ASC-US of the cervix

What does ASC-US mean?

ASC-US stands for atypical squamous cells of undetermined significance. ASC-US means that abnormal-looking cells were seen on your Pap test. ASC-US is a preliminary result and not a final diagnosis. Conditions associated with ASC-US include non-cancerous changes such as inflammation in the cervix and the pre-cancerous disease low grade squamous intraepithelial lesion (LSIL). The cells in ASC-US are not cancer cells.


The cervix

The cervix is part of the female genital tract. It is found at the bottom of the uterus where it forms an opening into the endometrial cavity. The narrow passage that runs through the cervix from the endometrium to the vagina is called the endocervical canal.

The part of the cervix inside the vagina is called the exocervix. It is covered by special cells called squamous cells. These cells form a barrier called the epithelium that protects the cervix. The endocervical canal is covered by different kinds of cells that connect to form endocervical glands. The area of the cervix where the exocervix meets the endocervical canal is called the transformation zone. Most cancers of the cervix start in the transformation zone.

Why is the Pap test performed?

The Pap test is a screening test designed to look for pre-cancerous and cancerous cells in the cervix. Read our introduction article to learn more about the Pap test.

What causes ASC-US?

ASC-US is a relatively common Pap test result in women of all ages. Causes of ASC-US include human papillomavirus (HPV) infection, inflammation of the cervix, postmenopausal status, and prior radiation therapy.

For most patients, the condition that caused the changes seen in ASC-US will resolve on its own over time. However, because ASC-US can be associated with LSIL or other more serious conditions such as high-grade squamous intraepithelial lesion (HSIL) or squamous cell carcinoma, your doctor should arrange for you to have another Pap test in 6 months.

A repeat Pap test in 6 months is recommended for women with ASC-US to see if the condition has resolved.

What does ASC-US look like under the microscope?

When examined under the microscope, the abnormal squamous cells in ASC-US have larger nuclei and a slightly increased ratio of nuclear to cytoplasmic area compared to nearby normal squamous cells. The nuclei can also be slightly darker and have irregular nuclear membranes. Pathologists call cells that look darker than other cells hyperchromatic.

ASC-US in women under 30 years of age

According to the current guidelines, women who are < 30 years of age with ASC-US should have a repeat Pap test in 6 months. If ASC-US is seen again, another Pap test is performed in 6 months. If ASC-US still persists, your doctor should refer you to a specialist who will perform a colposcopy.

ASC-US in women 30 years of age or older

For women 30 years of age or older with ASC-US, the tissue collected during the Pap test should be sent for human papillomavirus (HPV) testing. This test looks for specific high-risk types of HPV that are known to cause cervical cancer.

If a high-risk type of HPV is found in your sample, your doctor should refer you to a specialist who will perform a colposcopy. Finding high-risk HPV does not mean that you have cervical cancer. It does mean, however, that you are at higher risk of developing a pre-cancerous or cancerous growth, and that a closer follow-up with your gynecologist and family physician is required.


A colposcopy allows your doctor to see the entire outer surface of the cervix. During the colposcopy, the doctor will be looking for any areas that look abnormal on the surface of the cervix. If an abnormality is found, the doctor may decide to take a small sample of tissue called a biopsy to look for pre-cancerous and cancerous changes. Your doctor may also take a biopsy from the endocervical canal and endometrium.

Other helpful resources:

Choosing Wisely Canada

Cancer Care Ontario

by Adnan Karavelic, MD FRCPC (updated June 25, 2021)
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