Can sexually transmitted infections (STIs) cause a positive nitrite test in urine?

STIs and Urinary Nitrite Testing

Sexually transmitted infections (STIs) typically do not cause positive nitrite tests in urine, as nitrite positivity is primarily associated with urinary tract infections (UTIs) caused by enteric bacteria rather than STI pathogens.

Relationship Between STIs and Urinalysis Findings

Nitrite Test Mechanism

• Nitrite in urine is produced when bacteria convert dietary nitrates to nitrites
• This conversion requires approximately 4 hours of bacterial presence in the bladder 1
• Common enteric gram-negative bacteria (typical UTI pathogens) perform this conversion
• STI pathogens generally do not produce this conversion

STI Pathogens and Urinalysis

STI pathogens typically associated with urethritis include:

• Neisseria gonorrhoeae
• Chlamydia trachomatis
• Mycoplasma genitalium
• Trichomonas vaginalis
• Ureaplasma urealyticum 1

These organisms generally do not produce nitrite in urine, which explains why:

• STIs typically cause sterile pyuria (WBCs without nitrites) 2
• In a study of women with confirmed STIs, 74% of those with pyuria had sterile pyuria with negative urine cultures 2

Distinguishing STIs from UTIs in Urinalysis

Urinalysis Patterns

Different patterns in urinalysis can help distinguish between STIs and UTIs:

1. Positive nitrites or protein: 55% had UTI 3
2. Positive leukocytes or blood without nitrites: 62% had STI 3
3. Both nitrites/protein and leukocytes/blood positive: 28% had STI and 65% had UTI 3

Key Diagnostic Findings

• Nitrite test has high specificity (94-98%) for UTIs but low sensitivity for STIs 4, 1
• Leukocyte esterase positivity without nitrites is more suggestive of STI than UTI 3, 2
• 65% of patients with sterile pyuria (leukocytes without bacteria) had STIs, primarily trichomoniasis or gonorrhea 3

Clinical Implications

Diagnostic Approach

When evaluating patients with urinary symptoms:

• Do not rule out STI based on presence of urinary symptoms alone
• Test for both UTI and STI in sexually active patients with urinary symptoms 3
• Consider that STIs and UTIs can coexist in the same patient

Common Pitfalls

1. Misdiagnosis: Relying solely on urinalysis for diagnosis can lead to missed STIs

   • In one study, 66% of patients prescribed antibiotics for suspected UTI had negative urine cultures 2

2. Overtreatment: Treating presumed UTI in patients with STI

   • Substantial overtreatment occurs when empiric UTI treatment is given based on pyuria alone in patients with STIs 2

3. Missed Diagnosis: Failing to test for STIs in patients with urinary symptoms

   • Comprehensive testing should include both UTI and STI evaluation in sexually active patients 5

Special Considerations

High-Risk Populations

• More frequent STI screening (every 3-6 months) is recommended for patients with:
  • Multiple or anonymous partners
  • Previous STI diagnosis
  • Substance use
  • Unprotected sex outside monogamous relationships 5

Testing Recommendations

• NAAT testing is the gold standard for chlamydia and gonorrhea detection (sensitivity 86.1%-100%, specificity 97.1%-100%) 5
• Comprehensive STI screening should include testing for chlamydia, gonorrhea, trichomonas, syphilis, and HIV 5

In summary, while STIs typically do not cause positive nitrite tests, they frequently cause pyuria. The presence of leukocytes without nitrites in urine should raise suspicion for an STI rather than a UTI, especially in sexually active individuals.