What tests should be run to diagnose persistent vaginal itching?

Diagnostic Tests for Persistent Vaginal Itching

For persistent vaginal itching, the most appropriate diagnostic approach is to perform pH testing of vaginal secretions followed by microscopic examination with saline wet mount and 10% potassium hydroxide (KOH) preparations to identify the specific cause. 1

Initial Assessment

pH Testing

• Collect vaginal discharge and test pH using narrow-range pH paper
• Interpretation:
  • pH <4.5: Suggests yeast infection (vulvovaginal candidiasis)
  • pH >4.5: Suggests bacterial vaginosis or trichomoniasis 1

Microscopic Examination

1. Saline Wet Mount:

   • Place vaginal discharge in 0.5 mL saline or directly on slide with a drop of saline
   • Look for:
     • Motile trichomonads (trichomoniasis)
     • Clue cells (bacterial vaginosis) - epithelial cells covered with bacteria
     • White blood cells (inflammatory response)
     • Yeast cells or hyphae (though better seen with KOH) 1

2. 10% KOH Preparation:

   • Place vaginal discharge on slide with a drop of KOH
   • Look for:
     • Yeast pseudohyphae or budding yeast cells (candidiasis)
     • Perform "whiff test" - fishy odor after adding KOH suggests bacterial vaginosis 1

Advanced Testing Options

For Yeast Infections

• Culture: Consider when microscopy is negative but symptoms suggest yeast infection
  • Particularly useful for recurrent cases to identify non-albicans Candida species 1, 2
• DNA Hybridization Probe: Detects Candida albicans with higher sensitivity than microscopy
  • Specimen stable at room temperature for up to 7 days 1

For Bacterial Vaginosis

• Quantitative Gram Stain: Most specific procedure for diagnosing BV
  • Place vaginal discharge directly into transport swab tube 1
• DNA Hybridization Probe: Detects Gardnerella vaginalis
  • Does not rely on viable organisms for test performance 1
• Amsel Criteria: Diagnosis requires 3 of 4 criteria:
  1. Homogeneous white discharge
  2. Clue cells on microscopy
  3. pH >4.5
  4. Positive whiff test (fishy odor with KOH) 1

For Trichomoniasis

• Nucleic Acid Amplification Test (NAAT): Most sensitive method
  • Can be performed on vaginal, endocervical swabs, or urine samples 1
• Rapid Antigen Test: More sensitive than wet mount (62-95%)
  • Does not require live organisms 1
• Culture: Consider when microscopy is negative but trichomoniasis is suspected
  • InPouch TV culture system allows both immediate review and subsequent culture 1

Special Considerations

• If all infectious testing is negative, consider:

  • Atrophic vaginitis (especially in postmenopausal women)
  • Contact or allergic dermatitis
  • Irritant vaginitis from soaps, douches, or other products
  • Inflammatory vaginitis 2, 3

• For persistent or recurrent symptoms despite negative initial testing:

  • Repeat testing during symptomatic episodes
  • Consider expanded testing for less common causes
  • Evaluate for potential underlying conditions (diabetes, immunosuppression) 3

Common Pitfalls to Avoid

1. Relying solely on symptoms: Different causes of vaginal itching can present similarly; laboratory confirmation is essential 2

2. Inadequate specimen collection: Collect discharge from the vaginal walls rather than just the introitus for more accurate results

3. Delayed specimen processing: Wet mount sensitivity for trichomonads decreases significantly after 30 minutes; optimal processing time is within 2 hours 1

4. Missing mixed infections: Multiple pathogens can coexist; thorough microscopic examination is important 1

5. Failure to consider non-infectious causes: When infectious testing is repeatedly negative, consider other etiologies like irritants, allergens, or inflammatory conditions 3