Final answer:
To diagnose a yeast infection, the KOH preparation is the preferred test. It allows the clear identification of fungal cells indicative of candidiasis by dissolving other cellular material. Upon confirmation, antifungal medication is typically prescribed.
Step-by-step explanation:
To obtain a diagnosis of a yeast infection, the test of choice is KOH preparation. This method involves treating the vaginal discharge with potassium hydroxide (KOH) to better visualize the yeast cells under a microscope. Although other methods like Gram stain, wet mount, and culture can provide additional information or help rule out other infections, a KOH preparation is particularly useful for identifying the fungal cells characteristic of candidiasis, the condition caused by an overgrowth of yeast. The KOH dissolves the bacterial and cellular material, allowing the fungal cells and pseudohyphae typical of Candida spp. to be seen more clearly. Following the confirmation of a yeast infection diagnosis, the physician may prescribe an antifungal drug to treat the candidiasis.