There is a tremendous amount of effort devoted to cervical cancer screening in the United States. We estimate that 61 million women had at least one Pap smear in 2000. We found that Pap smear screening is common even among elderly women. Most importantly, while it has been more than a decade since most professional societies revised their recommendations for Pap smear screening intervals in favor of less frequent screening, we found that the majority of American women report being screened for cervical cancer annually.
For a number of reasons, it is difficult to quantify how many women are being screened more often than is recommended. Most agree that only women at high risk should be screened annually. Unfortunately, until very recently guidelines have been either remarkably imprecise or remarkably expansive about what constitutes high risk (see ).5,8–10
Some recommend that a woman's decision about annual screening should be “determined by her risk factors.”8
Others recommend annual screening if any one of a number of “high-risk factors” is present—including (among others) herpes infection, any sexually transmitted disease, smoking, and having had a partner who has had multiple partners.10
Because it would be nonsensical to argue that the majority of American women is at higher than average risk, however, there seems little doubt that excessive screening is occurring. Were one to assume that one-fifth of the population was at high risk, our data would suggest that 25 million women currently undergoing annual screening are being screened more often than necessary. Assuming 10% of women were at high risk, the figure would rise to 33 million undergoing unnecessarily frequent screening.
Professional Medical Society Guidelines for Pap Smear Screening Intervals
While observational data suggest that Pap smear screening has substantially reduced cervical cancer incidence and mortality, the same data also suggest that annual screening provides little, if any, benefit over triennial screening. In 1986, the World Health Organization's International Agency for Research on Cancer concluded, after analyzing evidence from large-scale screening programs in 8 countries, that annual screening confers a trivial, if any, advantage compared with triennial screening in reducing the incidence of cervical cancer.1
Similarly, a recent U.S. study found that rates of high-grade cytologic abnormalities did not differ among women who waited 1, 2, or 3 years after a normal Pap smear to get their next test.19
In another study, investigators found extremely low rates of histologic abnormalities in the next 2 annual Pap smears after a normal smear.20
Based upon these studies, the CDC recently concluded that annual screening shows no clear advantage over less frequent screening, and may even lead to worse health outcomes due to a greater number of questionable abnormalities requiring intervention.21
In fact, it is not difficult to recognize the potential disadvantages of annual compared with triennial screening. First, more frequent Pap smear testing means more Pap smears must be interpreted. Millions of additional Pap smears place enormous demands on the limited supply of the human resource required for smear interpretation—cytotechnologists.22
Concerns that overworked cytotechnologists were responsible for unacceptably high rates of inaccurate Pap smear readings prompted the federal government in 1988 to enact legislation mandating strict laboratory standards (Clinical Laboratory Improvement Amendments of 1988) that included a requirement that technologists examine no more than 100 smears each day.23,24
Considering that each smear contains between 50,000 and 300,000 cells, even this is an ambitious task.25
Reducing the amount of annual screening among average-risk women (and stopping screening among women who have had a hysterectomy) would decrease the annual workload for cytotechnologists by millions of Pap smears per year, allowing more time for smear review, mandatory slide rescreening, and improved quality assurance.
Second, more Pap smears interpreted means more abnormal Pap results. Each year an estimated 3.1 million Pap smears in the United States (5% of smears) are read as abnormal. Our data show that 20% of American women have had at least one abnormal smear. Investigators have found elevated levels of anxiety, distress, and negative self-image in women with abnormal smear results,26
with high levels of anxiety persisting during surveillance for mild smear abnormalities.27
Furthermore, most abnormal smear results are either atypical squamous cells of undetermined significance (comprising 60% of abnormal smears) or low-grade squamous intraepithelial lesions (33% of abnormal smears),28
the majority of which are transient lesions that would resolve spontaneously without treatment.29–31
This raises obvious questions about the benefit of promptly identifying such lesions.
