The presence of white blood cells, known as leukocytes, in a urine sample is a common finding during routine diagnostic testing. Leukocytes are a core part of the immune system, migrating to sites of inflammation or infection to neutralize threats. When a high number of these cells are detected in the urine, it signals that the immune system is actively responding to a disturbance along the urinary tract. This finding requires investigation, as the seriousness of leukocytes in urine depends entirely on identifying the specific source of this immune response.
Defining Leukocyturia
The medical term for an abnormally high concentration of leukocytes in the urine is leukocyturia, often referred to as pyuria when the cell count is significantly elevated. Leukocytes enter the urine by shedding from the urinary tract lining, a process triggered by irritation, injury, or the body’s defensive reaction to invading microorganisms.
A standard urinalysis measures these cells using a microscopic examination, counting the number of white blood cells per high-power field (HPF). A count of fewer than five white blood cells per HPF is considered within the normal range. Pyuria is generally defined as a count exceeding five to ten white blood cells per HPF, indicating a clinically significant level of inflammation. The presence of leukocyte esterase, an enzyme found in certain white blood cells, on a urine dipstick test is another common indicator of pyuria.
Common Infectious Causes
The most frequent cause of leukocyturia is a bacterial urinary tract infection (UTI), including infections of the bladder (cystitis) or the urethra (urethritis). When bacteria, such as Escherichia coli, colonize the urinary tract, the immune system recruits large numbers of white blood cells to the infected area, which then pass into the urine. A more severe form is pyelonephritis, where the infection ascends to the kidneys. This kidney infection generates a robust inflammatory response, resulting in a high concentration of leukocytes, often accompanied by systemic symptoms like fever and flank pain.
Pyelonephritis requires prompt medical intervention to prevent long-term kidney damage. Certain sexually transmitted infections (STIs) also frequently cause leukocyturia. Pathogens like Chlamydia trachomatis and Neisseria gonorrhoeae cause urethral inflammation, leading to an influx of white blood cells. In these cases, the urine culture may not detect typical UTI bacteria, leading to a diagnosis of sterile pyuria.
Other Potential Health Concerns
While infection is the most common reason for elevated leukocytes, sterile pyuria—high white blood cell counts without detectable bacteria—is a significant finding. This condition suggests more complex, non-bacterial causes of inflammation within the urinary system. One cause is the presence of kidney or ureteral stones, which are hardened mineral deposits. These stones cause physical irritation or obstruction, drawing leukocytes to the affected site. Chronic inflammatory disorders, such as interstitial cystitis, are another source of sterile pyuria, involving long-term irritation of the bladder wall.
Certain inflammatory kidney diseases, including glomerulonephritis, can also lead to leukocyturia as the immune system attacks the filtering units of the kidneys. Furthermore, systemic autoimmune diseases like Systemic Lupus Erythematosus (SLE) can affect the kidneys, manifesting as leukocyturia. Even some medications, such as certain antibiotics or nonsteroidal anti-inflammatory drugs (NSAIDs), can induce inflammation in the kidney tissue, leading to a temporary increase in urinary leukocytes.
Confirmation and Treatment Approach
When leukocyturia is identified, the immediate next step is to confirm the underlying cause through targeted diagnostic tests. A urine culture is the most common follow-up procedure, used to isolate and identify bacteria and determine their sensitivity to antibiotics. If the culture is positive, a short course of the appropriate antibiotic is typically prescribed to eliminate the bacterial infection and resolve the leukocyturia. If the urine culture returns negative results (sterile pyuria), further testing is necessary. This may involve specialized tests for less common pathogens like tuberculosis or STIs, or imaging studies such as ultrasound or CT scans to look for kidney stones, obstructions, or structural abnormalities.
Treatment for non-infectious causes focuses on managing the primary condition responsible for the immune response. For conditions like kidney stones, this may involve removal procedures or medications to aid their passage. Management of chronic inflammation or systemic diseases may include anti-inflammatory medications or immunosuppressive drugs to control the underlying disorder.