You know the routine: undress, change into a medical gown, wait for your OB-GYN, then rest your feet in the stirrups. But despite their familiarity, the purpose of a Pap smear remains unclear. You know it has something to do with cervical cancer, and that something is collected and sent away for examination. But what are they looking for? 

Jennifer Hill, a certified nurse practitioner, explains that Pap smears screen for precancerous cells in the cervix, known as cervical dysplasia. In other words, the exam doesn’t look for cancer, but any cells with the potential to become cancer. 

“People hear the word ‘cancer’ in precancerous and get concerned. But there are several levels of abnormality before we get to cancer,” she says. “If they follow up as recommended, we’re going to prevent it from ever turning to cancer.”

Most Pap smears come back normal. But if you receive an abnormal result, don’t panic.

All an abnormal result means is there are changes in your cervical cells, either low or high grade. 

Low-grade changes  

A low-grade result suggests minor changes in your cervical cells. Of the different kinds of low-grade results, not all are considered precancerous. 

Atypical squamous cells of undetermined significance

Jennifer says the result she sees most often is atypical squamous cells of undetermined significance (ASC-US). This means the cells are slightly abnormal.

“The cells are not precancerous, but they are not typical,” she says. “So they are somewhere in between.” 

This may be from human papillomavirus (HPV). But it can also be from inflammation caused by a bacteria or yeast infection.  

Low-grade squamous intraepithelial lesions

Low-grade squamous intraepithelial lesions (LSIL) means there is a mild yet clear abnormality in the cells. Like ASC-US, this is most likely from an HPV infection. But unlike AS-CUS, an LSIL result is considered precancerous. 

Most HPV cases and low-grade abnormalities resolve on their own. 

“Which is why sometimes,” Jennifer says, “especially for a younger person, the recommendation is just to repeat the Pap smear after a year.”

High-grade changes 

Some Pap smear results show a high-grade, or major, change in the cervical cells. Although these have a higher risk of becoming cancerous, routine screenings help your OB-GYN catch and treat them before that happens. 

High-grade squamous intraepithelial lesions 

High-grade squamous intraepithelial lesions indicate a significant abnormality of the cervical cells, also usually caused by HPV. 

Jennifer explains that along with routine Pap smears, the best way to prevent cervical cancer is by getting the HPV vaccine. 

“The vaccine protects against the two ‘super villain’ HPV strains, which are responsible for the vast majority of cervical cancers.” 

Atypical glandular cells 

The cervix has two types of cells: squamous cells, which form the outermost layers, and glandular cells, which form the innermost layers. Most abnormal Pap smear results indicate a change in the squamous cells, but atypical glandular cells reveal a change in those innermost cells. 

According to Jennifer, this could indicate advanced dysplasia or a more serious problem in the cervix or uterus. 

Knowledge is health

Thinking about getting an abnormal result can be scary. But, Jennifer says, “It’s important to get regular screenings so we can identify a problem before it turns to cervical cancer.”