Leukocytes in urine: why do they increase?

Leukocytes in urine indicate that inflammatory cells were detected in the urinary sediment or during rapid analysis. This fact alone is not a diagnosis. It only indicates that somewhere in or near the urinary tract there is an inflammatory process, infection, irritation of the mucous membrane, or an admixture of cells from the external genital tract. Therefore, leukocytes in urine should not be interpreted in isolation, but in conjunction with complaints, bacteria, red blood cells, protein, nitrites, urine culture results, and the method of urine collection. [1]

Two terms are used for this finding. Leukocyturia refers to an increased number of leukocytes in the urine. Pyuria is a more severe form, in which there are numerous leukocytes, the urine sometimes becomes cloudy, and in severe inflammation, it may contain visible pus. However, there is no single, universal threshold for all laboratories and all methods: some sources define pyuria as more than 5 leukocytes per field of view, while others define it as more than 3 leukocytes in uncentrifuged urine or a positive leukocyte esterase on a test strip. [2]

In practice, the most common cause of leukocytes in urine is a urinary tract infection. But this is far from the only possible cause. Leukocytes can appear due to stones, kidney inflammation, interstitial nephritis, sexually transmitted infections, catheters, tumors, and also due to improper urine collection, when leukocytes from vaginal discharge or the surface of the external genitalia enter the sample. [3]

It is crucial not to confuse leukocyturia with the absolute need for antibiotics. International guidelines emphasize that asymptomatic bacteriuria is defined as the presence of bacteria in the urine without symptoms of infection and is considered independent of the presence of pyuria. In other words, even the presence of bacteria and leukocytes without symptoms does not necessarily necessitate antibiotics in most patient groups. [4]

There are exceptions, but they are few. Screening and treatment of asymptomatic bacteriuria are recommended primarily for pregnant women and patients undergoing urological procedures that disrupt the urinary tract mucosa. In many other situations—healthy non-pregnant women, most elderly patients, people with diabetes, patients with catheters, or after kidney transplantation—routine treatment of asymptomatic findings is not indicated. [5]

Table 1. What the detection of leukocytes in urine can mean in principle

Find	What does this mean in practice?
A small number of leukocytes without complaints	may be a normal variant or a consequence of contamination
Leukocytes plus dysuria, frequent urination, pain	urinary tract infection is likely
Leukocytes plus negative standard culture	sterile pyuria is possible
Leukocytes in a pregnant woman without symptoms	a culture and separate obstetric tactics are needed
Leukocytes in an elderly person without local symptoms	You can't automatically diagnose an infection
Leukocytes in a patient with a catheter	The test strip is uninformative; symptoms and culture are important.

The meaning of the table is based on urological, infectious, obstetric and clinical recommendations of recent years. [6]

Why do leukocytes in urine increase?

The most common cause is a bacterial infection of the lower or upper urinary tract. Cystitis typically presents with a burning sensation during urination, frequent urination, and discomfort above the pubis. With pyelonephritis, leukocyturia is accompanied by fever, lower back pain, chills, weakness, and sometimes nausea and vomiting. It is precisely when symptoms are present that infection becomes the most likely explanation for the test. [7]

The second major group of causes is non-infectious inflammation and irritation of the urinary tract. These include urolithiasis, obstruction, interstitial nephritis, inflammatory systemic diseases, radiation damage to the bladder, reactions to contrast agents, catheters, and other iatrogenic factors. In these conditions, leukocytes are present, but antibiotics may not only fail to help but also distract from the real cause. [8]

Sterile pyuria is a particular concern. This is the condition where leukocytes are detected, but standard cultures show no significant bacterial growth. This is not uncommon and is not a "laboratory whim." Causes may include recently started antibiotics, sexually transmitted infections, genitourinary tuberculosis, inflammatory diseases of adjacent organs, immune and systemic processes, and sometimes simply poor urine collection. [9]

In women, false leukocyturia is more common due to the presence of vaginal discharge. In men, it is less common, but can also occur if the sample is collected incorrectly. Therefore, a single "bad" result without symptoms should not be treated; instead, a recheck should be performed with a properly collected midstream urine sample. This step is often more beneficial than an immediate repeat course of antibiotics. [10]

Another common diagnostic error is interpreting urine leukocytes as a universal marker of infection in the elderly. Asymptomatic bacteriuria is common in older adults, and the specificity of tests decreases. Therefore, a positive test in a person over 65 years of age without new local urinary symptoms or signs of systemic infection should not automatically lead to a diagnosis of cystitis. [11]

