Diagnostic Testing for Vaginal Discharge
Order a wet prep with pH testing as your immediate point-of-care test, combined with NAAT testing for Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis to ensure comprehensive diagnosis. 1, 2
Initial Point-of-Care Testing
Wet prep microscopy is your first-line diagnostic tool because it provides immediate visualization of the three most common causes of vaginitis (bacterial vaginosis, trichomoniasis, and vulvovaginal candidiasis), which account for approximately 90% of cases. 1
Wet Prep Components:
Saline wet mount: Examine pooled vaginal secretions immediately to identify clue cells (bacterial vaginosis), motile flagellated trichomonads (trichomoniasis), and white blood cells. 3, 1
10% KOH preparation: Enhances visualization of pseudohyphae and budding yeast for candidiasis diagnosis, and produces the characteristic "fishy" odor indicating bacterial vaginosis. 3, 1
Vaginal pH testing: Normal pH <4.5 suggests candidiasis, while pH >4.5 indicates bacterial vaginosis or trichomoniasis. 1, 4
Critical Timing Requirement:
The wet prep must be examined within 30 minutes to 2 hours of collection, as motile trichomonads lose viability and become undetectable after this window. 1, 2
Concurrent NAAT Testing
Always order NAAT testing simultaneously with wet prep, as microscopy alone has significant limitations. 1, 2
NAAT Panel Should Include:
Chlamydia trachomatis and Neisseria gonorrhoeae: NAAT is the gold standard for these sexually transmitted infections. 2
Trichomonas vaginalis: NAAT is essential because wet prep sensitivity is only 40-80%, meaning a negative wet prep does not rule out infection. 1, 2
The same specimen collection device can often be used for all three organisms, and specimens remain stable at room temperature for 2-7 days depending on the specific assay. 2
Additional Testing Based on Clinical Findings
For Bacterial Vaginosis Confirmation:
Quantitative Gram stain (Nugent criteria) is the most specific procedure for bacterial vaginosis diagnosis, though wet prep with Amsel criteria is sufficient for routine clinical diagnosis. 2
The specimen is stable at room temperature for 12 hours when placed directly into a transport swab tube. 2
For Recurrent or Persistent Yeast Infections:
Culture is mandatory to identify non-albicans Candida species that may require different treatment. 2, 4
Multiplex NAAT panels can detect C. albicans and resistant species in a single test. 2
For Genital Ulcers or Lesions:
- Viral culture for HSV and serologic tests for syphilis should be performed for suspicious ulcers, as these are the most common causes of genital ulcers in the United States. 3
Specimen Collection Technique
Collect vaginal swabs from pooled vaginal discharge or lateral vaginal walls, avoiding contamination with cervical mucus as this affects test accuracy. 2 For NAAT testing, vaginal swabs, endocervical swabs, or urine can be used. 2
Common Pitfalls to Avoid
Never rely solely on wet mount for Trichomonas diagnosis given its poor sensitivity of 40-80%. 1, 2
Don't delay wet mount examination beyond 2 hours, as organisms lose motility and become undetectable. 1, 2
Don't forget concurrent STI testing, as many infections coexist with vaginitis. 1, 4
Don't culture Gardnerella vaginalis for bacterial vaginosis diagnosis, as it lacks specificity. 1
Don't assume normal pH excludes all infections: yeast typically has pH <4.5, while bacterial vaginosis and Trichomonas have pH >4.5. 2
When Physical Examination Matters
During speculum examination, note cervical friability and hyperemia (indicating possible STI), white plaques on the cervix (possible condyloma acuminata), or red punctate lesions suggesting trichomoniasis. 3 However, symptoms and physical signs alone are insufficient to distinguish specific etiologic agents, making diagnostic testing critical. 5, 6