 [ Symptoms ] how is thrush diagnosed [ Disease ] your dentist can diagnose thrush by examining your mouth he or she looks for the distinctive white lesions on your mouth tongue or cheeks lightly brushing the lesions away reveals a reddened tender area that may bleed slightly a microscopic examination of tissue from a lesion can confirm the diagnosis thrush that extends into your esophagus may require other tests to make the diagnosis such tests might include taking a throat culture swabbing the back of your throat with sterile cotton and studying the microorganisms under a microscope performing an endoscopy of your esophagus stomach and small intestine examining the lining of these body areas with a lighted camera mounted on the tip of a tube passed through these areas or taking x rays of your esophagus