Pyuria is defined by the presence of an abnormally high concentration of white blood cells (WBCs), or leukocytes, in the urine. It is not a diagnosis itself but a physical sign indicating that the body’s immune system is actively responding to a problem within or near the urinary tract. This presence of immune cells typically signals an underlying issue, most often related to inflammation or infection. While sometimes noticeable through visual changes, pyuria frequently remains undetectable without laboratory testing.
What Pyuria Means
Pyuria represents a localized response by the body’s defense mechanisms, deploying white blood cells (primarily neutrophils) to an affected area. These cells migrate to the urinary tract to combat invading pathogens or clean up damage caused by inflammation. Healthy urine contains a minimal number of these cells, as the urinary system is generally sterile.
A count exceeding a specific threshold formally defines the condition. Pyuria is typically established when a microscopic examination reveals more than five to ten white blood cells per high-power field (WBC/HPF). High concentrations of these cells can cause the urine to appear visibly cloudy or thick, known as macroscopic pyuria. If the elevated cell count is only visible under a microscope, it is known as microscopic pyuria.
Primary Reasons for White Blood Cells in Urine
The presence of leukocytes in the urine is most commonly caused by an active infection within the urinary tract. Bacterial urinary tract infections (UTIs) are the most frequent offenders, as the body sends a cascade of white blood cells to the bladder or urethra to eliminate the bacteria. A more serious form of infection, pyelonephritis, involves the kidneys and can also result in a high level of pyuria, sometimes accompanied by symptoms like fever and flank pain.
Certain sexually transmitted infections (STIs) are also significant contributors, particularly those caused by organisms such as Chlamydia trachomatis and Neisseria gonorrhoeae. These pathogens may not grow on standard bacterial urine cultures, leading to a specific finding called sterile pyuria. Sterile pyuria refers to the detection of white blood cells in the urine despite a negative result on a routine bacterial culture. Other non-bacterial causes of sterile pyuria include:
- Viral infections.
- Recent use of antibiotics that have partially treated an infection.
- Specific medication side effects.
Beyond infectious causes, pyuria can arise from non-infectious inflammatory conditions. The passage of kidney stones can cause irritation and inflammation in the urinary tract lining, which recruits white blood cells to the site. Systemic inflammatory diseases, such as systemic lupus erythematosus (SLE) or Kawasaki disease, may also present with pyuria. Furthermore, inflammation of nearby organs, such as prostatitis in men, can cause white blood cells to enter the urine.
How Pyuria is Detected
The process of detecting pyuria begins with a routine analysis of a urine sample, known as a urinalysis. The first step involves a dipstick test, which uses a chemically treated strip to screen for certain substances. A positive result for leukocyte esterase, an enzyme produced by white blood cells, provides a rapid indication of pyuria. This chemical finding suggests the presence of an elevated level of leukocytes in the sample.
Following the initial screen, the sample is typically examined under a microscope to confirm the finding and precisely quantify the white blood cells. This microscopic examination allows technicians to count the actual number of cells per high-power field, which determines if the clinical threshold for pyuria is met. To ensure accurate results, the patient is often asked to provide a “clean catch” sample, which minimizes contamination from external skin cells or vaginal discharge.
If pyuria is confirmed, a urine culture is usually performed to identify the specific cause. This test involves placing a small amount of the urine sample on a growth medium to see if bacteria or other organisms are present. If the culture grows a significant number of bacteria, a bacterial infection is confirmed, and the laboratory can determine which antibiotics will be effective. If the culture is negative, the medical team will investigate other causes, such as STIs or non-infectious inflammation, to explain the sterile pyuria.
Treating the Source of Pyuria
Treatment for pyuria is entirely dependent on accurately identifying and addressing the underlying cause, as pyuria is a symptom and not a disease itself. If the urine culture confirms a bacterial infection, the appropriate course of action is typically a regimen of antibiotics. The specific type of antibiotic is often selected based on the sensitivity results from the culture, ensuring the medication effectively targets the identified pathogen. Successful treatment of the infection will lead to the resolution of the pyuria.
When the cause is found to be non-infectious, the treatment strategy shifts to managing the primary condition. For pyuria caused by kidney stones, the focus is on managing pain and facilitating the stone’s passage, or employing procedures to remove larger stones. If a systemic inflammatory disease is the source, specialized therapy aimed at modulating the body’s overall immune response would be initiated. In all scenarios, the disappearance of pyuria upon retesting serves as a positive confirmation that the treatment has been effective in resolving the underlying issue.