Blood Test for Alzheimer's?

This week's ALZForum carried a very interesting article on some breakthroughs in diagnosing AD with blood tests.  The article is "With Sudden Progress, Blood Aβ Rivals PET at Detecting Amyloid."

Historically, the proof of AD was in the autopsy, but there have been a number of ways of ruling out other causes in dementia patients and to find strong evidence suggesting AD.  The two best tests for AD have been measuring amyloids in cerebro-spinal fluid from a spinal tap and with an amyloid PET scan.  Both tests are expensive and invasive.  Who wants a spinal tap?  Who wants their blood stream filled with radioactive stuff?  Who wants to pay for a diagnosis that won't alter the treatment path?  Not your insurance company.  On the other hand, what if an inexpensive blood test could detect amyloids with the same confidence as the other tests?  At least one blood test is on the horizon.  Colin Masters of the University of Melbourne, Australia was quoted as saying that blood tests “will become widely available and revolutionize the field in the next few years.”

The article discusses several approaches to measuring blood amyloid, but the most promising is a device called an "antibody-based single-molecule array (Simoa)." The device had been able to detect elevated amyloid in patients with Alzheimer's dementia. The problem has been that the concentrations of amyloids (or proxy substances) in the blood of someone with mild cognitive impairment are infinitesimal and are extremely difficult to measure. How much more so for someone who is presymptomatic. However, the breakthrough this year is a device sufficiently sensitive to detect elevated amyloids in people with mild cognitive impairment (MCI) or even at the presymptomatic stage of AD.

This will revolutionize diagnosis of AD, but what will it mean for the cost of long-term care insurance? My guess is that someone who is found presymptomatic with AD will be completely unable to get insurance.