White blood cells (WBCs), also called leukocytes, are immune system cells that defend the body against foreign invaders and inflammation. When infection or inflammation occurs in the urinary tract, the body directs these cells to the site of the problem, leading to their presence in the urine. The detection of WBCs in a urine sample is known as leukocyturia. This common finding indicates irritation within the urinary system. While leukocyturia always warrants further investigation by a healthcare professional, it often points to issues that are highly treatable.
Understanding White Blood Cells in Urine
The standard method for detecting WBCs in urine is routine urinalysis, involving a chemical dipstick test and microscopic examination. The dipstick detects leukocyte esterase, an enzyme released by certain WBCs, providing a quick result. Microscopic analysis provides a direct cell count. A small number of WBCs is considered normal, typically fewer than five cells per high-power field (HPF).
An elevated level of WBCs in the urine, generally defined as ten or more cells per HPF, is known as pyuria. Pyuria signifies an active immune or inflammatory response somewhere along the urinary tract, which includes the kidneys, ureters, bladder, and urethra. The presence of these cells helps clinicians distinguish between a true infection and the simple presence of non-pathogenic bacteria.
Primary Causes of Elevated Levels
Bacterial Infections
The most frequent reason for elevated WBCs in urine is an infection within the urinary tract. Urinary Tract Infections (UTIs) are the most common cause, where bacteria have colonized the bladder or urethra, prompting an intense immune response. A more serious form of infection, pyelonephritis, occurs when bacteria travel up to the kidneys, leading to a much higher concentration of WBCs and more severe systemic symptoms.
Non-Culturable Infections
The immune response can also be triggered by infectious agents that are not routinely detected in a standard urine culture. Certain sexually transmitted infections (STIs), such as those caused by Chlamydia trachomatis or Mycoplasma genitalium, often cause inflammation of the urethra. These organisms require specialized testing because they do not grow on the culture media used for common bacterial UTIs.
Sterile Pyuria (Non-Infectious Causes)
Elevated WBCs without a positive bacterial culture is known as sterile pyuria. This can be caused by non-infectious conditions. Kidney stones, for instance, cause significant inflammation and irritation as they move or obstruct the urinary tract. Other chronic inflammatory conditions, such as interstitial cystitis, can also produce high levels of WBCs. Systemic diseases, including autoimmune disorders like lupus, or inflammation from medications (such as NSAIDs or proton pump inhibitors), may also lead to leukocyturia.
Sample Contamination
External factors can produce a false positive finding of leukocyturia, particularly in women. Contamination of the urine sample with WBCs from vaginal discharge or external skin inflammation is a common issue. This is why a “clean-catch” midstream urine sample is always requested to ensure the specimen accurately reflects what is in the bladder.
Identifying Warning Signs and When to Act
While leukocyturia signals a problem, the accompanying symptoms dictate the urgency of medical attention. Mild irritation or a simple, early-stage bladder infection may present with symptoms such as a mild burning sensation during urination or a slight increase in frequency. In these cases, contacting a healthcare provider for an appointment within a day or two is appropriate.
However, the presence of specific, severe symptoms indicates that the inflammation or infection has progressed and requires prompt action. These severe symptoms warrant an urgent care visit or a trip to the emergency room to prevent potentially serious complications like sepsis or permanent kidney damage.
Signs requiring immediate medical evaluation include:
- A high fever (typically above 101°F) or shaking chills suggests the infection may have entered the bloodstream or reached the kidneys.
- Severe, persistent pain in the flank area, which is the side and back area below the ribs, is a hallmark sign of a kidney infection.
- Nausea, vomiting, or the inability to keep fluids down, which can lead to dehydration and complicate treatment.
- The visible presence of blood in the urine (gross hematuria), coupled with pain or fever, also necessitates immediate medical evaluation.
How Doctors Investigate and Treat the Underlying Issue
The investigation of elevated WBCs begins with a thorough history of symptoms and a repeat urinalysis to confirm the finding and check for nitrites. If the initial test is positive, a urine culture is performed to grow and identify the specific microorganism present. This culture determines the precise type of bacteria and which antibiotics will be most effective for treatment.
If the culture is negative despite pyuria, further testing explores causes of sterile pyuria. This may involve specific tests for STIs or imaging studies (ultrasound or CT scan) to look for kidney stones, obstructions, or structural issues. In complex cases, blood tests may be ordered to check kidney function or systemic inflammation.
Treatment is always directed at the underlying cause. A bacterial UTI is typically resolved with a course of targeted antibiotics, often lasting three to seven days. Kidney stone treatment focuses on pain management and fluid intake, or may require a procedure to remove the stone. Non-infectious conditions, such as interstitial cystitis or drug-induced inflammation, require specialized therapies or adjusting the implicated medication.