What are the best tests to run for vaginal discharge in Australian labs, including standard sexually transmitted infections (STIs), bacterial vaginosis, and pH levels?

Optimal Laboratory Testing for Vaginal Discharge in Australian Labs

For vaginal discharge evaluation in Australian laboratories, order nucleic acid amplification testing (NAAT) for Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis as your primary STI screen, combined with either a multiplex NAAT vaginal panel (if available) or traditional microscopy with pH testing and Gram stain for bacterial vaginosis and yeast diagnosis. 1

Primary STI Testing

Standard STI Screen:

• NAAT for Chlamydia trachomatis and Neisseria gonorrhoeae is the gold standard, with the same specimen collection device often used for both organisms 1
• NAAT for Trichomonas vaginalis should be included simultaneously, as Trichomonas prevalence equals or exceeds CT/GC in certain populations and NAAT offers superior sensitivity (far better than the 40-80% sensitivity of wet mount) 1, 2
• Specimens remain stable at room temperature for 7 days, allowing flexibility in transport to Australian reference laboratories 1, 2

Bacterial Vaginosis Testing

For BV diagnosis, you have two evidence-based approaches:

Gold Standard Approach:

• Quantitative Gram stain (Nugent criteria) is the most specific procedure for bacterial vaginosis diagnosis 1, 3
• Place swab directly into transport swab tube, stable at room temperature for 12 hours 1
• This provides objective scoring of bacterial morphotypes and eliminates the subjectivity of clinical criteria 3

Alternative Molecular Approach:

• DNA hybridization probe or multiplex NAAT for microbiome-based BV detection (such as BD Max Vaginal panel) detects Gardnerella vaginalis and other BV-associated organisms 1, 3
• Specimens stable up to 7 days at room temperature 1
• These newer molecular tests provide objective results and can detect fastidious bacteria 3

Point-of-Care Testing (if microscopy available):

• Vaginal pH testing - BV typically shows pH >4.5 1, 3
• Wet mount with 10% KOH for clue cells and whiff test 1, 3
• Submit swab in 0.5 mL saline or transport swab, must reach lab within 2 hours 1

Critical caveat: Culture is NOT recommended for BV diagnosis 1

Yeast Vaginitis Testing

Diagnostic algorithm for Candida:

First-Line Approach:

• Microscopic examination with 10% KOH preparation to visualize yeast or pseudohyphae 1, 4
• Vaginal pH measurement - yeast typically shows pH <4.5 (if >4.5, consider BV or Trichomonas instead) 1, 4
• Sensitivity of KOH microscopy is only 40-80%, meaning it misses 20-60% of true infections 4

When to Order Culture:

• Culture is mandatory for recurrent infections to identify non-albicans Candida species (C. glabrata, C. krusei) that may require different treatment 4
• Order culture when microscopy is negative but clinical suspicion remains high (pH <4.5, classic symptoms) 4
• Submit swab in transport medium, stable at room temperature for 12 hours 1

Molecular Alternative:

• Multiplex NAAT panels (such as BD Max Vaginal panel) can detect C. albicans and resistant species (C. glabrata/krusei) in a single test 1, 4
• FDA-cleared for symptomatic females 1, 4

Practical Specimen Collection

Optimal specimen collection:

• Use a vaginal swab from pooled vaginal discharge or lateral vaginal walls 3
• Avoid contaminating with cervical mucus as this affects test results 3
• For NAAT testing, vaginal swabs, endocervical swabs, or urine can be used 1, 2

Critical Pitfalls to Avoid

Common mistakes that compromise diagnosis:

1. Never rely solely on wet mount for Trichomonas - its sensitivity is only 40-80% and requires living organisms examined within 30 minutes to 2 hours 1, 2

2. Don't use wet mount/KOH alone for BV diagnosis - wide variation in sensitivity (40-70%) exists, and consistent microscopic interpretation is difficult 1, 3

3. Don't skip culture in recurrent yeast infections - approximately 15% of C. albicans organisms are resistant to common azoles, and non-albicans species are increasingly prevalent 5

4. Don't assume normal pH excludes all infections - yeast typically has pH <4.5, while BV and Trichomonas have pH >4.5 1, 4

5. Don't delay wet mount examination beyond 2 hours if using this method, as organisms lose motility and become undetectable 1, 2

Recommended Testing Panel for Australian Labs

Comprehensive vaginal discharge workup:

• NAAT for CT/GC/Trichomonas (single multiplex test if available) 1
• Gram stain for BV (Nugent criteria) OR molecular BV testing 1, 3
• Vaginal pH measurement 1, 3, 4
• KOH microscopy for yeast 1, 4
• Culture for Candida if recurrent infection or microscopy negative with high suspicion 4

For pregnant patients: Testing and treatment for BV is particularly important to reduce postpartum endometritis 1