What is the likely diagnosis and treatment for a urinalysis showing presence of nitrites and leukocytes, indicating a potential urinary tract infection (UTI)?

Interpreting Urinalysis with Nitrites and Leukocytes

When both nitrites AND leukocyte esterase are positive on urinalysis, this combination has 96% specificity and 93% sensitivity for UTI—making it one of the most reliable dipstick combinations that justifies immediate empiric antibiotic treatment in symptomatic patients while awaiting culture results. 1

Diagnostic Performance of Individual Components

Nitrite Testing

• Nitrite positivity has 98% specificity but only 53% sensitivity for UTI 1
• A positive nitrite strongly indicates infection, but a negative result does NOT rule it out 1, 2
• Nitrite requires approximately 4 hours of bladder dwell time to convert dietary nitrates to nitrites, explaining poor sensitivity in patients who void frequently 1
• In elderly patients specifically, nitrites are likely more sensitive and specific than other dipstick components 2

Leukocyte Esterase Testing

• Leukocyte esterase alone has 83% sensitivity and 78% specificity 1, 3
• The absence of leukocyte esterase combined with negative nitrite has excellent negative predictive value (82-91%) for ruling out UTI 3
• Leukocyte esterase helps distinguish true UTI from asymptomatic bacteriuria, as it is typically absent in colonization 3

Combined Testing

• When either leukocyte esterase OR nitrite is positive, sensitivity increases to 93% with 72% specificity 3
• When BOTH are negative, UTI is effectively ruled out in most populations (<0.3% probability) 4
• The combination of both positive achieves the highest specificity at 96% 1

Mandatory Next Steps After Positive Results

Obtain Urine Culture Before Treatment

• Urine culture must be obtained before initiating antibiotics—urinalysis cannot substitute for culture to document UTI 1
• Culture results guide definitive antibiotic therapy and detect resistance patterns 1
• The American Academy of Pediatrics requires both urinalysis suggesting infection AND positive culture with ≥50,000 CFU/mL for definitive UTI diagnosis 4

Assess for Clinical Symptoms

• The presence of symptoms is the key distinguishing feature between true UTI and asymptomatic bacteriuria 1, 3
• Required symptoms include: dysuria, frequency, urgency, fever, or gross hematuria 1, 3
• Positive dipstick without symptoms represents asymptomatic bacteriuria, which should NOT be treated 1, 3

Treatment Algorithm Based on Results

Both Nitrite AND Leukocyte Esterase Positive + Symptoms Present

• Start empiric antibiotics immediately after obtaining urine culture 1
• The 96% specificity of this combination justifies empiric treatment while awaiting culture 1
• First-line antibiotics: nitrofurantoin, fosfomycin, or trimethoprim-sulfamethoxazole (when local resistance <20%) 5, 2
• Short-course therapy of 3-5 days is recommended for uncomplicated UTIs 1

Either Test Positive + Symptoms Present

• Obtain urine culture before treatment 1
• Consider empiric treatment based on clinical judgment and symptom severity 3
• The 93% sensitivity of either test positive supports treatment in symptomatic patients 3

Both Tests Negative + Symptoms Present

• UTI is unlikely but not completely ruled out 4
• In patients with high pretest probability based on symptoms, negative dipstick does NOT rule out UTI 2
• Consider urine culture if clinical suspicion remains high 3
• Interestingly, trimethoprim treatment significantly reduced dysuria even in dipstick-negative symptomatic women (median resolution 3 days vs 5 days placebo, number needed to treat = 4) 6

Positive Tests WITHOUT Symptoms

• Do NOT treat—this represents asymptomatic bacteriuria 1, 3
• Asymptomatic bacteriuria prevalence is 15-50% in long-term care residents 1
• Treatment of asymptomatic bacteriuria causes more harm than good by promoting antibiotic resistance 1

Special Population Considerations

Elderly and Frail Patients

• The specificity of urine dipstick tests ranges from only 20-70% in elderly patients 7
• Negative results for both nitrite AND leukocyte esterase often suggest absence of UTI 7
• Non-specific symptoms (confusion, falls, functional decline) alone should NOT trigger UTI treatment without specific urinary symptoms 7, 3
• Prescribe antibiotics ONLY when recent onset dysuria, frequency, urgency, or costovertebral angle tenderness is present—UNLESS urinalysis shows negative nitrite AND negative leukocyte esterase 7

Febrile Infants and Young Children

• Obtain urine culture regardless of urinalysis results, as 10-50% of culture-proven UTIs have false-negative urinalysis 1
• Young infants have particularly poor nitrite sensitivity due to frequent voiding and short bladder dwell time 1
• Pyuria is absent in approximately 20% of febrile infants with culture-proven pyelonephritis 4

Catheterized Patients

• Initiate empiric antibiotics ONLY if symptomatic (fever, hemodynamic instability) 1
• Change the catheter before collecting the culture specimen 1
• Do NOT screen for or treat asymptomatic bacteriuria in catheterized patients 3

Critical Pitfalls to Avoid

Specimen Collection Errors

• Bagged urine specimens have 85% false-positive rates when positive 1
• Always confirm positive bagged specimens with catheterized specimen before treating 1
• For women requiring definitive specimen: perform in-and-out catheterization 3
• For cooperative men: use midstream clean-catch or freshly applied clean condom catheter 3

Interpretation Errors

• Do NOT rule out UTI based solely on negative nitrite results—this would miss many true infections 4, 2
• Do NOT diagnose UTI based on positive culture alone without evidence of pyuria—this may represent asymptomatic bacteriuria 4
• Pyuria is commonly found in the absence of infection, particularly in older adults with lower urinary tract symptoms such as incontinence 2

Treatment Errors

• Do NOT treat asymptomatic bacteriuria with pyuria—this is a strong recommendation against treatment 3
• In older adults with delirium, confusion, or falls alone without specific urinary symptoms, do NOT treat 3
• Urine specimens must be processed within 1 hour at room temperature or 4 hours if refrigerated to ensure accurate results 4