Wednesday, June 8, 2016

Why do-it-yourself blood tests are a bad idea

It sounded too good to be true when I first heard about Theranos, a company that promised to revolutionize medical testing by making it possible to perform dozens of tests on a single drop of blood, rather than the several tubes that would typically be required. And that wasn't all. Theranos CEO Elizabeth Holmes, a Stanford dropout and media magnet whose wardrobe seems to consist solely of all-black outfits, promised to empower patients by giving them the ability to order their own tests, rather than needing to ask a doctor to do so. Now that the company is under criminal investigation and under pressure to prove that its technology works, FiveThirtyEight reporter Katherine Hobson pointed out that routine blood testing in healthy people has numerous downsides that Holmes never mentioned, including poor predictive value, false positives, overdiagnosis. Even if the test accurately diagnoses a risk factor such as high blood sugar levels, a United Kingdom study found that persons invited to diabetes screening were no more likely than controls to quit smoking, reduce alcohol consumption, or become more physically active.

Yet the fascination with do-it-yourself medical testing continues. A New York Times article published earlier this week led with the story of Kristi Wood, a 49 year-old woman who was experiencing fatigue and cognitive problems. Rather than seeing a doctor, she turned to a direct-to-consumer testing service which told her that her vitamin D levels were too high, apparently because she had been overdosing on vitamin D supplements. Once she reduced her supplement dose, "she almost immediately felt better." She credited the testing service for making this (obvious) diagnosis and now has a bunch of blood tests repeated every 4 months.

Although Ms. Wood would do well to read Ms. Hobson's FiveThirty Eight article and the U.S. Preventive Services Task Force statement that found insufficient evidence for adults younger than age 65 to take supplemental vitamin D for any reason, at least the results were clear-cut and actionable. That isn't true for most abnormal results, which require clinical context, careful interpretation, and sometimes additional testing, to distinguish a false from a true positive. A normal laboratory range means that the vast majority - but not all - of healthy people's results will be found between these values. Statistically, 1 in every 20 tests is likely to be abnormal simply by chance. Since blood tests are usually ordered in panels, I estimate that about half of my own patients' result reports have at least one item flagged, with nearly all of them being false positives. In the absence of an informed explanation and reassurance from a health professional who spent 4 years in medical school, 3 years in residency, and 12 years in practice, these results could be alarming and/or trigger unnecessary action like starting a potentially harmful testosterone supplement, as did another do-it-yourself testing patient in the New York Times article.

On a related note, a recent blog post by family physician Jennifer Middleton raised some good questions about do-it-yourself screening for ovarian cancer. For $295, a woman concerned about her ovarian cancer risk can request on a commercial website that an instructional kit be shipped directly to her home. According to the website, the test is intended to be "routine." But there's absolutely nothing routine about it. The ongoing randomized trial evaluating the test's effectiveness hasn't yet determined if it causes more good than harm. For women at low risk, the American College of Obstetricians and Gynecologists and the Society of Gynecologic Oncology recommend against being tested. The moral of this story: if you aren't feeling well or worry about getting sick in the future, don't seek out do-it-yourself testing. Don't be duped by companies such as Life Line Screening. Make an appointment to see a family doctor instead.


  1. So, physicians and nurse practitioners are so good and make so few mistakes that they are entitled to determine whether or not a person can purchase a medical test without their permission? Should I need permission from a lumberjack to buy a chain saw? Should I need permission from an English major to purchase a book of poetry? Should I need permission from a cabinet maker to purchase a plane? Sure, I understand that some people will order tests and make decisions I find inconsistent with my approach to medical care. But where is it written that I have the right to impose my approach upon others?

  2. Thank you for your comment. Interesting analogies. Would you order your own colonoscopy? Your own prostate biopsy? Your own diagnostic laparoscopy? Of course not, unless you were a physician with expertise in performing these screening/diagnostic procedures. Blood tests are no different; their performance and interpretation requires medical expertise, just expertise that happens to be intellectual rather than procedural/surgical.

  3. I would add, if you buy a chainsaw, you know you are going to cut a tree down.

    If you order your own PSA (or screen of your choice), you might think twice. If you obtain equivocal results, do you want your own version of the chainsaw? And who pays for the serial testing that follows to determine if you really need that chainsaw (or if that answer is even achievable)?

    Also, think of all your neighbors who might indulge in overgenerous testing. Your rates and taxes all go up to fund them.

    Doctors are not perfect. We get plenty wrong. But my guess is, we would probably perform better than non-providers in pragmatic and rational decision making.

  4. I suspect "some" consumers are very capable of understanding when to seek care and when not to after DIY blood testing. With insurance costs continuing to skyrocket(5000-7000 deductibles to start)and with it taking weeks to get into a primary care Dr... we either need the option to care to for ourselves or the medical world needs a serious overhaul- and honestly, it's America. Instead of bashing DIY testing perhaps 7 years of education could be toward to help creating reference charts or online resources to make DIY care safer. On the other hand, there are many many Americans who are not only educated they simply would struggle cognitively to understand their results, but I suspect they too have to wait weeks to see a Dr. or their costs have skyrocketed to make care prohibitive. I support DIY care.