Stacie Chapman’s heart skipped when she answered the phone at home and her doctor — rather than a nurse — was on the line. More worrisome was the doctor’s gentle tone as she asked, “Where are you?”
On that spring day in 2013, Dr. Jayme Sloan had bad news for Chapman, who was nearly three months pregnant. Her unborn child had tested positive for Edwards syndrome, a genetic condition associated with severe birth defects. If her baby — a boy, the screening test had shown — was born alive, he probably would not live long.
Sloan explained that the test — MaterniT21 PLUS — has a 99 percent detection rate. Though Sloan offered additional testing to confirm the result, a distraught Chapman said she wanted to terminate the pregnancy immediately.
The test may have a 99% detection rate — if the fetus has a trisomy, there’s a 99% chance it will be picked up by the test — but what also matters here is the false positive rate. How often does the test say the fetus is trisomic when it’s normal and healthy? They don’t say.
The companies marketing these tests are overselling their virtues, and some of the medical professionals recommending abortions after positive results don’t seem to understand the concept of false positives, which is shocking.
Another standard example of a test made useless by a high false positive rate is the Prostate-Specific Antigen (PSA) test, which isn’t even recommended for routine screening any more — too many healthy men were getting flagged by the test as potentially carrying prostate cancer, and were then given biopsies or even surgery.
The PSA test may give false-positive or false-negative results. A false-positive test result occurs when a man’s PSA level is elevated but no cancer is actually present. A false-positive test result may create anxiety for a man and his family and lead to additional medical procedures, such as a prostate biopsy, that can be harmful. Possible side effects of biopsies include serious infections, pain, and bleeding.
Most men with an elevated PSA level turn out not to have prostate cancer; only about 25 percent of men who have a prostate biopsy due to an elevated PSA level actually have prostate cancer.
Only 25%! That means that if you get a positive PSA test, odds are better that you don’t have prostate cancer than that you do.
That’s bad enough that you’d suffer through a biopsy because of a sloppy test…but imagine if you’d aborted a healthy and wanted fetus because a test was that useless.