What does the urinalysis indicate?

Urinalysis Interpretation and Clinical Action

What the Urinalysis Indicates

The urinalysis findings determine whether a urinary tract infection (UTI) is present and whether treatment is warranted, but the results must always be interpreted alongside clinical symptoms—never in isolation. 1

Core Diagnostic Principles

• Both pyuria (≥10 WBCs/high-power field or positive leukocyte esterase) AND acute urinary symptoms (dysuria, frequency, urgency, fever >38.3°C, or gross hematuria) are required to diagnose and treat a UTI. 1

• A positive urinalysis alone—without symptoms—represents asymptomatic bacteriuria in 15–50% of older adults and should never be treated. 1

• The absence of both leukocyte esterase and nitrite effectively rules out UTI with 90.5% negative predictive value, making bacterial infection extremely unlikely. 1

Interpreting Specific Urinalysis Components

Leukocyte Esterase

• Positive leukocyte esterase indicates pyuria with 83% sensitivity and 78% specificity for UTI. 2, 3
• When combined with nitrite testing, sensitivity increases to 93% with 72% specificity. 1, 2
• Absence of leukocyte esterase has excellent negative predictive value (82–91%) for ruling out infection. 1

Nitrite Test

• Positive nitrite is highly specific (98–100%) for gram-negative bacteria but has poor sensitivity (19–53%). 1, 3
• A negative nitrite does NOT rule out UTI, especially in patients who void frequently (shorter bladder dwell time prevents nitrite conversion). 4, 1

Microscopic Findings

• Pyuria threshold: ≥10 WBCs/high-power field correlates with significant bacteriuria when symptoms are present. 1, 2
• Bacteriuria on microscopy has 81% sensitivity and 83% specificity for culture-positive UTI. 3
• High epithelial cell counts indicate contamination; repeat collection via catheterization is required. 4, 1

Clinical Decision Algorithm

Step 1: Assess for Specific Urinary Symptoms

• Required symptoms: dysuria, urinary frequency, urgency, fever >38.3°C, gross hematuria, or suprapubic pain 1
• If NO symptoms are present: Do not order culture or treat—this represents asymptomatic bacteriuria 1
• Non-specific symptoms in elderly (confusion, falls, weakness) do NOT justify UTI testing without urinary symptoms. 1

Step 2: Verify Pyuria

• If leukocyte esterase is positive OR microscopy shows ≥10 WBCs/HPF: Proceed to urine culture before starting antibiotics 1, 2
• If both leukocyte esterase and nitrite are negative: UTI is ruled out; search for alternative diagnoses 1

Step 3: Obtain Urine Culture When Indicated

• Culture is mandatory when: pyuria + symptoms are present, or in febrile infants <2 years (10–50% have false-negative urinalysis) 4, 1
• Culture thresholds: ≥50,000 CFU/mL in children, ≥100,000 CFU/mL in adults for clean-catch specimens 1, 2

Step 4: Initiate Treatment Only When Both Criteria Are Met

• Pyuria (≥10 WBCs/HPF or positive leukocyte esterase) + acute urinary symptoms = treat empirically while awaiting culture 1, 2
• First-line therapy: Nitrofurantoin 100 mg PO BID for 5–7 days (resistance <5%) 1
• Alternatives: Fosfomycin 3 g single dose or trimethoprim-sulfamethoxazole 160/800 mg BID for 3 days (only if local resistance <20%) 1

Special Population Considerations

Elderly and Long-Term Care Residents

• Asymptomatic bacteriuria prevalence: 15–50%; pyuria has low predictive value in this population. 1
• Test only when acute urinary symptoms + systemic signs (fever, rigors, delirium, hypotension) are present. 1
• Cloudy or foul-smelling urine alone does NOT indicate infection and should not trigger testing. 1

Catheterized Patients

• Bacteriuria and pyuria are nearly universal (≈100%) in long-term catheterization; do not screen or treat asymptomatic findings. 1
• Test only when fever, hypotension, rigors, or suspected urosepsis are present; replace catheter before specimen collection. 1

Pediatric Patients (<2 Years)

• Always obtain both urinalysis and culture before antibiotics; 10–50% of culture-proven UTIs have false-negative urinalysis. 4, 1
• Preferred collection methods: catheterization or suprapubic aspiration (bag specimens have 85% false-positive rate). 4, 2

Critical Pitfalls to Avoid

• Never treat based on urinalysis alone without confirming symptoms—this promotes resistance and causes harm. 1
• Never assume negative nitrite rules out UTI; sensitivity is only 19–53%. 1, 3
• Never treat asymptomatic bacteriuria (except in pregnancy or before urologic procedures with mucosal bleeding). 1
• Never delay culture collection when treatment is indicated; obtain culture before starting antibiotics. 1
• Never use bag-collected specimens for definitive diagnosis in children; confirm positive results with catheterization. 4, 2

When Urinalysis Results Are Equivocal

• If symptoms are present but urinalysis is negative: Consider early infection (bacteria present before inflammatory response develops) or non-infectious causes 1
• If urinalysis is positive but symptoms are absent: This is asymptomatic bacteriuria—do not treat 1
• If specimen shows contamination (mixed flora, high epithelial cells): Recollect via catheterization before making treatment decisions 4, 1