “sterile pyuria.” Sterile pyuria occurs when the elevated white blood cell count is present, but standard urine culture tests fail to grow significant amounts of common bacteria, suggesting non-bacterial pathogens or non-infectious inflammation.
Primary Causes of Pyuria
Bacterial Infections
The most frequent cause of pyuria is a bacterial urinary tract infection (UTI), affecting the urethra, bladder, or kidneys. When bacteria colonize these areas, the immune system sends white blood cells to neutralize the threat, which are then shed into the urine. A more severe form is pyelonephritis, a kidney infection that causes inflammation of the renal tissue and a significant WBC response.
Sterile Pyuria
Sterile pyuria may be linked to sexually transmitted infections (STIs), such as Chlamydia trachomatis or Neisseria gonorrhoeae, which are difficult to grow on routine culture media. Atypical infections, like genitourinary tuberculosis, can also present with sterile pyuria. Additionally, kidney or bladder stones cause mechanical irritation and inflammation in the urinary tract, resulting in a large influx of WBCs.
Non-Infectious Conditions
Non-infectious causes involve systemic inflammation or direct injury to the urinary organs. Interstitial nephritis, a form of kidney inflammation often triggered by certain medications, causes white blood cell accumulation. Autoimmune disorders, such as systemic lupus erythematosus (SLE), and certain cancers of the urinary tract can also provoke a localized inflammatory response sufficient to cause pyuria.
Symptoms That May Accompany Pyuria
The most common patient complaint is dysuria, a painful and burning sensation experienced during urination. This irritation is often accompanied by the need to urinate more frequently than usual and a sudden, intense urge to pass urine. A visible symptom of pyuria can be cloudy or foul-smelling urine, a direct consequence of the high concentration of leukocytes. If the underlying cause is a more extensive infection, such as pyelonephritis, systemic symptoms may develop. These include fever, chills, and pain in the flank, abdomen, or lower back area.
Diagnosis and Treatment Approaches
The initial detection of pyuria occurs through a urinalysis, where a lab technician checks the urine sample for signs of inflammation, including leukocyte esterase. If pyuria is confirmed, the next step is a urine culture, where the sample is incubated to determine if bacteria are present and to identify the specific type. This testing is essential for guiding treatment, particularly for distinguishing between a bacterial infection and sterile pyuria.
In cases of sterile pyuria or recurrent symptoms, specialized cultures for atypical organisms or STIs may be utilized. Imaging tests, including ultrasounds or CT scans, may also be ordered to visualize the urinary tract for structural issues like kidney stones or blockages. Treatment is entirely dependent on the identified cause of the pyuria. If a bacterial infection is the source, antibiotics are prescribed to eliminate the pathogen. For non-infectious causes, treatment involves managing the underlying condition, or procedures may be necessary to remove physical factors like kidney stones.