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Major Update to Widely Used Classification System of Pap Test Results (dateline August 24, 2002)

The National Cancer Institute has announced a thorough update to the system used to classify Pap test results in more than 90% of laboratories across the United States as well as in several other countries. The 2001 Bethesda System is the result of a workshop convened by the National Cancer Institute in Spring 2001 that included over 400 medical experts representing 20 countries. The group used an Internet bulletin board with over 1,000 comments from health professionals to discuss issues and make recommendations. The 2001 Bethesda System represents the first detailed update to Pap test interpretation guidelines since 1991.

A Pap test (also called a Pap smear) is a screening procedure used to examine cells from the cervix and the vagina. Cervical and vaginal cells are studied to determine whether there is evidence of cancer or pre-cancerous changes. If abnormal cells are found, they are classified according to their degree of abnormality. An estimated 50 million Pap tests are performed each year in the United States, and 3.5 million of those tests produce abnormal results. Most abnormal Pap tests are caused by cervical infections or inflammation which can usually be successfully treated before leading to cancer.

The update to the Bethesda system resulted from improved understanding of cervical cancer and screening practices over the past decade. A report of the updated system by lead author Diane Solomon, MD of the National Cancer Institute and colleagues appeared in the April 24, 2002 issue of the Journal of the American Medical Association.

Significant changes to the system include:

  • Sample adequacy: While the 1991 Bethesda System included information about adequate cervical tissue sample sizes, the 2001 update includes guidelines about the new liquid-based Pap tests (e.g., the "ThinPrep") now used by many physicians.
  • New term of classification (ASC-H): The 1991 Bethesda System used the term ASC-US (atypical squamous cells of undetermined significance) to classify all cervical cells that were not normal but not clearly pre-cancerous. The 2001 Bethesda System includes a category called ASC-H (atypical squamous cells - cannot exclude a high-grade lesion) to help physicians better classify and treat pre-cancerous cervical abnormalities. Another term, "atypical squamous cells favor reactive," is no longer included in the system.
  • Classifying benign cellular changes as "negative:" The 1991 Bethesda System used the category "benign cellular changes" to indicate several different benign (non-cancerous) findings. However, this term caused confusion among physicians, who were unsure whether it was being used to indicate findings that needed further follow-up or findings that were truly "negative." The 2001 Bethesda System includes a category specifically for "negative" benign cellular changes.
  • Computerized results: The 2001 Bethesda System recommends that laboratories report the use of computerized scanning of Pap test slides and the results of molecular testing, such as tests for the sexually transmitted human papillomavirus, HPV.

While the 2001 Bethesda system does not include information on how to evaluate women with abnormal Pap test results, the report was published alongside another paper (the American Society for Colposcopy and Cervical Pathology Consensus Guidelines) that addressed this issue. "Together, Bethesda 2001 and the American Society for Colposcopy and Cervical Pathology guidelines should provide more uniform, evidence-based care of women with cervical abnormalities," said Diane Solomon, MD, the coordinator of the Bethesda System 2001 at the National Cancer Institute (NCI), as quoted in an NCI news release.

Additional Resources and References

  • The report, "The 2001 Bethesda System: Terminology for Reporting Results of Cervical Cytology, Journal of the American Medical Association," is published in the April 24, 2002 issue of the Journal of the Medical Association,
  • To read about the American Society for Colposcopy and Cervical Pathology Consensus Guidelines for evaluating women with abnormal Pap test results, please visit (link to companion article)
  • To learn more about Pap tests, please visit
  • To learn more about cervical cancer, please visit