A 32-year-old woman comes to the clinic for evaluation of multiple episodes of vulvar itching and thick, white vaginal discharge over the past 10 months. Each episode improved with OTC intravaginal azole therapy but recurred within 4–6 weeks. She is in a monogamous relationship and does not douche. She reports increased thirst and urination over the last several months. BMI is 33 kg/m2. Pelvic exam shows vulvar erythema and adherent white discharge. Vaginal pH is 4.2. Wet mount shows oval budding yeast forms with pseudohyphae. Which of the following is the most appropriate next step in management to evaluate an underlying condition contributing to her recurrent infections?