Papanicolaou (Pap) Test: Purpose and Recommended Frequency
The Papanicolaou (Pap) test is a screening tool designed to detect precancerous and cancerous cells in the cervix, with recommended screening beginning at age 21 regardless of sexual activity history, and continuing at specific intervals based on age and risk factors. 1
Purpose of the Pap Test
- The Pap test is designed for early detection of cervical cancer and its precursor lesions, making it one of the most effective and cost-effective cancer screening methods available 2, 3
- Since its introduction in 1941, the Pap test has significantly reduced the incidence and mortality rates of squamous cell carcinoma of the cervix in areas with well-established screening programs 4
- The test detects precancerous changes that are not visible to the naked eye by sampling cells from the cervix, allowing for early intervention before cancer develops 4
- The primary cause of cervical cancer is persistent human papillomavirus (HPV) infection, with HPV detected in 99% of cervical tumors, particularly oncogenic subtypes such as HPV 16 and 18 2
Recommended Screening Frequency
Age-Based Recommendations
- Ages under 21: Screening is not recommended regardless of sexual activity history 1, 2
- Ages 21-29: Screening should be performed every 3 years with Pap tests alone 1, 2
- Ages 30-65: The preferred approach is screening every 5 years with both HPV test and Pap test (co-testing), or every 3 years with Pap test alone 1, 2
- Ages over 65: Women can discontinue screening if they have had adequate prior normal screening results and are not at high risk for cervical cancer 1, 2
Special Considerations
- Women who have had a total hysterectomy (including removal of the cervix) for non-cancerous reasons and have no history of high-grade precancerous lesions can discontinue screening 2
- Women with HIV infection should receive more frequent screening due to their 10-11 times higher likelihood of presenting with abnormal cervical cytology compared to the general female population 5
- Women who have been vaccinated against HPV should still follow the same screening guidelines as unvaccinated women, as the vaccines do not protect against all oncogenic HPV types 2
Interpretation and Management of Results
- Results are reported using the Bethesda System, which categorizes findings as normal, atypical squamous cells of undetermined significance (ASC-US), low-grade squamous intraepithelial lesion (LSIL), high-grade squamous intraepithelial lesion (HSIL), or atypical glandular cells (AGC) 5
- Approximately 5% of Pap tests will show abnormal results, requiring appropriate follow-up 3
- HPV DNA testing has revolutionized the management of abnormal Pap results, particularly for women with ASC-US, where it helps determine which patients need colposcopy 5, 6
- Women with LSIL or HSIL should be referred for colposcopy with directed biopsy 5
Clinical Importance
- The Pap test has decreased both the incidence and mortality of cervical cancer in areas with well-established screening programs 2
- When combined with HPV testing, cervical screening provides 60-70% greater protection against invasive cervical cancer compared with cytology-based screening alone 2
- Despite its effectiveness, the Pap test has limitations, including a false-negative rate of at least 5% even in the best laboratories 7
- Regular screening according to guidelines is crucial, as approximately half of women diagnosed with cervical cancer in the United States had not had a Pap test in the 3 years before diagnosis 2
Common Pitfalls to Avoid
- Over-screening women under 21 years or screening more frequently than recommended intervals 1
- Inappropriate use of HPV testing in women under 30 years for primary screening 1
- Failure to adequately sample the transformation zone, resulting in unsatisfactory specimens 1
- Scheduling the test during menstruation, as blood may interfere with interpretation 1
- Misinterpreting the pelvic examination as including a Pap test when no sample was actually collected 2