The presence of “pus cells” in a urine sample is medically defined as pyuria. These cells are leukocytes, which are white blood cells. Pyuria indicates an inflammatory or immune response taking place somewhere along the urinary tract. While the finding can be alarming, it is a common indication that the body is fighting off an infection or reacting to irritation. Identifying the underlying cause is the necessary next step, as pyuria is a sign of an issue rather than a diagnosis.
What Leukocytes Are and How They Are Measured
Leukocytes are immune cells produced in the bone marrow, functioning as the body’s primary defense against foreign invaders like bacteria and viruses. When infection or inflammation occurs in the urinary system, these white blood cells migrate to the site to neutralize the threat. Their presence in the urine is a direct sign of localized immune activity.
The quantification of leukocytes in urine is done through a urinalysis. A standard microscopic examination of a centrifuged urine sample measures the number of white blood cells per high-power field (HPF). A normal result is considered five or fewer white blood cells per HPF. Pyuria is diagnosed when the count exceeds this threshold, often defined as ten or more white blood cells per cubic millimeter of urine or six to ten or more neutrophils per HPF. This elevated count signals a significant immune response within the urinary tract.
Common Conditions That Cause Pyuria
The most frequent cause of elevated leukocytes in urine is a bacterial Urinary Tract Infection (UTI), affecting the urethra, bladder, or kidneys. These infections, often caused by Escherichia coli, trigger a strong immune response, flooding the urinary tract with white blood cells. A lower tract infection, such as cystitis, typically results in pyuria alongside symptoms like painful and frequent urination.
When the infection ascends to the kidneys, known as pyelonephritis, the pyuria is often more severe and accompanied by systemic symptoms. This kidney infection is more serious and can lead to flank pain, fever, and nausea. The presence of leukocytes marks the kidney tissue’s inflammatory reaction to the bacterial invasion.
Another infectious cause is Sexually Transmitted Infections (STIs), particularly those that do not grow on standard bacterial cultures. Conditions like chlamydia and gonorrhea cause inflammation in the urethra, leading to pyuria without typical UTI-causing bacteria. This finding, where leukocytes are present but routine culture is negative, is known as sterile pyuria.
Non-infectious conditions can also irritate the urinary system enough to draw white blood cells into the urine. Kidney stones cause mechanical irritation and inflammation as they move through the urinary tract, resulting in pyuria. The rough edges of the stone create a persistent inflammatory response, causing leukocytes to appear.
Certain kidney diseases, such as interstitial nephritis, involve inflammation within the kidney tissue that results in pyuria. This can occur as a reaction to certain medications, including some nonsteroidal anti-inflammatory drugs (NSAIDs) or specific antibiotics. Autoimmune disorders like systemic lupus erythematosus can also cause inflammation in the kidney, known as lupus nephritis, leading to a high leukocyte count. In these cases, pyuria is a sign of inflammation rather than a bacterial fight.
Diagnostic Steps to Identify the Cause
Once pyuria is detected, a healthcare provider initiates a diagnostic process to pinpoint the source of inflammation. The initial assessment begins with a urine dipstick test, which quickly screens for leukocyte esterase, an enzyme present in white blood cells. A positive result suggests the presence of leukocytes and prompts further detailed testing.
Following the dipstick, a microscopic analysis confirms the number of leukocytes and determines if red blood cells or casts are present, which can indicate kidney involvement. If an infection is suspected, a urine culture and sensitivity test is performed. This test identifies the specific type of bacteria or fungus causing the issue and determines which antibiotics will be most effective.
In cases of sterile pyuria (culture negative) or recurrent issues, more specialized testing is required. Physicians may test for less common pathogens, such as those causing STIs or genitourinary tuberculosis, which require specific culturing techniques. Imaging studies, such as an ultrasound or CT scan, may be used to check for structural problems like kidney stones, tumors, or blockages in the urinary tract causing irritation.
Addressing the Underlying Condition
Treatment for pyuria depends entirely on the cause identified through the diagnostic workup. If a bacterial infection, such as a UTI or pyelonephritis, is confirmed by a positive culture, the standard approach involves a course of antibiotics. Patients must complete the full prescription to ensure the infection is eradicated and to prevent antibiotic resistance.
For non-bacterial infections, such as those caused by a virus or a fungus, specific antiviral or antifungal medications are prescribed. If pyuria is due to a non-infectious cause like kidney stones, management focuses on pain control and facilitating the stone’s passage, or using procedures to break it up or remove it. Structural issues or tumors may require surgical intervention or other specialized treatments.
If the cause is linked to an underlying inflammatory condition or a medication side effect, treatment may involve anti-inflammatory drugs or adjusting the dosage or type of medication. Consulting a healthcare provider for a proper diagnosis is necessary to determine the appropriate treatment plan. Treating the root cause is how pyuria is ultimately resolved.