What does it mean if I have leukocytes (white blood cells) in my urine?

Leukocytes in Urine: Clinical Significance and Evaluation

Leukocytes (white blood cells) in your urine typically indicate inflammation in the urinary tract, most commonly due to a urinary tract infection (UTI), though other non-infectious causes should be considered if bacteriuria is absent. 1

Understanding Leukocytes in Urine

• Leukocytes in urine (pyuria) are most commonly associated with urinary tract infections when accompanied by bacteriuria 1
• Leukocyte esterase is an enzyme released from white blood cells that can be detected through dipstick testing, with results typically reported as negative, trace, 1+, 2+, or 3+ based on color intensity 2
• The presence of leukocytes alone is not diagnostic of infection and requires clinical correlation with symptoms and potentially urine culture 3
• Leukocyte esterase testing has moderate sensitivity (83%, range 67-94%) but limited specificity (78%, range 64-92%) for detecting UTIs 2

Clinical Significance

When Leukocytes Suggest Infection:

• Leukocytes combined with symptoms such as dysuria, frequency, urgency, fever, or gross hematuria strongly suggest a UTI 3, 4
• When leukocytes are accompanied by a positive nitrite test, the specificity for UTI increases to 96% (combined sensitivity 93%) 4, 2
• The absence of pyuria (negative leukocyte esterase and no microscopic WBCs) has excellent negative predictive value for ruling out UTI 4, 2

When Leukocytes May Not Indicate Infection:

• Asymptomatic bacteriuria with pyuria is common, especially in older adults (prevalence 15-50% in non-catheterized long-term care facility residents) 4
• In catheterized patients, both bacteriuria and pyuria are nearly universal and do not necessarily indicate infection requiring treatment 4, 3
• Sterile pyuria (leukocytes without significant bacteriuria) requires further diagnostic evaluation 1

Diagnostic Approach

Initial Assessment:

• Determine if symptoms consistent with UTI are present (dysuria, frequency, urgency, fever, gross hematuria) 3, 4
• Consider both leukocyte esterase and nitrite testing, as the combination improves diagnostic accuracy 4, 2
• Microscopic examination for WBCs is recommended when leukocyte esterase is positive 4

When to Culture:

• If pyuria (≥10 WBCs/high-power field or positive leukocyte esterase) is present AND symptoms suggest UTI, a urine culture should be obtained 4, 3
• In asymptomatic individuals, urinalysis and urine cultures should not be performed routinely 4
• For suspected urosepsis, both urine and blood cultures should be collected 4

Special Considerations

In Older Adults:

• Non-specific symptoms like confusion or functional decline alone should not trigger UTI treatment without specific urinary symptoms 4, 3
• The minimum laboratory evaluation for suspected UTI should include urinalysis for leukocyte esterase, nitrite, and microscopic examination for WBCs 4
• In long-term care facilities, evaluation is indicated only with acute onset of UTI-associated symptoms 4

In Children:

• In febrile infants and young children, positive leukocyte esterase should prompt urine culture collection before initiating antimicrobial therapy 4, 2
• The test has lower sensitivity in infants who void frequently due to shorter bladder dwell time 2

Potential Causes of False Results

• False-positive leukocyte esterase results can occur with contaminated specimens, certain oxidizing agents, and some medications 2
• False-negative results may occur with high urinary glucose, high specific gravity, or certain antibiotics 2
• Proper specimen collection is essential to avoid contamination that can lead to misleading results 4

Monitoring Response to Treatment

• During antibiotic treatment for UTI, leukocyte counts typically show the deepest decrease within the first 24 hours 5
• Persistent or increasing leukocyte counts during treatment may indicate treatment failure 5