Will there soon be a blood test?
My father-in-law recently passed away after suffering with Alzheimer’s for several years. I also have an aunt who is currently living with some form of dementia, probably vascular.
Few diseases strike more fear into those over the age of 50 than Alzheimer’s. Needless to say, both my husband and I worry when we find ourselves saying:
“Oh, what’s the word I want?”
or “Where did I put it?”
or “Why did I come in here?”
So when I read the prevailing health headlines this week about a blood test to predict Alzheimer’s, I was both a little intrigued and a little frightened. Is such a test really on the horizon? And what would it mean to me and other Baby Boomers?
The original report that all the news sources were quoting was published in Nature Medicine earlier this month. In short, the study proposes a blood test that measures certain lipids, or pieces of cell membranes; a specific pattern of these lipids could, they attest, predict “…either amnesic mild cognitive impairment or Alzheimer’s disease within a 2–3 year time frame with over 90% accuracy.”
Such a test would be important, the researchers argue, because currently “there are no cures or disease-modifying therapies,” but maybe more could be done if we could “detect the disease before it has progressed to produce evident memory loss and functional decline.”
Accuracy and benefits oversold?
After reading the articles, I popped over to my favorite health news blog, Health News Review. Gary Schwitzer is a wizard at analyzing the statistical truthfulness of these popular health stories.
According to Gary:
Dozens and dozens of stories reported the study with no independent scientific perspective and with little or no discussion of the ethics questions involved in an Alzheimer’s test – when there is currently no effective treatment for the disease.
A far more fundamental question of evidence was raised right in the headline of MedPageToday’s story, “Blood Test for Alzheimer’s Disease — Oversold?“ Immediately in the first paragraph, John Gever wrote that “the accuracy fell short of what would normally be acceptable for a screening test.” He went on to explain:
If the study cohort’s 5% rate of conversion from normal cognition to mild impairment or Alzheimer’s disease is representative of a real-world screening population, then the test would have a positive predictive value of just 35%. That is, nearly two-thirds of positive screening results would be false. [my emphasis]
Two-thirds of tests would be false positives? That’s hardly a 90% accuracy rate, is it?
There’s no doubt that whoever develops a screening test for Alzheimer’s, either a blood test or a CT scan, will make a lot of money from it, so the quest for such a test will continue.
But it begs the question: Will screening for Alzheimer’s really be beneficial? Will anyone want it?
Bottom line: Would you want to know?
Me, personally, no. My husband also said no, he wouldn’t want to know.
There is already a genetic test available to see if you have a gene that would make you more likely to develop Alzheimer’s, although it is not completely predictive.
Some want this information, so they can make necessary financial plans. But as more and more people are living well into their 80s, and dementia is more common as we age, we should all be making financial plans that take some form of long-term care into account.
And as an NPR article on this blood test story points out:
. . . people who have the Alzheimer’s gene and know it tend to rate their own memories as worse than people who have the gene but don’t know it, he says. Knowing you carry the gene also seems to hurt people’s performance on memory tests.
Sometimes ignorance is bliss.
It does not seem sensible to me to develop a widely-used screening test for a disease, no matter how accurate it is, before there is some advantageous treatment to offer. Until then, I’d rather not know.
How about you? Would you want to know?