Table 2. Main causes of leukocytes in urine

Group of reasons	Examples
Infectious	cystitis, pyelonephritis, urethritis, prostatitis
Sterile pyuria of infectious origin	sexually transmitted infections, genitourinary tuberculosis, recently started antibiotics
Non-infectious urological	stones, obstruction, catheter, radiation cystitis
Renal and immune	interstitial nephritis, systemic lupus erythematosus, sarcoidosis
Technical and false	sample contamination, admixture of vaginal leukocytes
Special clinical contexts	pregnancy, old age, long-term catheter

The table summarizes the modern differential diagnosis of leukocyturia and sterile pyuria. [12]

Symptoms and when white blood cells in urine are actually dangerous

Leukocytes themselves are not felt in urine. Symptoms are caused by the underlying disease. A lower urinary tract infection typically causes burning, stinging, frequent urination, urgency, lower abdominal discomfort, and sometimes an unpleasant urine odor. Without such symptoms, the diagnostic value of leukocyturia alone is significantly reduced. [13]

The combination of leukocytes in the urine with fever, chills, lower back pain, nausea, or vomiting requires special attention. This suggests a lesion of the upper urinary tract, particularly pyelonephritis. In these cases, not only a general urine analysis is necessary, but also a urine culture, and often a more active evaluation for complications and, if indicated, urinary tract imaging. [14]

If leukocyturia is accompanied by blood in the urine, colicky flank pain, difficulty passing urine, or severe unilateral pain, one must consider a stone, obstruction, or a combination of a stone and infection. This situation may require not only antibacterial treatment but also urgent urological care. [15]

There is also a scenario where there are no local urinary complaints, but the test still shows "inflammatory" results. In this case, it's important to consider sterile pyuria, systemic diseases, drug-induced kidney injury, appendicitis, diverticulitis, and other conditions in which leukocytes appear in the urine secondarily. Therefore, a diagnosis based on a single test form without a history or examination can be false. [16]

Prompt in-person evaluation is especially important in patients with a combination of fever, low back pain, decreased urine output, confusion, pregnancy, male gender with acute symptoms, childhood with high fever, and the presence of an indwelling catheter. In these groups, the likelihood of complicated infection and self-diagnosis error is higher than in a healthy young woman with typical uncomplicated cystitis. [17]

Table 3. When the situation requires an expedited examination

Situation	Why is this important?
Temperature plus lower back pain	pyelonephritis is possible
Leukocytes plus colic and blood in the urine	possible stone or obstruction
Pregnancy plus leukocyturia or symptoms	higher risk of complications for mother and fetus
Elderly people without local symptoms but with a positive strip	there is a high risk of overdiagnosis; clinical selection is needed
Indwelling catheter and suspected infection	The test strip is unreliable; a different approach is needed.
A child with fever and abnormal urine	timely collection of urine and confirmation by culture is necessary

The table is based on urological, obstetric, pediatric and clinical guidelines.[18]

How to correctly diagnose and interpret the results

Diagnosis begins not with an antibiotic, but with a proper urine sample. For adults, the standard is a clean midstream urine sample. If the sample is improperly collected, the laboratory may detect leukocytes, epithelial cells, and even mixed bacterial growth, which reflect contamination rather than disease. If contamination is suspected, the test should be repeated rather than attempting to treat the numbers.

The rapid dipstick test is useful for initial diagnosis because it detects leukocyte esterase and nitrites. However, it cannot be considered a definitive diagnosis. In pregnant women, pyuria, defined as more than 5 leukocytes per high-power field or the presence of leukocyte esterase, has a high sensitivity of up to 97%, but low specificity because leukocytes can be present in the sample from the vulva and vagina. Therefore, a positive dipstick is a reason for further investigation rather than automatic treatment. [20]

For adults with suspected urinary tract infection, routine testing includes a urinalysis, sediment microscopy if necessary, and, depending on the clinical situation, urine culture. European urology guidelines recommend performing a urinalysis, including assessment of white and red blood cells and nitrites, for routine diagnostics, and, in cases of pyelonephritis, mandatory culture and antibiotic susceptibility testing. [21]

A crucial principle of modern diagnostics is that pyuria helps to exclude infection rather than confidently confirm it. A 2024 study showed that positive urinalysis parameters have a weak positive predictive value for diagnosing urinary tract infection, and their diagnostic accuracy is particularly low in elderly women. Therefore, leukocytes in urine without appropriate symptoms are a weak argument for antibiotic use. [22]

For sterile pyuria, the algorithm is different. First, a collection error is ruled out and the analysis is repeated. Then, recent antibiotic use, sexual history, risk of sexually transmitted infections, risk of urogenital tuberculosis, drug exposures, systemic diseases, and the need for renal and urinary tract imaging are assessed. If sexually transmitted infections are suspected, testing for chlamydia and gonococcal infection is recommended, and if there are epidemiological risk factors for tuberculosis, three consecutive urine samples are required for specific testing. [23]

