Will a Urinalysis Show Leukocytes if the Infection is Sexually Transmitted?
Yes, a urinalysis will frequently show leukocytes (pyuria) in the presence of sexually transmitted infections, but this finding is highly misleading and often results in misdiagnosis and inappropriate antibiotic treatment for presumed UTI.
The Critical Problem: Sterile Pyuria in STIs
The presence of leukocytes in urine is common with STIs, but this represents sterile pyuria (white blood cells without bacterial growth on culture):
- In women with confirmed STIs (gonorrhea, chlamydia, or trichomoniasis), 37% had pyuria, and of those with pyuria, 74% had sterile pyuria with negative urine cultures 1
- This high prevalence of sterile pyuria leads to substantial overtreatment with UTI antibiotics when an STI is the actual diagnosis 1
- No association exists between having a positive STI test and having a urine culture yielding ≥10,000 CFU/mL of bacteria, meaning STIs and bacterial UTIs rarely occur together 2
Why Leukocytes Appear in STI Cases
Sexually transmitted pathogens cause urethritis and cervicitis, which produce inflammatory responses:
- Urethritis (from gonorrhea or chlamydia) is documented by ≥5 polymorphonuclear leukocytes per oil immersion field on urethral smear 3
- The leukocyte esterase test is specifically recommended by the CDC for screening urethritis in males, including detection of chlamydial and gonococcal infections 4
- In asymptomatic men at high risk for chlamydial infection, 86.9% of those positive for chlamydia had elevated urinary leukocytes (median 43.3 WBCs/μL) 5
The Diagnostic Trap and How to Avoid It
Common Pitfall:
Emergency departments routinely misdiagnose STIs as UTIs based on pyuria alone:
- In one study, 66% of women diagnosed with UTI were treated without urine culture, and only 48% actually had positive cultures 6
- Of 60 women with positive STI tests, 37% did not receive STI treatment within 7 days, and 64% of these were misdiagnosed with UTI instead 6
- When UTI antibiotics were prescribed in the setting of confirmed STIs, 66% had negative urine cultures, representing inappropriate treatment 1
The Correct Diagnostic Approach:
Step 1: Assess Clinical Context
- Consider STI risk factors: new or multiple partners, age <25 years, inconsistent condom use, partner with STI 3
- Distinguish urethritis/cervicitis symptoms (mucopurulent discharge, dysuria) from typical UTI symptoms 3
Step 2: Interpret Urinalysis Correctly
- Pyuria alone has exceedingly low positive predictive value for UTI and often indicates genitourinary inflammation from noninfectious causes 4
- The combination of leukocyte esterase OR nitrite has 93% sensitivity but only 72% specificity for UTI 4, 7
- Nitrite-positive urines in STI cases were actually 18% more likely to be associated with negative urine cultures 1
Step 3: Test for Both Conditions When Indicated
- All patients with urethritis should be evaluated for both gonorrhea and chlamydia using nucleic acid amplification tests 3
- Obtain urine culture only if pyuria is present AND specific urinary symptoms suggest true UTI (fever, urgency, frequency, gross hematuria) 4
- Do not treat for UTI based on pyuria alone in patients with confirmed or suspected STI 1
Step 4: Treatment Decision
- If STI is confirmed or highly suspected with pyuria present, treat the STI and await urine culture results before adding UTI antibiotics 1, 6
- Reliance on pyuria or positive nitrite for empirical UTI treatment in cases where STI is confirmed or highly suspected results in substantial overtreatment 1
Key Takeaway for Clinical Practice
The presence of leukocytes on urinalysis cannot distinguish between STI-related urethritis/cervicitis and bacterial UTI. The critical error is assuming pyuria equals UTI without considering STI as the cause of inflammation. Always test for STIs in at-risk patients presenting with genitourinary symptoms and pyuria, and avoid empirical UTI treatment until bacterial infection is confirmed by culture 1, 6, 2.