What is the best specimen to collect from a patient suspected of having a Sexually Transmitted Disease (STD)?

Best Specimen for STD Testing

For a patient with suspected STD, first-void urine (midstream urine) is the optimal specimen choice for detecting the most common sexually transmitted infections (Chlamydia trachomatis and Neisseria gonorrhoeae) using nucleic acid amplification tests (NAATs), particularly in males, while urethral swabs remain an acceptable alternative.

Specimen Selection by Patient Sex

For Male Patients

• First-void urine is the preferred specimen for detecting both C. trachomatis and N. gonorrhoeae using NAATs 1, 2.
• First-void urine (the first 20-30 mL of any micturition) demonstrates sensitivity of 94-96% for chlamydia detection, comparable to urethral swabs 3, 4.
• Urine collection is non-invasive, non-traumatic, and highly acceptable to patients compared to urethral swabbing 3.
• Urethral swabs are an acceptable alternative when urethral discharge is present or when culture (rather than NAAT) is required 1.
• The urethra should be sampled by inserting the swab 2-4 cm and rotating for at least 5 seconds 1.

For Female Patients

• Vaginal swabs (self-collected or clinician-collected) are the optimal specimen for NAAT testing 1.
• First-void urine is acceptable but may have slightly reduced performance compared to vaginal or cervical specimens 1.
• For comprehensive detection, combining urine with a cervical specimen increases sensitivity 2.
• The endocervix is preferred when culture methods are used, requiring insertion 1-2 cm past the squamocolumnar junction with rotation for 10-30 seconds 1.

Why Other Options Are Suboptimal

Semen (Option C)

• Semen is not a standard specimen for STD diagnosis and is not mentioned in any major guidelines for routine STD screening 1.
• No validated testing protocols exist for common STDs using semen.

Blood (Option D)

• Blood is only appropriate for serologic testing (syphilis, HIV, hepatitis) but not for detecting urogenital infections like gonorrhea or chlamydia 1.
• Blood cannot detect the most common treatable STDs (C. trachomatis, N. gonorrhoeae, T. vaginalis) 1.

Critical Technical Considerations

Timing and Collection

• For urethral specimens, delay collection until at least 2 hours after the patient has voided 1.
• For first-void urine, timing of last void (up to 8 hours) has minimal effect on NAAT positivity 4.
• Use manufacturer-specified swabs for NAAT testing, as different platforms have specific requirements 1, 5.

Specimen Quality

• The objective is to obtain columnar epithelial cells, not just secretions or discharge 1, 5.
• Improperly collected specimens will yield inaccurate results regardless of test quality 1, 5.
• Greater than 10% of specimens may be unsatisfactory without quality assurance protocols 1.

High-Risk Populations Requiring Additional Sites

Men Who Have Sex with Men (MSM)

• Require extragenital site testing (rectal and oropharyngeal swabs) in addition to urethral/urine specimens 1.
• Rectal swabs should be inserted 1-2 cm into the anal canal and rotated for 10-30 seconds 5.
• Annual screening at all exposure sites is recommended 1.

Common Pitfalls to Avoid

• Do not collect only the second or third void - amplified test positivity declines precipitously in subsequent voids 4.
• Do not freeze female urine specimens before processing for M. genitalium testing, as this causes 27% false-negative results 2.
• Do not use nonculture tests in forensic/abuse cases - only standard culture with high specificity should be used due to legal implications 1.
• Do not assume urine alone is sufficient in women - supplement with cervical or vaginal specimens for optimal sensitivity 2.