Since widespread screening for cervical cancer with the Pap test began in the United States, cervical cancer rates declined from 14 per 100,000 women in 1973 to 8 per 100,000 in 1994. Nevertheless, cervical cancer is still the ninth leading cause of cancer deaths among U.S. women, and some of these women had recently received negative Pap test results, which obviously were incorrect (false-negative).
About two-thirds of false-negative Pap test results are caused by sampling error (abnormal cells are not collected or are not transferred to the Pap slide) or detection error (abnormal cells on the Pap slide are missed or misinterpreted). New methods to correct these errors have been introduced, such as monolayer cytology and computer screening or rescreening.
A recent review of studies that compared conventional and newer Pap tests with a current reference standard (histologic examination, colposcopy, or cytology) found that conventional Pap tests were only moderately accurate and did not achieve concurrently high sensitivity and specificity. Estimates of sensitivity and specificity varied greatly (ranging from 30 to 87 percent and 86 to 100 percent, respectively) in individual studies. Nevertheless, serial Pap testing remains effective. Pap testing every 3 to 5 years will probably detect abnormalities missed in one screening because cervical cancer is usually a slow-growing disease, and many low-grade lesions regress spontaneously.
There were insufficient high-quality data to estimate the accuracy of new cytologic methods for cervical screening, such as thin-layer cytology (ThinPrep), the computerized rescreening device (PAPNET), and the algorithmic classifier (AutoPap), all of which have been approved by the U.S. Food and Drug Administration. These results are based on an evidence report prepared by the Duke University Evidence-based Practice Center (EPC), which is directed by David B. Matchar, M.D., and supported by the Agency for Healthcare Research and Quality (contract 290-97-0014).
See "Accuracy of the Papanicolaou test in screening for and follow-up of cervical cytologic abnormalities: A systematic review," by Kavita Nanda, M.D., Douglas C. McCrory, M.D., M.H.Sc., Evan R. Myers, M.D., M.P.H., and others, in the May 16, 2000 Annals of Internal Medicine 132, pp. 810-819.
Editor's Note: This journal article is drawn from the evidence report, Evaluation of Cervical Cytology (AHRQ Publication No. 99-E010). Copies of the full report and summary of the report (AHRQ Publication No. 99-E009) are available from the AHRQ Publications Clearinghouse.