What does the presence of blood and leukocytes (white blood cells) in a urinalysis (UA) indicate?

Blood and Leukocytes in Urinalysis: Clinical Significance

The presence of blood and leukocytes in a urinalysis indicates inflammation or infection in the urinary tract, but requires clinical correlation with symptoms to determine if treatment is warranted—never treat based on urinalysis findings alone. 1

Diagnostic Interpretation

The combination of leukocytes (detected by leukocyte esterase) and blood in urine has important diagnostic implications:

• Leukocytes (pyuria) combined with specific urinary symptoms (dysuria, frequency, urgency, fever, or gross hematuria) strongly suggests a urinary tract infection (UTI) and warrants further evaluation 1

• Leukocyte esterase has moderate sensitivity (83%) but limited specificity (78%) for detecting UTI, meaning positive results require clinical context before acting 1, 2

• When leukocyte esterase is combined with positive nitrite testing, specificity increases to 96% with combined sensitivity of 93%, making this combination highly predictive of true infection 1

• Blood (hematuria) in combination with leukocytes may indicate UTI, but can also suggest other conditions including kidney stones, glomerulonephritis, or genitourinary malignancy requiring different evaluation 3

Critical Decision Algorithm

Step 1: Assess for Symptoms

• If the patient has NO specific urinary symptoms (no dysuria, frequency, urgency, fever, or gross hematuria), do NOT pursue further UTI testing or treatment—this represents asymptomatic bacteriuria or contamination 1, 3

• If specific urinary symptoms ARE present, proceed to Step 2 1

Step 2: Evaluate Specimen Quality

• Check for epithelial cells on microscopy—high counts indicate contamination and false-positive leukocyte esterase results 1

• If contamination is suspected, obtain a proper specimen via midstream clean-catch or catheterization before making treatment decisions 1

Step 3: Determine Need for Culture

• Obtain urine culture if: Pyuria (≥10 WBCs/high-power field OR positive leukocyte esterase) AND acute onset of UTI-associated symptoms are present 1

• Always obtain culture before antibiotics in febrile infants under 2 years, suspected pyelonephritis, or immunocompromised patients 1

Step 4: Treatment Decision

• For symptomatic uncomplicated cystitis in healthy nonpregnant adults with positive leukocyte esterase and typical symptoms, empiric treatment without culture is acceptable 1

• For complicated UTI, pyelonephritis, or special populations, always obtain culture for antimicrobial susceptibility testing before starting antibiotics 1, 4

Special Population Considerations

Elderly and Long-Term Care Residents

• Asymptomatic bacteriuria with pyuria is extremely common (prevalence 15-50% in non-catheterized long-term care residents) and should NOT be treated 1

• Non-specific symptoms like confusion or functional decline alone should NOT trigger UTI treatment without specific urinary symptoms 1

• Evaluate only with acute onset of specific symptoms: fever, dysuria, gross hematuria, new/worsening urinary incontinence, or suspected bacteremia 1

Pediatric Patients

• In febrile infants and children (2 months to 2 years), always obtain both urinalysis and culture before antibiotics, as 10-50% of culture-proven UTIs have false-negative urinalysis 1

• Pyuria may be absent in UTIs caused by Klebsiella species and Enterococcus species, so absence of leukocytes does not exclude UTI in symptomatic children 5

• Use catheterization or suprapubic aspiration for specimen collection in young children to avoid contamination 1

Catheterized Patients

• Do NOT screen for or treat asymptomatic bacteriuria in patients with short-term or long-term indwelling catheters 1

• Reserve testing for symptomatic patients with fever, hypotension, or specific urinary symptoms 1

Common Pitfalls and How to Avoid Them

Pitfall 1: Treating Asymptomatic Findings

• Never treat based on urinalysis alone—the positive predictive value of pyuria for infection is exceedingly low without symptoms 1

• Asymptomatic bacteriuria with pyuria provides no clinical benefit when treated and leads to unnecessary antibiotic exposure and resistance development 1

Pitfall 2: Misinterpreting Contaminated Specimens

• Contamination is the most common cause of false-positive results—always assess specimen quality before acting 1

• If strong clinical suspicion exists despite poor specimen quality, obtain a properly collected specimen via catheterization rather than treating empirically 1

Pitfall 3: Ignoring Negative Predictive Value

• The absence of pyuria (negative leukocyte esterase AND no microscopic WBCs) has excellent negative predictive value (82-91%) for ruling out UTI in most populations 1

• Combined negative leukocyte esterase and nitrite effectively rules out UTI with 90.5% negative predictive value 1

Pitfall 4: Overlooking Non-Infectious Causes

• Sterile pyuria (leukocytes without positive culture) requires evaluation for non-infectious causes including interstitial nephritis, kidney stones, tuberculosis, or genitourinary malignancy 1

• Recurrent episodes of sterile pyuria require imaging (renal/bladder ultrasound) to evaluate for anatomic abnormalities 1

Key Limitations of Urinalysis Testing

• Leukocyte esterase sensitivity is lower in infants who void frequently, as shorter bladder dwell time results in fewer detectable leukocytes 1

• False-positive leukocyte esterase results occur with contaminated specimens, certain oxidizing agents, and some medications 1

• False-negative results may occur with high urinary glucose, high specific gravity, or certain antibiotics 1

• The test distinguishes true UTI from asymptomatic bacteriuria, as leukocyte esterase is typically absent in asymptomatic colonization 1