What is the diagnostic approach for vulvovaginal yeast infection?

Diagnostic Approach for Vulvovaginal Yeast Infection

Vulvovaginal candidiasis should be diagnosed using a combination of clinical presentation and microscopic examination showing yeast or pseudohyphae, with culture reserved for recurrent or complicated cases to identify non-albicans species and guide therapy. 1

Clinical Presentation

The hallmark symptom of vulvovaginal candidiasis (VVC) is vulvar pruritus, accompanied by thick white discharge, vulvar burning, dyspareunia, and external dysuria. 2 Critically, the vaginal pH remains normal (≤4.5), which distinguishes VVC from bacterial vaginosis (pH >4.5) and trichomoniasis (pH >4.5). 2, 1

Physical examination should focus on identifying vulvar erythema, edema, and the characteristic thick, white, "cottage cheese-like" discharge adherent to the vaginal walls. 1

Diagnostic Testing Algorithm

First-Line: Microscopy

• Obtain a vaginal swab and prepare two slides: one with 0.9% normal saline and one with 10% potassium hydroxide (KOH). 1
• The KOH preparation is superior for identifying yeast cells and pseudohyphae, as it dissolves epithelial cells and enhances visualization. 1
• Microscopy has sensitivity of 40-70% compared to culture, meaning negative microscopy does not rule out VVC. 1

When Microscopy is Negative but Clinical Suspicion Remains High

• Order fungal culture on Sabouraud medium, which takes 48-72 hours and serves as the gold standard for diagnosis. 1, 3
• Culture is particularly valuable because it identifies the specific Candida species and allows susceptibility testing if needed. 1

Molecular Testing (PCR)

• PCR for Candida group (C. albicans, C. dubliniensis, C. parapsilosis, C. tropicalis) demonstrates high accuracy: sensitivity 90.9%, specificity 94.1%. 1
• PCR is superior to clinical microscopy (sensitivity 90.7% vs 57.5%) and provides same-day results, avoiding the 48-72 hour culture delay. 1
• For C. glabrata, PCR sensitivity is lower (75.9%) but specificity remains excellent (99.7%). 1
• Multiplex NAAT panels can simultaneously detect VVC, bacterial vaginosis, and trichomoniasis in a single test. 1

Critical Diagnostic Pitfalls

Avoid Overdiagnosis

• 10-20% of asymptomatic women harbor Candida species in the vagina as normal colonizers. 2
• Never treat based on culture alone without corresponding symptoms—this leads to unnecessary treatment of colonization. 2
• Less than half of patients clinically diagnosed and treated for VVC actually have the infection when objective testing is performed. 1

Evaluate for Mixed Infections

• VVC frequently coexists with sexually transmitted infections. 2
• Always assess vaginal pH to distinguish VVC (pH ≤4.5) from bacterial vaginosis or trichomoniasis (pH >4.5). 2, 1
• Consider testing for Trichomonas vaginalis using NAAT, as wet mount sensitivity is only 40-80%. 4

Recurrent or Complicated Cases Require Culture

• For women with recurrent VVC (≥4 episodes per year) or treatment failure, culture is mandatory to identify non-albicans species. 1, 3
• 10-15% of recurrent cases involve resistant Candida species (C. glabrata, C. krusei) that require alternative antifungal therapy. 1
• In complicated cases, consider repetitive cultures taken by the patient herself during symptomatic episodes to capture intermittent shedding. 3

Don't Ignore the Vaginal Reservoir

• Even when only vulvitis is evident, thorough examination of vaginal fluid is obligatory because the vagina is invariably the reservoir for recurrent vulvar infections. 3
• Bedside phase-contrast microscopy of fresh vaginal fluid by experienced clinicians improves diagnostic accuracy in complicated cases. 3

Specimen Collection and Transport

• Vaginal swab of discharge is the optimal specimen. 1
• For microscopy: submit in 0.5 mL saline or transport swab, room temperature, within 2 hours. 1
• For culture: submit in transport swab, room temperature, within 12 hours. 1
• For molecular testing: follow manufacturer's recommendations, typically room temperature for 7 days. 1

When Laboratory Testing Fails

Laboratory testing fails to identify a cause in 25-40% of women with vaginitis symptoms. 1, 4 In these cases, consider non-infectious causes including atrophic vaginitis, irritant or allergic vaginitis, or inflammatory vaginitis, which account for 5-10% of cases. 5