The presence of abnormal levels of leukocytes, or white blood cells, in a urine sample is known as pyuria. Leukocytes are the body’s immune defense cells, and their appearance signals an inflammatory response or an active infection somewhere along the urinary system, from the kidneys to the urethra. This finding is typically the result of a routine urinalysis. While a small number of white blood cells is normal, an elevated count indicates the body is actively mobilizing its defenses. Pyuria is a common finding that directs a healthcare provider toward a focused investigation into the underlying cause.
Understanding the Test Result
The detection of white blood cells in urine involves a dipstick test and microscopic examination. The dipstick screens for leukocyte esterase, an enzyme released by white blood cells, and a positive result suggests their presence. For precise measurement, a laboratory technician examines the urine under a microscope. Pyuria is generally defined as more than five white blood cells per high-power field (WBC/HPF) in a centrifuged urine sample.
Pyuria is differentiated into two types. Non-sterile pyuria occurs when the elevated white blood cell count is accompanied by a positive urine culture, confirming a bacterial infection. Sterile pyuria is the presence of white blood cells without significant bacterial growth in a standard culture. This distinction is important for determining the correct next course of action.
Common Infectious Causes
The most frequent cause of abnormal leukocytes in urine is a bacterial urinary tract infection (UTI). This infection can be localized to the bladder (cystitis) or the urethra (urethritis). The immune system sends white blood cells to the site of the bacterial invasion, and these cells are then shed into the urine.
A related infectious cause is pyelonephritis, a bacterial infection that has ascended to the kidneys. Pyelonephritis often presents with severe symptoms, such as fever, chills, and flank pain. The presence of white blood cell casts in the urine can specifically point to this diagnosis. Beyond typical UTIs, certain sexually transmitted infections (STIs) like chlamydia, gonorrhea, and trichomoniasis cause inflammation in the urethra, resulting in sterile pyuria.
Non-Infectious and Chronic Contributors
When the urine culture is negative, the search turns to causes of sterile pyuria that are not simple bacterial infections. One common source is irritation or inflammation of the urinary tract caused by kidney stones, also known as renal calculi. These stones create physical trauma and blockages, triggering an inflammatory response that draws white blood cells to the area.
Certain systemic diseases that affect the body’s immune system can also manifest as pyuria. Conditions like systemic lupus erythematosus (SLE) or Kawasaki disease can cause inflammation in the kidneys, leading to an elevated white blood cell count in the urine. Inflammation of the kidney tissue itself, known as interstitial nephritis, is often a reaction to certain medications, including some antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs), and diuretics.
Contamination of the sample is another important consideration, particularly in female patients, where vaginal discharge or menstrual blood can introduce leukocytes into the urine specimen. Finally, chronic, atypical infections, such as genitourinary tuberculosis, can cause persistent sterile pyuria and require specialized diagnostic testing.
Next Steps in Diagnosis and Treatment
Once abnormal leukocytes are found, the next steps focus on pinpointing the exact cause to guide treatment. The most immediate follow-up test is a urine culture and sensitivity test, which attempts to grow any bacteria present in the sample to identify the specific pathogen. The sensitivity part of the test determines which antibiotics are effective against the identified bacteria.
If the culture is positive, treatment typically involves a targeted course of antibiotics to eliminate the bacterial infection. If the culture is negative, the healthcare provider will often order further investigations based on the patient’s symptoms and medical history. Imaging studies, such as an ultrasound or CT scan, may be necessary if an obstruction, like a kidney stone or a tumor, is suspected as the source of inflammation.
Treatment in cases of sterile pyuria depends on the underlying issue identified. For drug-induced interstitial nephritis, the treatment involves stopping the offending medication. If a systemic inflammatory condition like Lupus is the cause, management of the underlying autoimmune disease is required. Effective treatment involves addressing the root cause of the body’s immune response.