What Are the Causes of Atypical Pap Smear?

The National Cancer Institute estimates that approximately 55 million Pap smears are performed in the United States every year. Of those, about 6 percent return results that are considered atypical or abnormal and require follow-up or re-testing.

• Annual Pap smears help screen women for cervical disease.

Dysplasia

• Abnormal or atypical cells may take the form of dysplasia. These non-cancerous or pre-cancerous cells, which look abnormal under a microscope, are classified in four degrees, depending on their severity or appearance: mild, moderate, severe or carcinoma in situ.

Squamous Intraepithelial Lesions

• Squamous intraepithelial lesions, or SILs, are flat, thin cells that appear on the outer surface of the cervix. SILs can be classified as low grade or high grade depending on the number and spread of the cells.

ASCUS

• Atypical squamous cells of undetermined significance (ASCUS) are one of the most common reasons for an atypical Pap smear. These non-cancerous or pre-cancerous cells can be caused by HPV (human papillomavirus), a common and often silent sexually transmitted infection.

Cervical Intraepithelial Neoplasia

• Cervical intraepithelial neoplasia (CIN) describes an atypical growth of cell groups along the cervix. CIN is assigned a number, 1 through 3, that describes how much of the cervical lining contains these kinds of cells.

Other Atypical Cells

• The lab may alert your doctor to the presence of atypical glandular or squamous cells. These are cells that appear slightly atypical or abnormal, but their significance requires further testing.