The recent media coverage of false negative pap smears has brought concern from some patients over their test results. Just how accurate are pap smears?

It was 1928 when George N. Papanicolaou discovered that cellular changes in the genital tract of guinea pigs could be used to predict which of the animals would get cancer. It was years later when this was recognized as a useful screening test for cancer in humans.

The pap smear is not perfect. Even at a good lab there is a 5-10% false negative rate. Fortunately, there is usually a lag time of several years between the pre-cancerous cervical changes that can be detected on a pap smear and invasive cancer of the cervix which can follow. This is why pap smears are done on a yearly basis by many Gynecologists. This allows any false negatives to be repeated in a year, be re-examined by the lab, and be correctly diagnosed.

The recent problems with paps, like so many of the problems in medicine today, are related to cost. The labs doing these paps were paying the cytotechnologists, who read the paps, by the slide, and not by the hour. This encouraged speed and not accuracy. Also, a Pathologist M.D. was not always in the lab to answer questions. Some of these labs were apparently even allowing slides to be taken home to be read! This all led to 25-35% incorrect results. These labs were less expensive, but the saying "You get what you pay for" applies in medicine, too.

The lab we use is certified by the College of American Pathologists, which requires a biannual inspection. The director of the cytology lab has had additional training in cytology. Questions from the techs are encouraged and a certain percentage of slides are automatically re-read to add to the quality control. The cytotechs are paid by the hour and periodically receive continuing education.

We also use a new liquid based pap that is not a smear. The cells are put in a solution and sprayed on the slide. This prevents the cells from being piled up on the slide and also removes bacteria and cervical mucus that can obscure the appearance of the cells and cause errors in interpretation. We also now check for human papilloma virus (HPV) when we get certain results back. This prevents unnecessary follow-up.

The pap smear is not perfect, but, if it is done by a good lab in conjunction with yearly Gynecologic follow-up, it can markedly reduce your risk of being found to have an inoperable cervical cancer.


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