Since the Pap smear was introduced in 1943, a number of methods have been developed to classify the results. The two methods commonly used today are the Bethesda System and the CIN Grading System.
The Bethesda System was developed by the Centers for Disease Control and Prevention (CDC) and National Institutes of Health (NIH) in order to have a comprehensive and standardized method of classifying Pap smear results. It uses the term squamous intraepithelial lesion (SIL) to describe abnormal changes in the cells on the surface of the cervix. Squamous refers to thin, flat cells that lie on the outer surface of the cervix. An intraepithelial lesion occurs when normal cells on the cervical surface are replaced by a layer of abnormal cells, and these changes are classified as high grade or low grade.
Bethesda System
- Atypical squamous cells of undetermined significance (ASCUS)—Borderline, some abnormal cells
- Low-grade intraepithelial lesions (LGSIL)—Mild dysplasia and cellular changes associated with HPV
- High-grade squamous intraepithelial lesions (HGSIL)—Moderate to severe dysplasia, precancerous lesions, and carcinoma in-situ (preinvasive cancer that involves only the surface cells)
Squamous Cell Carcinoma
Cervical intraepithelial neoplasia (CIN) refers to new abnormal cell growth. Intraepithelial refers to the surface layers of the cells. The CIN System grades the degree of cell abnormality numerically, CIN I is the lowest and CIN III is the highest.
CIN Grading System
- Atypia—correlates with ASCUS
- CIN I—mild dysplasia and correlates with LGSIL
- CIN II—moderate dysplasia and correlates with HGSIL
- CIN III—severe dysplasia and correlates with HGSIL
- Carcinoma in-situ
- Cervical cancer
Physician-developed and -monitored.
Original Date of Publication: 01 Oct 2001
Reviewed by: Stanley J. Swierzewski, III, M.D.
Last Reviewed: 11 Aug 2008
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