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Cervical cytology: Evaluation of atypical squamous cells (ASC-US and ASC-H)

Annekathryn Goodman, MD
Warner K Huh, MD
Section Editor
Barbara Goff, MD
Deputy Editor
Sandy J Falk, MD, FACOG


Cervical cytology became the standard screening test for cancer of the uterine cervix and premalignant cervical lesions with the introduction of the Papanicolaou (Pap) smear in 1941 [1]. The addition of human papillomavirus testing to cervical cancer screening strategies has improved detection of cervical neoplasia and allowed further risk stratification.

Current terminology for reporting cervical cytology results includes the category atypical squamous cells (ASC), which differ from normal cells but do not meet criteria for a premalignant disease (squamous intraepithelial neoplasia [SIL]). ASC can be categorized as ASC-US, "of undetermined significance," or ASC-H, in which a high-grade squamous intraepithelial lesion (HSIL) cannot be excluded [2]. A finding of ASC-H is associated with a markedly higher risk of premalignant disease or cervical cancer than ASC-US. (See 'Risk of premalignant or malignant disease' below.)

Evaluation of women with cervical cytology with atypical squamous cells is reviewed here. Cervical cancer screening strategies and techniques, interpretation of cervical cytology results, follow-up of other abnormal cytology results, and management of cervical neoplasia are discussed separately. (See "Screening for cervical cancer" and "Cervical cancer screening tests: Techniques for cervical cytology and human papillomavirus testing" and "Cervical and vaginal cytology: Interpretation of results (Pap test report)" and "Cervical cytology: Evaluation of low-grade squamous intraepithelial lesions (LSIL)" and "Cervical cytology: Evaluation of high-grade squamous intraepithelial lesions (HSIL)" and "Cervical cytology: Evaluation of atypical and malignant glandular cells" and "Cervical intraepithelial neoplasia: Management of low-grade and high-grade lesions".)


Terminology used to describe cervical cancer screening tests or cervical cytology results discussed here includes:

Atypical squamous cells of undetermined significance (ASC-US) – Cells that display abnormalities more marked than simple reactive changes but do not display a squamous intraepithelial lesion (SIL).

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Literature review current through: Nov 2017. | This topic last updated: Nov 28, 2017.
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