A clue cell is an epithelial cell found in the vagina, examined under a vaginal fluid wet mount with a microscope. Epithelial cells are distinctive in appearance, as they are covered in bacteria. The name ‘clue cell’ was invented by Gardner and Dukes, who were the first researchers looking into bacterial vaginosis and Gardnerella vaginalis.
Epithelial cells are a type of skin cell, which you can think of as the outer layer of skin cells. These cells slough off and are lost. In the vagina, this loss is via normal vaginal secretions, which exit the body eventually via gravity.
When these cells are coated in bacteria – which is not normally the case – it indicates a vaginal problem, namely bacterial vaginosis (BV). Looking for clue cells is part of a group of tests usually performed, called Amsel’s criteria. Amsel’s criteria is a pH test (normal vaginal pH is between 3.8 and 4.5, while BV causes a much more alkaline vaginal pH, above 4.5), the whiff test, and a look under the microscope for clue cells. All of these things can be done in your doctor’s office.