Third, more abnormal results mean more follow-up procedures, including a substantial amount of testing and treatment of transient lesions. The volume of follow-up Pap smears is difficult to estimate, but our data suggest that the large majority (90%) of women with an abnormal Pap smear have one or more follow-up smears or additional tests. Many women will also undergo more invasive testing and treatment. In Australia, where national screening policy consists of routine biennial smears, 2.5% of women undergo colposcopy each year, and the lifetime risk of colposcopy for a 15-year-old woman is estimated to be 77%.32
Our study has several limitations. First, there may be legitimate concerns about our process for estimating screening intervals, which involves several assumptions. Our assumption of a single discrete screening interval for each woman is somewhat artificial, but unlikely to lead to an overestimate of screening frequency. We also implicitly assumed that each woman's Pap smears over the previous 6 years had been regularly spaced, allowing us to generalize the number of smears during that period into a periodic screening frequency. However, because we were able to stratify our analysis according to history of abnormal Pap smears, we were able to effectively eliminate the possibility that additional follow-up Pap smears artificially inflated our estimate of screening frequency among the 80% of women with no prior abnormal smears.
Second, our estimates of screening frequency are based on self-reports, which are likely to differ from actual screening history. Several studies have documented that women's self-reports of Pap smear testing consistently tend to overestimate screening.33–38
Overreporting of screening has only been demonstrated with respect to questions about timing of the most recent Pap smear. There are no data about the accuracy of self-report of the number of tests in a given time period. To the extent that women did overestimate the number of Pap smears in the past 6 years, we may have overestimated the amount of annual screening. As is the case with all survey-based research, the generalizability of our estimates is also limited by survey nonresponse. If nonresponders undergo screening less often than responders, we may have overestimated the screening frequency of American women. Our response rate of 72%, however, compares favorably with rates from other national surveys. Certainly, claims-based analysis of Pap smear screening patterns and intervals would have yielded more accurate estimates of actual practice. However, a claims-based analysis including a sample representative of civilian noninstitutionalized American women, as is included in NHIS, is not possible. In fact, ours are the first national estimates of Pap smear screening frequency.
Annual screening may be a difficult habit to break. Studies of physicians’ preferences have found that, despite professional society guidelines endorsing less frequent screening, nearly all obstetricians/gynecologists and the large majority of primary care physicians recommend annual Pap smear screening for their female patients of all ages.39
It is therefore not surprising that, of women surveyed after a revision of their HMO's Pap smear screening guideline from annual to triennial screening, the majority were skeptical or negative regarding the change, particularly those with a personal history of frequent (annual) Pap smears.40
It may be appropriate to continue annual Pap smear screening in particularly risk-averse women, as well as women at high risk for cervical cancer. However, many women may be comfortable with, indeed prefer, less frequent screening. In fact, 30% of women in the HMO survey were neutral or viewed the decrease in screening frequency favorably.40
If physicians were to recognize and discuss with patients the comparable benefits of annual and triennial screening, giving average-risk women “permission” to be screened every 2 or 3 years, many women might gladly forego annual screening, allowing time for discussion of other important preventive health issues during annual visits.
There is increasing awareness that health care priorities must be redirected away from unnecessarily frequent cervical cancer screening. The National Breast and Cervical Cancer Early Detection Program (a federal program promoting breast and cervical cancer screening among low-income and uninsured women) recently reexamined their own policy. They now require participating sites to direct more resources to women with no prior (or remote) cervical cancer screening, and to discontinue the practice of annual screening in women who have had 3 normal annual Pap smears.41
Even as screening technology and test accuracy evolve in the coming years42
with improvements in liquid-based slide preparation, automated microscopy, and human papillomavirus testing, the question of how often to test for cervical cancer and its precursors will only increase in importance. Based on our findings, we recommend that health care providers discuss screening recommendations and rationale with their female patients, and offer Pap smear screening every 2 or 3 years for women who are not at high risk of cervical cancer.