Submitted by Dr. Ankeney for Kaiser Permanente
Did you know that every medical test presents risk? I’m talking about scans, blood draws, even biopsies. To some it’s a counterintuitive reality, but medical testing has drawbacks.
Yikes. This isn’t a fun thing to ponder. What kind of risks are we talking about? Here’s an example: Obtaining an MRI or CT in low-risk populations frequently detect benign abnormalities (sometimes jokingly referred to as “incidentalomas”) that would never have caused harm if they weren’t detected. Worse, they can at times return false positive findings – saying something problematic is there when it isn’t – which usually generates major anxiety while also wasting money. Often that imaging prompts avoidable or even hazardous surgery, sometimes with needless additional exposure to radiation.
Take MRI for migraines. Physicians rarely find a single brain tumor in 100+ patients who get MRIs for chronic headaches. Experts suggest patients undergo imaging for migraines only in very rare cases. But studies show that nearly half of patients with headaches eventually get an MRI.
All medical tests are measured for their potential to generate false positives (saying there’s a problem when there isn’t one). They’re also measured for the chances of generating false negatives (missing a problem that is actually there). Many tests are good at one part of that but not so good at the other.
Take the Prostate-specific Antigen (PSA) test, used to try to detect prostate cancer. PSA is a protein secreted by cells in the prostate gland and is one component of ejaculate. It is present in small quantities in the blood of men with healthy prostates but is often (not always) elevated in prostate cancer.
Prostate cancer screening using the PSA test first started in the 1980’s. Since that time, prostate cancer diagnoses increased from 1 in 11, to 1 in 6. This sounds like a good thing, but there’s more to the story. Turns out the risk of dying from prostate cancer hasn’t changed at all. It’s stubbornly stuck at 1 in 34. Furthermore, studies suggest that somewhere between 23-50 percent of prostate cancers were over diagnosed.
Interesting word, “over diagnosed.” What does it mean? It’s the detection by screening of a condition that would never have caused symptoms in a patient’s lifetime. As described above, overdiagnosis leads to all kinds of things that paradoxically harm us, rather than help.
Let’s return to the PSA test. It has a false negative rate of only about 10 percent. This means that if the test comes back negative, there is a nearly 90 percent chance it’s correct and there is no cancer in the prostate. But the test does poorly at avoiding false positives. In those who test positive for cancer via the PSA, nearly 80 percent of them won’t actually have a problem (either because there isn’t really cancer there, or the cancer that is there isn’t a dangerous type). That’s a lot of people walking around thinking they probably have a terrible disease when they don’t.
So we’re left with a situation where medical tests can be helpful, but not always. This is where a good medical provider can be so helpful. Modern medical decision making is a balancing act between risks and benefits. There is rarely absolute certainty in our use of medical technology. So as you think about these things, lean on your doc to help guide you through this wilderness of data and risk. It’s why we’re here.
