The American College of Obstetricians and Gynecologists (ACOG) recently published a clinical management guideline on cervical cytology screening. The complete guideline, ACOG Practice Guideline No. 45, appeared in the August 2003 issue of Obstetrics and Gynecology.
Incidence and mortality from cervical cancer have decreased by almost one half since the early 1970s, but the annual rate has remained at approximately eight cases per 100,000 women over the past few years, according to ACOG. In the United States, cervical cancer remains the third most common gynecologic malignancy.
Cervical cytology is inexpensive and readily accepted by American women. Cervical cancer has a long premalignant phase, which allows repeated tests to significantly reduce the impact of individual false-negative test results. For patients with truly positive test results, treatment is effective in reducing the chance of progression to invasive disease.
Errors in Cervical Cytology
Occasionally, cervical cancer is undetected despite a recent screening test because of errors in sampling, interpretation, or follow-up. According to ACOG, sampling and interpretation errors are associated with 30 percent of new cases of cervical cancer each year. Sampling errors occur when dysplastic cells on the cervix are not transferred to the slide; errors of interpretation are attributed to lack of recognition of abnormal cells in the laboratory.
Techniques of Cervical Cytology
ACOG emphasizes that patient preparation and proper provider technique can help optimize the collection of cells:
Cells should be collected before the bimanual examination.
Avoid contaminating the sample with lubricant.
Cell collection for cervical cytology should be done before collection for sexually transmitted diseases.
The entire portio of the cervix should be visible when the sample is obtained.
Routine swabbing of the discharge from the cervix may result in samples of scant cellularity.
The specimen should be transferred and fixed as quickly as possible to reduce air-drying artifact.
The Bethesda System of reporting cervical cytology results is the most widely used system in the United States. The ACOG report highlights a portion of the revised terminology from the 2001 version.
Clinical Considerations and Recommendations
When should screening begin? Annual cervical cytology screening should begin approximately three years after initiation of sexual intercourse, but no later than 21 years of age.
What is the optimal frequency of cervical cytology screening? Annual cytology screening should be recommended for women younger than 30 years. Women 30 years and older who have had three consecutive test results negative for intraepithelial lesions and malignancy may be screened every two to three years. Women with certain risk factors may require more frequent screening, including women infected with human immunodeficiency virus, women who are immunosuppressed, and women who were exposed to diethylstilbestrol in utero. Regardless of the frequency of cervical cytology screening, women should be counseled that annual examinations, including pelvic examination, are still recommended.
When is it appropriate to recommend discontinuing screening? Women who have had a total hysterectomy for benign indications and have no history of high-grade cervical intraepithelial neoplasia (CIN) may discontinue routine screening. Women who have had a total hysterectomy and have a history of CIN 2 or 3, or in whom a negative history cannot be documented, should continue to be screened annually until three consecutive satisfactory negative vaginal cytology results are obtained. A patient who has had three consecutive negative examinations following treatment for CIN 2 or 3 before having a hysterectomy also may discontinue screening. When the cervical cytology and surgical history are not available to the physician, screening recommendations may need to be modified.
How do the various methods of cervical cytology compare in terms of effectiveness? Evidence-based data indicate liquid-based and conventional methods of cervical cytology are acceptable for screening. Physicians should consider the screening history of the patient, cost of the test, and possible effects of false-negative or false-positive results before selecting which method to use.
When is human papillomavirus (HPV) testing appropriate? It is used for the primary triage of cervical cytology tests read as atypical squamous cells of undetermined significance (ASC-US). HPV testing may be done by testing from residual preservative if liquid-based cytology is used or by performing a separate HPV DNA test at the same time as cervical cytology and storing it for use if ASC-US is the result. HPV testing also may be useful in the secondary triage of women with a cytologic diagnosis of ASC-US, atypical squamous cells cannot exclude high-grade squamous intraepithelial lesions (ASC-H), or low-grade squamous intraepithelial lesions (LSIL) in whom colposcopy is negative or biopsy fails to reveal CIN.
When cervical cytology and HPV DNA testing are used together, can women be screened less frequently? The U.S. Food and Drug Administration (FDA) recently has approved the combination of cervical cytology and HPV DNA testing. This combination testing is appropriate for women 30 years and older. Women who receive negative results on both tests should be rescreened no more frequently than every three years. ACOG notes that the FDA approval for use of this approach is only for the panel of high-risk HPV types. Routine testing using cytology alone remains an acceptable screening plan.