Table 4. How to read the main urine test options

Find	The most probable meaning
Leukocyte esterase is positive	there are leukocytes or their enzymes, but the cause is not yet clear
Nitrites are positive	the risk of bacterial infection increases
There are leukocytes, the culture is positive, there are complaints	urinary tract infection is likely
There are leukocytes, but the culture is negative.	sterile pyuria or collection error is possible
There are leukocytes, no complaints	You can't automatically diagnose cystitis.
Leukocytes plus epithelial cells and mixed growth	possible contamination

The table reflects the practical interpretation of general urine analysis, dipstick testing and culture. [24]

Table 5. What additional studies are needed depending on the situation

Situation	What do they usually do next?
Typical cystitis in a non-pregnant woman	urine analysis, sometimes culture depending on the clinical situation
Fever and lower back pain	urine culture, assessment for pyelonephritis, visualization if indicated
Pregnancy	urine culture, separate obstetric tactics
Sterile pyuria	repeat testing, evaluation for sexually transmitted infections, tuberculosis, medications, stones
Catheter	clinical evaluation, culture, not test strip
Child	properly collected urine before starting antibiotics, confirmed by culture

The table summarizes the differences in diagnostic tactics in adults, children, pregnant women and catheterized patients. [25]

Treatment: When antibiotics are needed and when they are not

It's not the leukocytes in the urine that are treated, but the underlying cause. If a patient has typical symptoms of infection and supporting laboratory data, treatment is directed against the infection. If leukocytes are detected incidentally without complaints, the treatment may not involve medication, but rather repeat testing, culture, observation, or a search for another cause of the inflammation. This principle underlies the modern strategy of rational antibiotic use. [26]

In uncomplicated lower urinary tract infections, treatment decisions are based on the clinical picture and the likelihood of a bacterial process. However, even in this classic situation, the goal of therapy is to stop a confirmed or highly probable infection, not to normalize the test results at any cost. After symptoms resolve, routine repeat testing is not required in many adults, unless the course was atypical or complicated. [27]

With asymptomatic bacteriuria, the situation is reversed. International guidelines clearly state that it does not need to be routinely screened and treated in most non-pregnant adults, including postmenopausal women, patients with diabetes, elderly people in long-term care facilities, and many other groups. This rule applies regardless of the presence of pyuria, because pyuria itself does not transform asymptomatic bacteriuria into an infection requiring antibiotics. [28]

The main exceptions are pregnancy and urological procedures that disrupt the mucosa. During pregnancy, urine culture screening is recommended once during early prenatal care. If asymptomatic bacteriuria is confirmed, treatment reduces the risk of pyelonephritis and adverse pregnancy outcomes. Asymptomatic bacteriuria is also treated before urological procedures that traumatize the mucosa, as this reduces the risk of postoperative infectious complications. [29]

If the cause of leukocyturia is not bacterial, antibiotics are ineffective. In sterile pyuria, the underlying condition must be treated: sexually transmitted infections, genitourinary tuberculosis, drug-induced interstitial nephritis, stones, a systemic inflammatory disease, or the underlying technical cause. Therefore, with a negative culture and persistent leukocyturia, the primary goal is not to "select a stronger antibiotic," but to complete the differential diagnosis. [30]

Table 6. When antibiotics are usually indicated and when they are not

Situation	Antibiotics are usually needed	Comment
Symptomatic urinary tract infection	Yes	treat confirmed or clinically probable infection
Pyelonephritis	Yes	a culture is needed; in severe cases, a more active tactic is needed
Asymptomatic bacteriuria in non-pregnant adults	No	pyuria itself does not change this
Asymptomatic bacteriuria in a pregnant woman	Yes	This is one of the key exceptions.
Before urological intervention with mucosal damage	Yes	treatment reduces the risk of complications
Sterile pyuria without evidence of bacterial infection	not automatically	First, we need to find the cause.

The table is based on infectious, urological and obstetric recommendations. [31]

Special situations: pregnancy, children, the elderly and catheters

Pregnancy is a special group because the consequences of missing an infection are higher. The American College of Obstetricians and Gynecologists recommends performing a urine culture early in pregnancy to screen for asymptomatic bacteriuria. In symptomatic cystitis, pyuria or leukocyte esterase are sensitive indicators, but are not specific enough on their own, so urine culture and clinical evaluation remain crucial. [32]

In children, proper specimen collection is also crucial. Clinical guidelines for pediatric practice emphasize that urine should be obtained before antibiotic administration, and bag-type collection tubes are not suitable for culture due to the high rate of false-positive results. For young children, clean collection, catheterization, or suprapubic aspiration are used, depending on age and condition. [33]

