A 'Phantom' Diagnosis With Real Consequences
False positives in medicine are as common as the common cold.
The discovery of a false positive is usually good news. The patient doesn't have a dread disease or malignancy. But false positives have also led to serious consequences, such as needless amputations, hysterectomies, and other painful procedures, plus emotional trauma and medical regimens that can permanently affect patients' lives.
How patients react to false positives can be drastic and life-altering. Erroneous tests showing the presence of sexually transmitted diseases, for example, have caused ostracism, the breakup of families, and even gunplay. After being mistakenly told that they're terminally ill, some patients have quit their jobs, given away their life savings, and put their pets to sleep.
Physicians can act to protect their patients, and themselves, from an erroneous diagnosis. There are ways to minimize the injury, pain, and likelihood of litigation from false positives, say patient safety experts.
The Prevalence of False Positives
The number of misdiagnoses due to false positives may be much larger than previously thought, say medical researchers.
National expenditures for false-positive mammograms and breast cancer overdiagnoses alone are estimated at $4 billion a year, according to a report in the April 2015 issue of Health Affairs. The study reviewed spending data from more than 702,000 female patients aged 40-59 who are covered by health insurance.
Mammograms are being overinterpreted as suspicious for breast cancer approximately 11% of the time, the report found, affecting nearly 3.2 million patients per year. As such, the authors recommended that specialty societies revise existing guidelines regarding the age when patients should begin receiving regular mammograms.
An earlier study by the National Institutes of Health reviewed the records of 68,436 patients, aged 55-74 years, who participated in a clinical trial of prostate, lung, colorectal, and ovarian cancer screening. The goal was to determine the cumulative risk of a false positive and the resulting risk of a diagnostic procedure.
The conclusion was startling. "For an individual in a multimodal cancer screening trial, the risk of a false-positive finding is about 50% or greater by the 14th test. ... The cumulative risk after 14 tests of undergoing an invasive diagnostic procedure prompted by a false-positive test is 28.5% (CI, 27.8%-29.3%) for men and 22.1% (95% CI, 21.4%-22.7%) for women."
The authors said, "Physicians should educate patients about the likelihood of false positives and resulting diagnostic interventions when counseling about cancer screening."
Sometimes, false positives can be caused by a seemingly unlikely source: tattoo ink. "A 32-year-old woman presented with clinical stage 1B1 cervical cancer and extensive tattoos of the lower extremities," notes a case report in the July 2015 issue of Obstetrics & Gynecology. As the report went on to say, "Preoperative PET-CT scan identified 2 ileac lymph nodes with increased fluorine-18-deoxyglucose uptake suspicious for metastatic cancer. At the time of surgical resection, bilateral pigmented lymph nodes were identified with histologic examination showing deposition of tattoo ink and no malignant cells."
The authors warned, "Physicians should be cognizant of the possible effects of tattoos on PET-CT findings while counseling patients and formulating a treatment program."
The tests for many other diseases may render false positives as well, including tests for hepatitis C, HIV, and many others.
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Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Mark Crane. Malpractice Risk: The Dangers of False Positives - Medscape - Sep 14, 2016.