STD Testing During Menstruation: Accuracy Concerns and Best Timing

Why Menses Can Interfere

• Blood contaminates swabs/urine → false negatives (dilution, PCR inhibition).
• Cervical cytology changes → harder to collect adequate endocervical cells.
• Altered vaginal pH/flora → affects culture/NAAT for some organisms.
• Patient discomfort → suboptimal sampling.

Tests Affected

• NAAT (chlamydia, gonorrhea, trichomonas) – urine or swab.
• Culture (GC, trichomonas).
• Wet mount (BV, yeast, trich).
• Pap/HPV co-testing.

Best Practice

1. Schedule testing after menses ends.
2. If urgent (symptoms, exposure): clinician may proceed with awareness of limitations.
3. Urine NAAT less affected than swabs; first-catch urine preferred.
4. Blood tests (HIV, syphilis, HSV serology) unaffected.

Bottom Line

Wait until period finishes for optimal accuracy. If tested during, repeat after menses if negative but risk persists.