Will white blood cell (WBC) count be elevated in a patient with a urinary tract infection (UTI)?

White Blood Cell Elevation in Urinary Tract Infections

Yes, white blood cell (WBC) count is typically elevated in patients with urinary tract infections, with leukocytosis (>14,000 cells/mm³) having a likelihood ratio of 3.7 for detecting bacterial infection. 1, 2

Systemic WBC Response in UTIs

The presence of a UTI often triggers an inflammatory response that can be detected in the bloodstream:

• Leukocytosis (WBC >14,000 cells/mm³) indicates a high probability of bacterial infection 1
• Left shift (increased band neutrophils) provides even stronger evidence of infection:
  • Band counts >1,500 cells/mm³: likelihood ratio 14.5
  • Neutrophils >90%: likelihood ratio 7.5
  • Band neutrophils >16%: likelihood ratio 4.7 2

In elderly patients, an elevated WBC count with or without fever, high percentage of neutrophils, or left shift (even with normal total leukocyte count) strongly suggests an underlying bacterial infection. 1

Local WBC Response in Urine

UTIs also produce a local inflammatory response with increased WBCs in the urine:

• Normal uninfected urine typically contains ≤10³ WBCs/mL
• Infected urine regularly contains >10⁴ WBCs/mL, with mean counts of 3.1×10⁵ WBCs/mL 3
• The absence of pyuria provides strong evidence against UTI 3
• A cutoff of 40 WBCs/μL in urine is recommended for screening for UTI 4

Diagnostic Approach for UTI

When evaluating for UTI, the following approach is recommended:

1. Urinalysis first:

   • Look for pyuria (≥10 WBCs/high-power field)
   • Check for positive leukocyte esterase or nitrite test on dipstick 1
   • WBC in urine has sensitivity of 62.7% and specificity of 100% for UTI 5

2. Proceed to urine culture only if pyuria is present 1

3. Blood tests when appropriate:

   • Complete blood count with differential if systemic infection is suspected
   • Blood cultures if urosepsis is suspected 1

Important Clinical Considerations

• WBC elevation may not be present in all UTI cases, particularly in immunocompromised patients
• Elderly patients may present with atypical symptoms and signs of UTI (confusion, incontinence, anorexia, functional decline) 1
• Asymptomatic bacteriuria (positive urinalysis without symptoms) is common in older adults and should not be treated with antibiotics 6
• The combination of clinical symptoms plus laboratory findings provides the most accurate diagnosis 2

Common Pitfalls to Avoid

• Do not rely solely on WBC count for diagnosis; clinical symptoms must be present
• Do not perform urinalysis or urine cultures for asymptomatic patients 1
• Do not assume that bacteriuria in catheterized patients indicates infection; look for signs of urosepsis 1
• Do not overlook the importance of proper specimen collection, which may require special techniques in elderly or functionally impaired patients 1