In older adults over 65 years of age, a positive dipstick test is often misleading because asymptomatic bacteriuria becomes increasingly common with age. British guidelines explicitly advise against using dipstick testing as the primary diagnostic method for urinary tract infection in this group. Clinical decisions should be based on new local urinary symptoms and the overall clinical picture, rather than a single laboratory marker. [34]

In patients with indwelling catheters, the diagnostic value of dipsticks is even lower. Catheters are rapidly colonized by bacteria, so a positive dipstick or pyuria does not prove a catheter-associated infection. Guidelines specifically state that if such an infection is suspected, symptoms should be used as a guideline, and urine culture should be used to confirm and tailor therapy, rather than relying on dipstick testing to make a diagnosis. [35]

Finally, in young, sexually active patients with sterile pyuria without the typical presentation of cystitis, sexually transmitted infections should be considered. In the presence of risk factors or clinical indications, a standard urological diagnostic template may be insufficient, and then specific tests for chlamydial and gonococcal infections become more important. [36]

Prevention and prognosis

The prognosis depends not on the presence of leukocyturia itself, but on its cause. If it is associated with an episode of uncomplicated lower urinary tract infection, the outcome is usually favorable. If it is caused by pyelonephritis, obstruction, a stone, interstitial nephritis, tuberculosis, or a systemic disease, the timeliness and accuracy of diagnosis are crucial. Therefore, recurring or persistent leukocyturia should never be reassured simply because "this has happened before." [37]

Prevention begins with rational behavior, not prophylactic antibiotics. For some patients, adequate fluid intake, regular bladder emptying, prompt treatment of urological disorders, and reducing the risk of catheterization are helpful. But equally important is preventing diagnostic errors: avoiding incorrect urine collection, not interpreting asymptomatic urine dipsticks, and not blindly treating incidental laboratory findings. [38]

In pregnant women, prevention is primarily associated with timely urine culture screening early in pregnancy and treatment of confirmed asymptomatic bacteriuria. In children, it involves proper urine collection and rapid confirmation of the diagnosis if infection is suspected. In the elderly, it involves avoiding automatic antibiotic therapy based on a single test. In patients with a catheter, it involves minimizing the duration of catheterization and clinically justified use of cultures. [39]

One of the most useful preventative steps remains a competent interpretation of the test. A positive leukocyte esterase or an elevated white blood cell count in the urine is a reason to ask the next correct question, not to conclude the diagnosis. If there are no symptoms, a clinical context is needed. If the culture is negative, a search for sterile pyuria is necessary. If the patient belongs to a special group, standard guidelines should be adapted. This approach reduces both the risk of missing a serious illness and the risk of unnecessary antibiotics. [40]

FAQ

Do leukocytes in urine always indicate cystitis?
No. They are simply a marker of inflammation. The most common cause is indeed a urinary tract infection, but leukocytes can also be found in sterile pyuria, stones, catheters, interstitial nephritis, sexually transmitted infections, systemic diseases, and sample contamination. [41]

Can a dipstick test be used to make a diagnosis?
No. The dipstick is convenient for screening, but does not replace clinical evaluation. A positive leukocyte esterase or nitrite test increases the likelihood of infection, but specificity is limited in pregnant women, the elderly, and in contaminated samples. [42]

If leukocytes are present but the culture is negative, what does this mean?
This could be sterile pyuria. In this situation, consideration is given to a sample collection error, recent antibiotic use, sexually transmitted infections, urogenital tuberculosis, stones, drug-induced interstitial nephritis, and other non-infectious causes. [43]

Should leukocytes in urine be treated without symptoms?
Usually not. Asymptomatic bacteriuria is not treated in most cases, even if pyuria is present. The main exceptions are pregnancy and upcoming urological procedures that involve mucosal damage. [44]

Why does an elderly person have a negative urine test result, even though there may be no infection?
Because asymptomatic bacteriuria is common in older adults, and positive urine parameters are less effective in distinguishing between colonization and true infection. Therefore, for people over 65, diagnosis should be based primarily on symptoms and clinical presentation. [45]

Can a child's urine test be trusted if it was collected in a urine bag?
For culture, no. Bag-type urine collections in children carry a high risk of false-positive results and are only suitable as a preliminary screening option, not for confirming infection by culture. [46]

What should you do if leukocytes in your urine recur?
It's not just a retest that's needed, but proper routing: check the collection technique, compare it with your complaints, consider culture, and, if pyuria is sterile, consider additional testing for sexually transmitted infections, tuberculosis, stones, and drug-related and systemic causes. [47]

Is a urine culture necessary for everyone?
Not for everyone, but it is especially important in cases of pyelonephritis, pregnancy, children, men, patients with a catheter, atypical cases, relapses, and when symptoms differ from those found in a general urine analysis. [48]