Pyuria (White Blood Cells in Urine): Causes & Treatment

Pyuria is a term that describes the presence of pus, which is mostly made up of white blood cells, in urine. Urine typically contains very few or no white blood cells. The most common cause of pyuria is a urinary tract infection (UTI), but other conditions can also cause it. Pyuria may also occur as a side effect of some medications. 

Some people with pyuria have no noticeable symptoms, though others may experience symptoms depending on the underlying cause. Treatment focuses on addressing what’s causing pyuria.

Pyuria is classified based on its underlying cause and urine test results, which check for bacteria and white blood cells in urine.

Non-Sterile Pyuria 

Non-sterile pyuria involves the presence of white blood cells and bacteria in urine. This is typically a sign of a UTI. A UTI can cause pyuria, but having non-sterile pyuria doesn’t necessarily mean you have a UTI. 

Sterile Pyuria

Sterile pyuria means there are white blood cells in your urine, but no clear signs of bacteria causing an infection. This can happen for several reasons, such as taking certain medications or having non-infectious conditions like kidney stones, kidney disease, or diabetes. Some people with sterile pyuria may still have an infection, including sexually transmitted infections (STIs).

Due to the presence of white blood cells, pyuria can cause noticeable changes in urine, making it appear cloudy with a strong or foul-smelling odor.

Because pyuria is a sign of an infection or underlying condition, symptoms can vary widely depending on the cause. Symptoms of conditions that commonly cause pyuria, such as urinary tract infections, kidney stones, or underlying conditions like tuberculosis, can include:

• Pressure, pain, or cramping in your lower abdomen or back 
• Frequent urination
• Pain or burning sensation with urination
• Fever
• Flank pain (discomfort in your back, side, or pelvic area) 
• Nausea 
• Vomiting 
• Blood in your urine (hematuria)
• Fatigue 

Pyuria occurs when excess white blood cells are present in the urine. White blood cells are part of the immune system and help detect and fight bacteria, viruses, fungi, parasites, and other irritants causing inflammation or infection. With pyuria, your body sends white blood cells to the urinary tract in response to infection or inflammation.

The most common cause of pyuria is a urinary tract infection (UTI), which occurs when bacteria enter the urinary tract through the urethra and multiply in the bladder or other parts of the urinary system. This prompts your immune system to send white blood cells to fight the infection. 

In sterile pyuria, white blood cells are present in urine without detectable bacteria. Some potential causes of sterile pyuria may include: 

• Sexually transmitted infections (STIs), such as chlamydia and gonorrhea
• Kidney stones
• Genitourinary tuberculosis
• Medications, including nonsteroidal anti-inflammatory drugs (NSAIDs), proton pump inhibitors (PPIs), and diuretics (water pills) 
• Radiation therapy in the pelvic or genital region 
• Parasitic and fungal infections 
• Polycystic kidney disease 
• Kawasaki disease 
• Diabetes 
• Systemic lupus erythematosus (SLE)
• Tumor in the urinary tract
• Pregnancy

Risk Factors

Anyone can develop pyuria and associated conditions, but certain factors can increase the risk. These include: 

• Sex: Women and people assigned female at birth (AFAB) are more likely to develop urinary tract infections. UTIs are more common in women because their urethras are shorter and closer to the anus, making it easier for bacteria to travel to the bladder. Hormonal changes, such as during pregnancy or menopause, and sexual activity also increase the risk.
• Underlying conditions: People with certain conditions, such as diabetes, chronic kidney disease, kidney stones, or autoimmune conditions like lupus and Kawasaki disease, have an increased risk of pyuria.
• Age: Older adults may be at an increased risk of UTIs due to age-related changes in their immune system.
• Recent medical procedures: Recently using a catheter to drain urine or undergoing surgeries in the abdominal or genital region can introduce bacteria to the urinary tract and increase your risk of pyuria. 

Diagnosing pyuria involves identifying white blood cells in your urine and determining the underlying cause. Your healthcare provider will review your medical history and ask about your symptoms. They will likely order diagnostic tests to confirm pyuria and determine the cause.

