Bethesda System for Reporting Cervical Cytology
Classification of Pap test results, based on the Bethesda System for reporting cervical cytology, was first introduced in 1988 and revised in 2001 to define satisfactory samples and to standardize reporting.
Inadequate samples for evaluation include those tests that lack patient identifying information, broken slides, inadequate squamous component (defined as < 5000 squamous cells on liquid-based medium or < 8000 to 12,000 cells on conventional medium), or obscuring elements on over 75% of squamous cells (typically due to lubricant, inflammation, or blood).
The Bethesda System terminology for cytologic reporting classifies epithelial abnormalities as follows:
Squamous cell abnormalities
- Atypical squamous cells (ASC)
- Atypical squamous cells of undetermined significance (ASC-US)
- Atypical squamous cells, cannot exclude high-grade squamous intraepithelial lesion (ASC-H)
- Low-grade squamous intraepithelial lesion (LSIL), encompasses those previously classified as koilocytic atypia (HPV changes) or cervical intraepithelial neoplasia (CIN) 1
- High-grade squamous intraepithelial lesion (HSIL), encompasses those formerly called CIN 2 or CIN 3
- Squamous cell carcinoma.
Glandular cell abnormalities
- Atypical glandular cells (AGC)
- Atypical glandular cells, favor neoplastic
- Endocervical adenocarcinoma in situ (AIS)
The Bethesda System classifies LSIL and HSIL as squamous cervical precursor lesions.
Although originally used as cytologic diagnoses, the squamous intraepithelial lesion terminology can be used for histologic classification as well.
Generally, CIN grades 1 to 3 are used to classify histologic diagnoses. More than two-thirds of smears showing cellular atypia do not meet diagnostic criteria for dysplasia and are classified as ASC-US or as ASC-H.
Studies have shown that up to 90% of lower-grade Pap tests (LSIL) will spontaneously regress.
However, some estimates suggest LSIL may carry up to a 33% risk of harboring a higher-grade lesion (CIN 2 or 3). HSIL carries a risk of >70%.