The Bethesda system (TBS)

The Bethesda system (TBS) of classifying Pap tests was developed by the United States National Cancer Institute (NCI) to provide more detailed information about Pap test results. The system increases the communication between the health professional who does the Pap test and the laboratory specialist (cytologist) who examines the cervical cells. It provides information about the quality of the cell sample and the types of cell changes found.

The Bethesda system of reporting Pap test results consists of three main parts.1

Part 1: Sample suitability

The Pap smear will be described as:

  • Satisfactory for evaluation.
  • Unsatisfactory for evaluation. A reason will be given for the inability to evaluate the cell sample, such as too few cells collected.

Part 2: General categorization (optional)

To indicate whether the cells collected were normal or abnormal, the cells may be described as:

  • Negative for intraepithelial lesion or cancer (malignancy).
  • Epithelial cell abnormality.
  • Other, such as endometrial cells found.

Further information from the descriptive diagnosis section will be included in these category results.

Part 3: Descriptive diagnosis when there is an abnormality found on the Pap smear

Some abnormal cell changes are described as:

  • Negative for intraepithelial lesion or cancer (malignancy). These changes can be caused by:
  • Epithelial cell abnormalities.
    1. Squamous cell
      • Atypical squamous cells (ASC): This category is used for minor cell changes due to unknown causes. ASC is divided into two types:
        • ASC of undetermined significance (ASC-US).
        • ASC that cannot exclude high-grade squamous intraepithelial lesion (HSIL) (ASC-H).
      • Low-grade squamous intraepithelial lesions (LSIL): This category is used for cells that show definite minor changes but are unlikely to progress to cancer. This category includes presence of human papillomavirus (HPV) infection, mild dysplasia, and cervical intraepithelial neoplasia (CIN 1).
      • High-grade squamous intraepithelial lesions (HSIL): This category is used for cell changes that have a higher likelihood of progressing to cancer. This category includes the presence of moderate to severe dysplasia, carcinoma in situ (CIS), CIN 2 and CIN 3, or changes suspicious for invasive cancer.
      • Squamous cell invasive cancer.
    2. Glandular cell abnormalities
      • Atypical glandular cells (ACG) include:
        • Endocervical (from cervical canal) cells.
        • Endometrial cells. These cells are normally found in the uterus. Their presence in the cervix might occur in menstruating women but would be abnormal in postmenopausal women not on hormone replacement therapy.
        • Glandular cells.
      • Atypical glandular cells, favor cell growth (neoplastic changes):
        • Endocervical cells
        • Glandular cells
      • Endocervical adenocarcinoma in situ (AIS)
      • Adenocarcinoma:
        • Endocervical
        • Endometrial
        • Extrauterine
        • Other, not specified


  1. National Cancer Institute (2001). Bethesda System 2001. Available online:

Last Updated: January 5, 2009

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