What urinalysis results indicate treatment for a urinary tract infection (UTI)?

Urinalysis Results That Indicate Treatment for UTI

Urinary tract infection (UTI) should be treated when there is both a positive urinalysis showing evidence of infection (pyuria and/or bacteriuria) AND a positive urine culture with at least 50,000 CFU/mL of a uropathogen from a properly collected specimen. 1

Diagnostic Criteria for UTI

Urinalysis Findings Suggestive of UTI:

• Pyuria: ≥10 WBCs/high-power field on microscopic examination 1
• Positive leukocyte esterase on dipstick testing 1
• Positive nitrite test on dipstick testing 1
• Microscopy positive for bacteria 1

Urine Culture Requirements:

• Growth of ≥50,000 CFU/mL of a uropathogen (previously the threshold was 100,000 CFU/mL) 1
• Specimen should be collected via catheterization or suprapubic aspiration for definitive diagnosis 1

Diagnostic Algorithm

Step 1: Evaluate Urinalysis Results

• If urinalysis shows positive leukocyte esterase OR positive nitrite OR microscopy positive for WBCs OR bacteria, proceed to urine culture 1
• If urinalysis of fresh urine (less than one hour since void) is negative for leukocyte esterase AND nitrites, UTI is unlikely (<0.3%) and can be followed clinically without antimicrobial therapy 1

Step 2: Confirm with Urine Culture

• Obtain urine culture via catheterization or suprapubic aspiration 1
• Pure growth of ≥50,000 CFU/mL of a uropathogen with urinalysis demonstrating bacteriuria or pyuria confirms UTI 1

Special Considerations

For Long-Term Care Facility Residents:

• In residents with chronic indwelling urinary catheters, bacteriuria and pyuria are virtually universal and not necessarily indicative of symptomatic infection 1
• For residents with suspected urosepsis, catheters should be changed prior to specimen collection and antibiotic therapy 1
• Minimum laboratory evaluation should include urinalysis for leukocyte esterase, nitrite, and microscopic examination for WBCs 1
• Only if pyuria (≥10 WBCs/high-power field) or positive leukocyte esterase or nitrite test is present should a urine culture be ordered 1

For Infants and Young Children:

• Both an abnormal urinalysis result AND a positive urine culture result are needed to confirm UTI 1
• Positive culture is defined as ≥50,000 CFU/mL 1
• Bag specimens are not reliable for culture due to high contamination rates; catheterization or suprapubic aspiration is required 1

Performance of Urinalysis Tests

Sensitivity and Specificity:

• Leukocyte esterase test: Sensitivity 83% (67-94%), Specificity 78% (64-92%) 1
• Nitrite test: Sensitivity 53% (15-82%), Specificity 98% (90-100%) 1
• Combined leukocyte esterase or nitrite positive: Sensitivity 93% (90-100%), Specificity 72% (58-91%) 1
• Microscopy for WBCs: Sensitivity 73% (32-100%), Specificity 81% (45-98%) 1
• Microscopy for bacteria: Sensitivity 81% (16-99%), Specificity 83% (11-100%) 1

Important Caveats:

• Nitrite test is not sensitive in patients who empty their bladders frequently (e.g., infants) 1
• Negative nitrite test results have little value in ruling out UTI, but positive results are highly specific 1
• Urine specimens must be fresh (processed within 1 hour at room temperature or 4 hours if refrigerated) 1
• Automated urinalysis provides more sensitive detection of leukocytes and bacteria than manual methods 2

Common Pitfalls to Avoid

• Do not treat asymptomatic bacteriuria in most populations, as it does not increase morbidity or mortality 1
• Do not rely solely on symptoms for diagnosis, as more pronounced symptoms do not correlate with significant bacteriuria 3
• Do not use bag urine specimens for culture due to high contamination rates (85% false positive rate with bagged specimens) 1
• Do not assume all positive cultures represent infection - distinguish UTI from asymptomatic bacteriuria, especially in catheterized patients 1
• Do not start antibiotics before obtaining urine specimens as most agents will sterilize the urine rapidly, obscuring diagnosis 1

Antibiotic Selection

• Treatment should be guided by local antibiotic susceptibility patterns 1
• Common antibiotics include trimethoprim-sulfamethoxazole for susceptible E. coli, Klebsiella, Enterobacter, Morganella morganii, and Proteus species 4
• Levofloxacin is indicated for complicated UTIs due to various pathogens including E. coli, Klebsiella pneumoniae, and Proteus mirabilis 5