Diagnosis and Treatment of Urinalysis Positive for Nitrites and Leukocyte Esterase
A urinalysis positive for both nitrites and leukocyte esterase strongly indicates a urinary tract infection (UTI) requiring antibiotic treatment, with a combined specificity of 96% and sensitivity of 93%. 1, 2
Diagnostic Significance
- The combination of positive nitrites and leukocyte esterase has excellent diagnostic value, with nitrites having high specificity (98%) and leukocyte esterase having good sensitivity (83%) 1
- When both tests are positive, the likelihood of a true UTI is very high, as this combination achieves 96% specificity 2
- While a positive result strongly suggests UTI, definitive diagnosis requires urine culture with ≥50,000 CFU/mL of a uropathogen 1
- The presence of both markers indicates active infection rather than colonization or contamination 3
Treatment Approach
First-line Empiric Therapy:
- For uncomplicated UTI in adults, oral fluoroquinolones are effective first-line outpatient treatment 4
- Alternative effective options include:
- Extended-spectrum penicillins
- Amoxicillin-clavulanate potassium
- Cephalosporins
- Trimethoprim-sulfamethoxazole 4
Duration of Therapy:
- Standard treatment duration is 7-14 days for most UTIs 4
- Uncomplicated cystitis in women may be treated with shorter courses (3-5 days) 4
Special Populations
Children:
- In children with suspected UTI, urine culture should be obtained before starting antibiotics, even with positive dipstick results 5
- Ceftriaxone (75 mg/kg/day) is recommended for initial parenteral therapy in children 3
- For oral therapy in children, cefixime (8 mg/kg/day) or amoxicillin/clavulanic acid (20-40 mg/kg/day in 3 doses) are appropriate options 3
Hospitalization Criteria:
- Indications for inpatient treatment include:
- Complicated infections
- Sepsis
- Persistent vomiting
- Failed outpatient treatment
- Extremes of age 4
- For hospitalized patients, intravenous therapy with a fluoroquinolone, aminoglycoside (with or without ampicillin), or third-generation cephalosporin is recommended 4
Follow-up and Monitoring
- Urine culture should be repeated 1-2 weeks after completion of antibiotic therapy to confirm resolution 4
- If symptoms persist despite appropriate therapy, consider:
- Resistant organisms
- Underlying anatomical abnormalities
- Immunosuppression 4
- Lack of response should prompt repeat cultures and possible imaging studies 4
Common Pitfalls to Avoid
- Do not rule out UTI based solely on negative nitrite results, as this would miss many true infections (nitrites have only 53% sensitivity) 1
- Do not diagnose UTI based on positive culture alone without evidence of pyuria, as this may represent asymptomatic bacteriuria 1
- Be aware that pyuria might be lacking in UTIs caused by certain pathogens like Klebsiella spp. and Enterococcus spp. 6
- Avoid nitrofurantoin for febrile UTIs as it does not achieve therapeutic concentrations in the bloodstream 3
- Remember that urine specimens must be processed within 1 hour at room temperature (or 4 hours if refrigerated) to ensure accurate results 1
Pathogen Considerations
- E. coli is the most common uropathogen (approximately 80% of cases) 6, 4
- E. coli infections more commonly cause leukocyturia and pyuria compared to other pathogens 6
- Klebsiella and Enterococcus infections may present with less pronounced pyuria 6
- Antibiotic resistance patterns vary by pathogen, with high ampicillin resistance noted in Klebsiella (100%) and E. coli (72%) 6