Unfortunately, the Pap smear is not perfect. The failure to detect cervical abnormalities prior to the development of cancer may be related to poor sampling, errors in Pap smear interpretation and lack of patient/clinician follow-up. Ironically, the majority of failures are due not to Pap smear errors but rather the lack of Pap smear testing entirely. Furthermore, in those women who do have Pap smear testing, most diagnostic failures are related to sampling error.

Diagnostic interpretive errors do occur at a low, but well-documented, and probably irreducible rate of at least 5 to 10 percent of all positive cases. Because over 90 percent of all smears are negative, false negatives represent no more than 1 to 2 percent of all smears. Pap smear screening requires a tremendous amount of sustained concentration with subjective interpretation of sometimes extremely subtle abnormalities. Even the most highly qualified and experienced cytotechnologists will occasionally miss subtle abnormalities. For this reason, our current quality assurance measures at Dynacare Laboratories go beyond the regulatory requirements in an effort to reduce errors to an absolute minimum.

We are cautiously optimistic that new technologies will improve this already excellent test. Two companies have recently received FDA approval for automated instrument rescreening of Pap smears originally interpreted as negative by cytotechnologists.

The Auto Pap 300 QC (Neopath-Inc., Redmond, WA) is an automated, computerized instrument which scans the conventional pap smear using a high-speed video microscope with image interpretation software to classify smears as to their likelihood of having abnormal cells. Those smears which are classified as most likely to have abnormalities-nalities are then screened and evaluated once again by cytotechnologists in the conventional manner.

A similar approach by Papnet (Neuromedical Systems, Inc., Suffern, NY) also scans the conventional smear with a video microscope and 128 high resolution images of the most abnormal cells are stored and available for review on a high-resolution video screen. The slides judged to possibly contain abnormal cells based on the video images are then referred for a second microscopic review by cytotechnologists in the conventional manner.

Neither of these technologies have been approved for primary screening of Pap smears and can only be used as a second screen following a cytotechnologist's initial review. The goal of these technologies is to identify smears requiring a second human review in the conventional manner. For this reason, these .technologies may add little value if smears are routinely double-screened by cytotechnologists in a quality laboratory. At Dynacare Laboratories, double screening (re- screening) is routinely performed on between 10 and 15 percent of negative smears. However, rescreening can be performed on any smear upon request, and all high risk patient smears are either referred to a pathologist for evaluation after initial screening, or re-screened by our most experienced cytotechnologists.

Another type of technology which has received FDA approval for use in gynecologic cytopathology is the Thin-prep 2000 (Cytyc Corp., Boxborough, MA). With this system, cells swabbed from the cervix and endocervix, instead of being smeared onto a glass slide, are put into a fluid-filled vial which is then used to make slides with a thin layer of cells for microscopic evaluation. The slides are then screened and interpreted in the usual manner by cytotechnologists. This technology has been shown to significantly decrease the incidence of unsatisfactory samples and samples which are satisfactory but limited for evaluation. The detection of abnormal cells using thin prep technology appears to be as good or better than conventional smears. However, the cost is considerably more.

Although we are hopeful that these technologies will improve the current Pap smear screening trials in sharply defined laboratory environments or patient populations where personnel and cost related factors may not reflect actual practice conditions.

The American Society of Cytopathology has urged its membership to proceed with caution in the adoption of these technologies and has reiterated that the single most important step that the public can take to lower the risk of cervical cancer is regular cervicovaginal (Pap) smear examination performed by accredited cytopathology laboratories dedicated to the highest standard of practice. In the August 1996 newsletter of the American College of Obstetricians and Gynecologists, a wait-and-see attitude was urged. Our responsibility in the meantime is to undertake critical analysis of the relevant literature and current articles.

During this period of evaluation we realize that some clinicians and/or patients may desire further testing by automated instrumentation or thin prep technology. Dynacare Laboratories will make every effort to meet these requests on an individual basis although we cannot recommend any additional testing or changes in the conventional Pap smear at this time.

This article was prepared by Ronald J. Tickman, MD.

After initial cytotechnologist screening approximate smears are reviewed by pathologists based on previous history or abnormality on the smear. These cases may also require interdepartmental consultation and account for the majority of reporting is delayed beyond 72 hours. Some cases may be delayed due to incomplete clinical information such as source of the smear, LMP or hormonal history. Although it is most efficient to to handle cases in a consecutive, first in first out manner, if the clinical situation requires an expedited result, this can be accommodated by calling our Cytology Laboratory at (206) 386-2893.

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