Leukocytes in your urine are white blood cells, and their presence usually signals that your body is fighting an infection or inflammation somewhere in your urinary tract. A small number is normal: men typically have fewer than 2 white blood cells per high-power field (HPF) on a microscopy test, and women fewer than 5. Once the count climbs above 10 WBCs per HPF in a symptomatic person, it’s considered abnormal and strongly suggestive of a urinary tract infection.
Why White Blood Cells End Up in Urine
White blood cells are part of your immune system. They normally circulate in your blood, hunting for threats. When bacteria or another irritant reaches your urinary tract, the tissue lining your bladder or kidneys becomes inflamed and sends chemical signals that pull white blood cells out of the bloodstream and into the affected area. Those cells then get flushed into the urine, where a lab test picks them up.
The most common trigger by far is a bacterial urinary tract infection. E. coli causes the majority of UTIs, with Klebsiella, Proteus, and Enterococcus responsible for most of the rest. These bacteria typically travel up the urethra into the bladder, invade the bladder wall, and spark the inflammatory response that floods the urine with white blood cells.
How Leukocytes Are Detected
Most people first learn about leukocytes in their urine from a dipstick test, the quick strip your doctor dips into a urine sample. The strip tests for an enzyme called leukocyte esterase, which white blood cells release. A positive result means white blood cells are present. The dipstick also checks for nitrites, a byproduct of certain bacteria. When both markers are positive together, specificity for a true infection jumps to about 83%, though sensitivity drops to around 52%, meaning some infections will be missed.
If the dipstick is positive or symptoms are strong, the next step is usually a microscopic urinalysis, where a technician examines the urine under a microscope and counts white blood cells per HPF. A urine culture, where the sample is left to grow bacteria in a lab, confirms whether an infection is actually present and which organism is responsible. This matters because leukocytes alone don’t prove infection. Inflammation from other causes can look identical on a dipstick.
Urinary Tract Infections: The Most Common Cause
A bladder infection (cystitis) is what most people with leukocytes in their urine turn out to have. Typical symptoms include a burning sensation when urinating, a frequent urgent need to go, pelvic pressure, and urine that looks cloudy or smells strong. Bladder infections are generally treated with a short course of oral antibiotics, often lasting three to five days. Anti-inflammatory medications like ibuprofen can also help manage symptoms and in mild cases may reduce the need for antibiotics.
When leukocyte counts are very high, typically above 20 WBCs per HPF, and accompanied by fever, back pain, or chills, the infection may have reached the kidneys. This is pyelonephritis, a more serious condition. White blood cell casts, which are clumps of white blood cells molded in the shape of kidney tubules, are a strong clue that the kidneys are involved, though these fragile structures often break apart during lab processing and can be missed.
When There’s No Infection
Sometimes leukocytes show up in urine with no bacteria growing on culture. This is called sterile pyuria, and it has a surprisingly long list of possible causes. Kidney stones are one of the most common, irritating the urinary tract lining enough to draw in white blood cells without any bacteria being involved. Interstitial cystitis (a chronic bladder pain condition) can do the same.
Systemic inflammatory diseases like lupus and sarcoidosis can cause leukocytes to spill into the urine. So can poorly controlled diabetes, certain medications that irritate the kidneys, polycystic kidney disease, and even foreign objects in the urinary tract like stents or surgical mesh. In people who’ve had a kidney transplant, white blood cells in the urine can be an early sign of graft rejection. The point is that a positive leukocyte result doesn’t automatically mean you need antibiotics. The underlying cause determines what happens next.
Leukocytes in Urine During Pregnancy
Pregnancy changes the urinary tract in ways that make infections both more likely and more dangerous. The growing uterus compresses the ureters, slowing urine flow and giving bacteria more time to multiply. A bladder infection that might stay put in a non-pregnant person can more easily climb to the kidneys during pregnancy, raising the risk of serious complications.
For this reason, most prenatal guidelines recommend screening every pregnant person for bacteria in the urine early in pregnancy, usually with a urine culture rather than a dipstick. Dipstick tests during pregnancy have a high rate of false positives and are generally not reliable enough on their own. Even bacteria found without any symptoms (asymptomatic bacteriuria) are typically treated during pregnancy because of the elevated risk of the infection progressing.
What Leukocytes Mean Without Symptoms
If white blood cells turn up in your urine but you feel perfectly fine, the clinical significance depends heavily on your situation. For most healthy, non-pregnant adults, asymptomatic bacteriuria (bacteria in the urine without symptoms) does not need treatment. The Infectious Diseases Society of America specifically recommends against screening for or treating it in healthy women, older adults, people with diabetes, and those with catheters or spinal cord injuries. Treating bacteria that aren’t causing problems can promote antibiotic resistance without providing any benefit.
The two clear exceptions are pregnancy, as noted above, and people about to undergo an invasive urological procedure. In these cases, screening and treatment are recommended even without symptoms. Outside of those scenarios, a trace amount of leukocytes on a routine urinalysis, especially without symptoms, is often a finding that can simply be monitored rather than treated aggressively.
What Your Results Actually Look Like
On a dipstick report, leukocyte esterase is typically reported as negative, trace, small, moderate, or large. “Trace” can be meaningless, especially if you’re not having any urinary symptoms. On a microscopic analysis, results are reported as WBCs per HPF. Under 5 in women and under 2 in men is considered normal. Between 5 and 10 is a gray zone that your doctor will interpret alongside your symptoms. Above 10 in someone with urinary complaints is considered abnormal and usually prompts a culture.
If your results show leukocytes but no nitrites, it could still be an infection (not all bacteria produce nitrites), or it could be one of the non-infectious causes like kidney stones or inflammation. If both leukocytes and nitrites are positive and you have symptoms, a bacterial UTI is the most likely explanation. Either way, a urine culture is the definitive test that tells the full story.