What are the typical urinalysis findings in a urinary tract infection (UTI)?

Typical Urinalysis Findings in Urinary Tract Infection (UTI)

The diagnosis of UTI requires both positive urinalysis findings (leukocyte esterase, pyuria, or nitrites) AND clinical symptoms of infection, with the combination of leukocyte esterase and nitrite providing high diagnostic accuracy with a sensitivity of 93% and specificity of 72%. 1

Key Urinalysis Findings in UTI

Leukocyte Esterase and Nitrite Tests

• Leukocyte esterase: Sensitivity 83% (67-94%), specificity 78% (64-92%) 1
• Nitrite: Sensitivity 53% (15-82%), specificity 98% (90-100%) 1
• Combined (leukocyte esterase OR nitrite): Sensitivity 93% (90-100%), specificity 72% (58-91%) 1
• When used individually, neither test is reliable enough to rule out UTI 2

Microscopic Examination

• Pyuria (WBCs in urine):
  • WBC count >100/μL: 93% sensitivity, 71% specificity 1
  • WBC count >200/μL: 89% sensitivity, 86% specificity 1
  • Traditional threshold: ≥5 WBCs/hpf 3
• Bacteria on microscopy:
  • Unstained bacteria: 88% sensitivity, 92% specificity 3
  • Gram-stained bacteria: 91% sensitivity, 96% specificity 3

Diagnostic Performance of Urinalysis

A meta-analysis of 95 studies in 95,703 children found that rapid diagnostic tests were negative in about 10% of children with confirmed UTIs, indicating that urinalysis cannot completely replace urine culture 3.

When examining individual components:

• Blood alone had the highest sensitivity for a single screening test at 63.94% 2
• The presence of leukocyte esterase and/or blood increased sensitivity to 72.28% 2
• The highest sensitivity was achieved when nitrite, leukocyte esterase, and blood were considered together 2

Clinical Implications

1. Confirmation with Culture: True infection requiring treatment is typically diagnosed by a positive urine culture (≥50,000 CFU/mL of a uropathogen) plus symptoms 1

2. Organism Prediction: A positive urinalysis is more likely to be associated with E. coli infection (82.1%), while negative urinalysis with positive culture often indicates non-E. coli organisms (59%) 4

3. Collection Method Matters: Contamination rates vary significantly by collection method:

   • Suprapubic aspiration: 1% contamination
   • Catheter specimen: 12% contamination
   • Clean catch: 26% contamination 3

Common Pitfalls to Avoid

1. Relying solely on WBC count: High WBC counts must be interpreted with clinical symptoms 1

2. Ignoring symptoms with lower colony counts: Lower CFU counts can still indicate significant infections in symptomatic patients 1

3. Treating asymptomatic bacteriuria: Asymptomatic bacteriuria is common (10-50%) and should generally not be treated except in specific populations like pregnant women 1

4. Misinterpreting results in catheterized patients: Bacteriuria and pyuria are virtually universal in chronic catheterization and not necessarily indicative of infection 1

5. Assuming negative dipstick rules out UTI: Symptomatic patients with negative dipstick assay should still undergo urine culture if clinical suspicion is high 2

By combining urinalysis findings with clinical symptoms, clinicians can make more accurate diagnoses of UTI and avoid unnecessary antibiotic use or missed infections.