PHILADELPHIA—“Litigation is killing the Pap test. You have to allow patients to sue, but suing because the test is imperfect, we can’t allow,” Richard M. DeMay, MD, told Oncology News International. The solution, he believes, is “some sort of legislation.”
Dr. DeMay discussed this issue at a symposium conducted at the annual fall meeting of the American Society of Clinical Pathologists and College of American Pathologists. Dr. DeMay is professor of clinical pathology and director of cytopathology, University of Chicago.
“No test ever invented has been as successful as the Pap smear in preventing cancer, but it is not a perfect test,” Dr. DeMay said. And, he believes, cytologists are being held to an impossible standard of perfection in malpractice litigation.
Although a false-negative rate of 5% to 10% may be an admirable goal, a more realistic standard, he said, would be below 15% to 20%. “Cytological errors should be judged in the context of overall laboratory performance. Otherwise, we have a zero-error standard by default,” he said, adding that malpractice judgments for false-negative Pap smears can cost as much as $750,000 each.
Sampling errors account for a significant number of false-negative cases, he said, and diagnostic errors occur in even the finest cytology laboratories. “No cytology laboratory, no matter how well run, is completely free of diagnostic errors,” he said, “the most important being false negatives.”
These, he reported, occur at a low “but well documented and probably irreducible” rate of at least 5% to 10%. “One of every 10 to 20 positive smears will be missed in routine screening,” he said.
Looking at this statistic from the more optimistic “glass being mostly full” point of view, instead of “glass being slightly empty,” he said, “this means that using a simple, ordinary Pap smear, we can detect as many as 90% to 95% of significant lesions. If we were to grade this test, it would get an A.”
A Victim of its Own Success?
In a way, the Pap smear has been a victim of its own success, Dr. DeMay said. This is because as the prevalence of a disease falls, the accuracy, or predictive value, of any diagnostic test for the disease, is diminished.
This effect, he continued, is independent of the sensitivity and specificity of the test itself. “In other words, you can do the same good job you always did, but if there are fewer cases of the disease, your diagnostic accuracy goes down.”
Over the last several decades, he said, the Pap smear has proven remarkably effective in reducing the incidence of invasive cervical cancer. “Therefore, if it ain’t broke, we should be very careful what we do to ‘fix’ the perceived problems with the Pap smear,” he warned.
Well-intentioned efforts to improve the Pap smear, he said, may have the unintended and paradoxical effect of increasing the number of cases of cervical cancer by raising costs and thus decreasing access to this life-saving test. “There is a real danger that we will make the Pap smear so good that no one will be able to afford it,” he quipped.
The $100 Pap smear may soon become a reality, he believes, a figure that includes the cost of thin-layer preparation, computer rescreening, compliance with government regulations, and malpractice insurance. “Loss of the inexpensive, widely available Pap smear would undoubtedly lead to increased cervical carcinoma rates,” he concluded.