A urinalysis (urine test) can help your healthcare provider detect and measure the amount of white blood cells in your urine. Healthcare providers generally diagnose pyuria when there are 10 or more white blood cells per microliter (µL) of urine or more than three white blood cells seen under a high-powered microscope field.

To determine what’s causing pyuria, your healthcare provider may order additional testing, such as: 

• Urine culture: This test identifies the specific bacteria or fungi causing an infection.
• Blood tests: A blood sample can help your healthcare provider check for and measure markers of inflammation and infection and evaluate your kidney function.
• Imaging tests: Such as ultrasound and computed tomography (CT) scans, help visualize your kidneys, bladder, and other internal structures and organs to detect structural differences, kidney stones, or other abnormalities.

Treatment for pyuria focuses on addressing the underlying cause to relieve symptoms, reduce inflammation, and irritation in the urinary tract. The treatment approach may depend on whether your pyuria is sterile or non-sterile. 

Prescription Medications

If a urinary tract infection is causing pyuria, your healthcare provider will likely prescribe antibiotics to eliminate the bacteria and clear the infection. Antibiotics can also treat sexually transmitted infections that can cause pyuria, including chlamydia and gonorrhea.

Otherwise, antifungal medications can be used to treat fungal infections in the urinary tract. Anti-inflammatory drugs can treat interstitial cystitis or other inflammatory causes.

If your healthcare provider suspects that a medication you take is causing pyuria, they may ask you to stop taking the medication or prescribe a different one.

Medical Procedures

If kidney stones are causing pyuria and the stones are too large to pass or they block the flow of urine, surgical removal may be necessary. Shock-wave lithotripsy is a noninvasive treatment that uses powerful sound waves to break the stone into smaller pieces, making it easier to pass them through urine. 

Ureteroscopy involves inserting a thin scope through the ureter (a tube that carries pee outside of your body) to either remove or break apart the stone. A procedure called percutaneous nephrolithotomy or nephrolithotripsy may be necessary for larger stones. These procedures involve making a small incision in the back and inserting a thin tube into your kidney to remove or break the stone into smaller pieces before removing it.

It may not always be possible to prevent pyuria, but certain lifestyle habits that support your urinary tract health can help lower your risk of infections and other causes of pyuria. These lifestyle strategies include:

• Stay hydrated: Drink plenty of water to help flush out bacteria and lower your risk of UTIs. Hydration can also help prevent kidney stones.
• Practice good hygiene: Keeping your genitals clean after using the bathroom can lower your risk of UTIs. For those with a vulva, this involves wiping front to back to avoid spreading bacteria from the anus to the urethra. 
• Urinate after sexual activity: Peeing after sexual activity helps prevent bacteria from entering the urethra. 
• Manage chronic conditions: Follow your treatment plan for underlying conditions such as diabetes, which can increase your risk of pyuria.
• Empty your bladder: Urinating when you feel the urge to go, rather than holding it in, can help lower your risk of UTIs that cause pyuria.

Conditions that cause pyuria typically require treatment. Without treatment, complications can develop. These may include:

• Kidney infections (pyelonephritis): Untreated infections in your lower urinary tract can move to the kidneys, causing significant pain, fever, and potential kidney damage.
• Sepsis: In severe cases, untreated infections can enter the bloodstream, causing a life-threatening systemic response known as sepsis.
• Bladder dysfunction: Persistent or recurrent UTIs may weaken your bladder function over time, leading to incontinence (loss of bladder control).

Pyuria, the presence of white blood cells in your urine, is often a sign of an underlying issue such as a urinary tract infection or inflammation in the urinary system due to kidney stones or other conditions. Common symptoms include cloudy or foul-smelling urine, painful urination, and frequent urges to urinate. A urinalysis (urine test) can diagnose pyuria and help identify its cause.

Treatment focuses on addressing the root cause, such as antibiotics for infections or other therapies for non-infectious causes. Staying hydrated and practicing good hygiene can help lower your risk of UTIs and pyuria. Talk to a healthcare provider if you’re experiencing painful urination, cloudy urine, or lower abdominal or back pain.