The Worthlessness of Full-Body Scanning
As seen in this Metafilter post asking for what to spend $3,000 of a Flexible Savings Account on come a couple of responses that illustrate your favorite and mine… statistics! (I’m kidding. But if you need evidence that it’s difficult for everyday people to make informed health care choices, look no further than that post.)
Here’s the problem with medicine: our tests are not perfect. They mess up sometimes. Granted, we try to choose the best tests so that they (or we) mess up less often, but it’s inevitable in some cases. So a test that looks for colon cancer may every so often tell someone they’re normal when they actually have colon cancer. Or a test to decide if someone has HIV may tell someone they have it when they really don’t. There are more benign examples, but these illustrate why us medical folk are so obsessed with data.
And here’s where doctors come in: they have to interpret the tests. I’m simplifying it, but doctors basically take their current suspicion that you have a disease, and then use a test to make them more likely to believe you have a disease, or less likely that you have a disease. Take me: I’m a pretty healthy 25 year-old. If I come to the doctor and say I’m having a heart attack, he’s probably not going to believe me. He’ll do a test, maybe just to make sure (an EKG?), but even if it’s positive, he probably still won’t believe me. Sure it’s possible, but the odds that a healthy 25 year-old is having a heart attack are so low that it’s much more likely that it’s some other disease I have. (If I were a 60 year-old diabetic obese man with high cholesterol and smoked 3 packs a day for 40 years, however, the doctor might be a bit more concerned.)
Now if that made sense (it’s hard to explain it without getting into numbers, which scare me), you’ll understand why getting a full-body CT or MRI scan is pretty pointless. Or even a “treadmill test,” as another poster recommends. If you’re totally asymptomatic and healthy, and don’t have any risk factors for diseases, even if there’s an abnormal little speck on an MRI, your doctor probably won’t be too concerned, because odds are, it’s probably nothing. There’s a term for these specks or masses–incidentalomas–because they’re found incidentally, and usually turn out to be nothing. A ton of us have them–in our pituitary, our thyroid, our adrenal glands–anywhere. The problem is that once you find one of these, often you want to figure out if it truly is benign (usually it’s nothing), and this causes a ton of anxiety, worrying, and health care spending as a result.
If you’re interested, these test qualities are known as the “positive predictive value” or the “negative predictive value.”
We really used to make decisions on odds. We all believed that we can save some source in this way. What else can we depend on in the first sight with a patient?
I totally understand, and seen it. Sometimes it’s all about Epidemiology — BuT wHaT aBoUt wHeN tHe CaSe BrEaKeS wItH wHaT EPIDEMIOLOGY sAyS????? Seen that as well. Then, I thank God then for the many resources… Imaging, lab tests, the development of the “critical eye,” even gut feeling, and so on… We can’t rely on merely one thing. I guess situations like the ones you describe are further proof that nothing is absoulutely absolute in Medicine…
a “positive predictive value” was found in yours truly’s varicella titer – 25 years ago. No sign of disease yet. Good to know, I suppose, but I’m glad these indicators are only “predictive”, either positively or negatively, and generally not acted upon.
Thanks for the great website.
I wouldn’t be too worried, R. Varicella is the virus that causes chicken pox. And while these values are only predictive, they often *are* acted upon. While sometimes we can’t say for sure someone has a disease, often if we get a test that agrees with our suspicion for a disease, we will act upon it and treat.
Hmmm…have a case where patient (50 year old) is overweight, complain of chest pain, shortness of breath (sometimes) and neck pain (suspected of high blood pressure). I recommended him to ge a blood test done and see a cardiologist. results out in 2 weeks shows LDL and HDL level totally normal, sugar level normal, pass the treadmill test. doctor says he’s perfectly healthy and the chest pains and neck pain are due to stress in work and aging. the patient came back to me and ask what should he do next (he really feels that something in his body is not right and he wants to know what it is). My Senior Pharmacist suggested him to consult another doc (I’m not sure if it’s the right thing to do). Another question: Blood test for LDL and HDL – are they acurrate??