White Blood Cells in Urine Without Symptoms: Is It an Infection?

Leukocytes are white blood cells. They appear in urine when there is inflammation in the urinary tract or when cells from outside the tract get into the sample. Laboratories report them in several ways: as the number of cells per high-power field in the sediment, as cells per microlitre (analyzers) or semi-quantitatively on a test strip (a reaction for leukocyte esterase, recorded as '+', '++', '+++'). Reference ranges and reporting differ between laboratories, so always compare your result with the range on your own printout.

Practical conclusion: a single, slightly raised leukocyte result in someone without symptoms is very common and means little on its own, especially when the sample may have been contaminated. More important than the count are symptoms, whether the result repeats and the clinical picture. Stamm's paper is old, but it still helps explain methodologically why counting cells per field can be unreliable.

This list is indicative and does not replace medical assessment. It does show, however, that before we get to 'infection' there are many ordinary, harmless explanations.

Especially in women, cells from the vaginal and vulval area get into the urine sample very easily. That is why it is recommended to wash the area around the urethra and collect a midstream sample. Interestingly, the evidence that this ritual actually improves sample quality is weaker than is widely assumed.

What follows? Not that proper collection should be dismissed, but that technique alone does not guarantee a clean sample, and that a single result with many leukocytes and squamous epithelial cells often says more about the sample than about the patient. So when a result is unexpected, a sensible reaction is to repeat it, ideally outside the period, in the morning, after washing the area around the urethra, with a sterile container and a midstream sample, and, if in doubt, with a urine culture.

Asymptomatic bacteriuria means bacteria in the urine without symptoms of infection. It is common: according to the USPSTF document it affects an estimated 1-6% of premenopausal women and 2-10% of pregnant women, and its frequency rises with age. A review of older adults reports that in older women it exceeds 15% and in long-term care facilities reaches as much as 50%. Such figures show that in many people the bacteria in the urine are simply 'lodgers', not a disease.

In line with the logic of that guideline, the mere presence of leukocytes in urine with asymptomatic bacteriuria is not an indication for treatment. Treatment makes sense where the expected benefit outweighs the harm: pregnancy and urological procedures in which the mucosa bleeds. The harms of unnecessary treatment are antibiotic side effects, disruption of the microbiome, Clostridioides difficile infection and rising resistance.

In pregnancy, asymptomatic bacteriuria is an indication for action because, if untreated, it can lead to pyelonephritis, which carries complications for mother and baby. That is why a urine test is routinely ordered in antenatal care and, if abnormal, a culture. It is worth knowing, though, that the evidence is not clear-cut: it comes in large part from old studies.

A 2019 Cochrane meta-analysis (15 trials, over 2,000 women) indicates that antibiotic treatment may reduce the risk of pyelonephritis (RR 0.24), preterm birth and low birthweight, but the certainty of the evidence is low and most trials had a high or unclear risk of bias. Current recommendations (for example the USPSTF) still favour screening in pregnancy, and individual decisions are made by the treating doctor. You should never treat yourself.

In older people, bacteriuria and pyuria are so common that a positive dipstick adds little on its own. The appearance of confusion, a fall or weakness together with a positive strip often leads to an unnecessary antibiotic, although such symptoms have many other causes.

That does not mean an older person with clear symptoms (fever, pain on passing urine, pain in the kidney area) cannot have an infection; they can. The point is that the decision to treat should rest on symptoms and medical assessment, not on the strip result alone.

Sterile pyuria means persistent leukocytes in the urine with a negative routine culture. It is not always truly 'sterile': Stamm described that most symptomatic women with pyuria but without significant bacteriuria had an infection with bacteria in low numbers or with Chlamydia trachomatis, which an ordinary culture does not detect. Other possible causes are earlier antibiotic use, stones, urethritis, interstitial nephritis of the kidney (including drug-induced), urinary tract tuberculosis, bladder lesions including tumors, and inflammation adjacent to the urinary tract.

That is why, with persistent pyuria without bacteria, the doctor usually repeats the test, assesses the sediment, considers a culture for less common organisms, tests for sexually transmitted infections (if there was exposure), reviews medicines, assesses the kidneys (creatinine, eGFR, ACR) and sometimes orders an ultrasound. If pyuria is accompanied by blood in the urine, see our separate article on hematuria.

Limitations: the IDSA and USPSTF guidance is American, and some of the studies it relies on are older. Evidence on treating bacteriuria in pregnancy is of low certainty, and Stamm's study dates from 1983 and concerns methods that have since changed. The principles presented do not apply to children (in whom pyuria with fever needs a different assessment) or to people with a catheter or after an organ transplant, in whom management can differ. This text does not replace a consultation.

The most important change we suggest in how to think about this result is to reverse the order: first the question 'do I have symptoms and am I in a special situation (pregnancy, urological procedure)?', and only then 'what is in the urine?'. Antibiotics are one of the most valuable tools of modern medicine, but every unnecessary use has a price, paid by all of us in the form of resistance. When nothing hurts and leukocytes 'turned up' in a routine test, patience and a repeat test are usually the best strategy.