What is the term for the presence of White Blood Cells (WBCs) in urinalysis?

Pyuria: The Term for White Blood Cells in Urinalysis

The term for the presence of white blood cells (WBCs) in urinalysis is "pyuria." Pyuria is defined as an abnormal number of white blood cells in the urine, typically ≥10 WBCs per high-power field (HPF) in centrifuged urine specimens or ≥10 WBCs/mm³ in uncentrifuged urine 1.

Clinical Significance of Pyuria

Pyuria is a key indicator in the diagnostic evaluation of urinary tract infections (UTIs). Its presence suggests inflammation in the urinary tract, which is often, but not always, associated with infection.

Diagnostic Thresholds

• Standard definition: ≥10 WBCs/HPF in centrifuged urine or ≥10 WBCs/mm³ in uncentrifuged urine 1
• Enhanced urinalysis: Using a hemocytometer count of uncentrifuged urine with a threshold of ≥10 WBCs/mm³ 2
• Higher threshold: Some recent research suggests that >25 WBCs/HPF may be a more optimal cutoff for predicting bacteriuria 3

Detection Methods

1. Microscopic examination: Direct visualization of WBCs in urine sediment
2. Dipstick leukocyte esterase test: Indirect detection of WBCs through enzymatic activity
3. Automated urinalysis: Flow imaging analysis technology that classifies particles in uncentrifuged urine 1

Clinical Interpretation

Diagnostic Performance

• Sensitivity: 83% (67-94%) for leukocyte esterase test 1
• Specificity: 78% (64-92%) for leukocyte esterase test 1
• Negative predictive value: Approaches 100% - the absence of pyuria can effectively exclude bacteriuria in most cases 1

Important Clinical Considerations

• Pyuria without bacteriuria may occur in:

  • Chemical irritation of the urinary tract
  • Kidney stones
  • Interstitial nephritis
  • Certain medications
  • Sterile inflammatory conditions

• Bacteriuria without pyuria may occur in:

  • Asymptomatic bacteriuria 1
  • Neutropenic patients 1
  • Early stages of UTI 2

Special Populations

Elderly Patients

In long-term care facility residents, pyuria alone has a relatively low positive predictive value for UTI but high negative predictive value. Guidelines recommend that:

• Urinalysis and urine cultures should not be performed for asymptomatic residents 1
• Diagnostic evaluation should be reserved for those with acute onset of UTI-associated symptoms 1
• Minimum laboratory evaluation should include urinalysis for leukocyte esterase, nitrite, and microscopic examination for WBCs 1

Pediatric Patients

In children, the diagnostic criteria for pyuria are similar:

• Pyuria defined as ≥10 WBCs/HPF or positive leukocyte esterase 1
• For diagnosis of UTI, both pyuria and bacteriuria should be present, along with ≥50,000 CFUs/mL of a uropathogen 1

Common Pitfalls

1. Overreliance on pyuria: While pyuria is a sensitive marker for UTI, it is not specific enough to diagnose UTI on its own 3

2. Ignoring the absence of pyuria: The absence of pyuria has excellent negative predictive value and can effectively rule out UTI in most cases 1

3. Treating asymptomatic bacteriuria: The presence of bacteria without symptoms or pyuria generally does not require treatment, especially in elderly patients 1

4. Collection method issues: Contamination rates vary significantly by collection method:

   • Suprapubic aspiration: 1%
   • Catheterization: 12%
   • Clean catch: 26% 1

In summary, pyuria is a valuable diagnostic marker in urinalysis that indicates inflammation in the urinary tract. While its presence alone is not sufficient to diagnose UTI, its absence is a strong indicator against active infection in most clinical scenarios.