STI Testing in Males: Urine vs. Urethral Swab
For diagnosing sexually transmitted infections (STIs) in males, urine testing is the preferred method over urethral swabs due to its non-invasive nature, comparable sensitivity and specificity, and greater patient acceptability.
Diagnostic Test Performance
- Urine tests using enzyme immunoassay (EIA) for detecting Chlamydia trachomatis show excellent sensitivity (94%) and specificity (99%) compared to urethral swabs (97% sensitivity, 99% specificity) in symptomatic men 1.
- First-catch urine specimens are non-invasive and non-traumatic compared to urethral swabs, making them more acceptable to patients while maintaining diagnostic accuracy 1, 2.
- Modern nucleic acid amplification tests (NAATs) have further improved the sensitivity of urine-based testing, making it the current standard of care 3.
Testing Recommendations Based on Symptoms
Symptomatic Males
- For men with symptomatic urethritis, both urethral swabs and urine tests are highly effective for detecting chlamydial infections 4.
- Urethral specimens from symptomatic men using EIA tests show sensitivities that usually exceed 70%, with specificities of 97-99% 4.
- The leucocyte esterase test (LET) on urine can be used as an initial screening tool for urethritis in symptomatic patients, with a sensitivity of 94% for detecting urethral infection 5.
Asymptomatic Males
- For asymptomatic men, urine-based NAATs are preferred due to higher acceptability and adequate sensitivity 3, 2.
- Traditional non-culture tests on urethral specimens have limited sensitivity in asymptomatic men and are not recommended for this population 4.
- Screening tests using urine rather than intraurethral swabs are more acceptable to patients, increasing screening compliance 4.
Special Considerations
- The Centers for Disease Control and Prevention (CDC) recommends assessing sexual practices to determine appropriate anatomical sites for testing 6.
- For men who have sex with men (MSM), additional pharyngeal and rectal testing may be necessary based on sexual practices 6.
- Self-collected rectal swabs have shown comparable sensitivity to clinician-collected specimens, while self-collected glans swabs have shown disappointing sensitivity for C. trachomatis detection 7.
Testing Algorithm
- First-line testing: First-catch urine specimen using NAAT for all males (symptomatic and asymptomatic) 1, 3, 2.
- Symptomatic patients: If urine testing is not available, urethral swab specimens can be used with comparable accuracy 4.
- Additional sites: Based on sexual history, consider pharyngeal and/or rectal swabs for MSM who engage in receptive oral or anal intercourse 6.
Pitfalls and Caveats
- False-positive results may occur with urine tests in older men with non-chlamydial urinary tract infections 4.
- Urine specimens should be first-catch urine or collected at least 2 hours after previous urination for optimal sensitivity 2.
- Post-treatment testing using non-culture methods should be scheduled at least 3 weeks after completion of antimicrobial therapy to avoid false results 4.