Cause

Most abnormal Pap tests are caused by human papillomavirus (HPV) infections. Other types of infection—such as those caused by bacteria, fungi (yeast), or protozoa (Trichomonas)—sometimes lead to minor changes on a Pap test called atypical squamous cells of undetermined significance (ASC-US). The most common cause is HPV infection. Natural cervical cell changes (atrophic vaginitis) related to menopause can also cause an abnormal Pap test.

• The cervix contains two kinds of cells: rectangular-shaped columnar cells on the surface of the cervix and in the cervical canal; and flat, scalelike squamous cells on the surface of the cervix.
• Columnar cells are constantly changing into squamous cells in an area of the cervix called the transformation zone.
• Because cells in this area of the cervix are always dividing, they are at risk for abnormal changes. Most abnormal cell changes found during a Pap test are from the transformation zone.