How Well Do Alzheimer’s Blood Tests Work in the Real World?

Blood tests promise to speed up the diagnostic process for people who doctors suspect may have Alzheimer’s, occasionally replace an expensive or invasive lumbar puncture or brain scan, and in the future they might spot who’s at risk before they develop symptoms . 

But the tests lack real-world validation. One study found that the results of an FDA-cleared blood test may be less accurate than advertised, and the evidence showing that these tests are really improving care is limited, fuelling skepticism among some experts. 

At the Alzheimer’s Association International Conference (AAIC) in London on Tuesday and Wednesday, researchers shared data that’s beginning to answer these questions. 

Integrating blood tests into clinical practice

Dr. Sebastian Palmqvist, a neurologist and an associate professor at Lund University, presented two studies assessing how blood tests affected diagnosis among primary care doctors and dementia specialists. 

The research included over 1,300 participants suspected of having Alzheimer’s. After taking a patient history and neurocognitive testing, the doctors or dementia specialists were asked to make a diagnosis. Then, they received results from a PrecivityAD2 blood test, which measures multiple biomarkers of Alzheimer’s, to see if that changed their care. 

To verify the diagnosis, each participant also received a gold-standard cerebrospinal fluid or amyloid PET scan for validation.

After receiving the results, primary care doctors were 88 percent accurate in their diagnosis while specialists were 93 percent accurate. The test was especially useful for ruling out Alzheimer’s in primary care because of its ability to correctly pick out people who don’t have biomarkers, meaning they send less people to a specialist for a workup after. 

The blood test led doctors and specialists to change the diagnosis more than 25 percent of the time, and changed care more than 60 percent of the time since it made them more confident with the diagnosis. Another study of dementia specialists found similar benefits.

“You get a blood test that actually confirms your suspicion,” Palmqvist told Being Patient. “Now you are ready to act.” While anti-amyloid treatments that are approved in Europe aren’t readily available across the European Union since they aren’t covered by insurers, he added that this testing is still effective since it allows doctors to prescribe drugs that may treat the cognitive symptoms, like cholinesterase inhibitors.

Dr. Henrik Zetterberg, a professor at the University of Gothenburg, and a visiting professor at UW−Madison and at University College London, who wasn’t involved in the research, told Being Patient that the blood tests could help primary care physicians effectively rule out Alzheimer’s as a potential diagnosis. “It will reduce the burden on specialty care,” said Zetterberg. 

Still, other experts are skeptical that these tests are ready for primary care. “These tests should really be only ordered by the memory specialist and interpreted by the memory specialist in this setting,” neurologist Jonathan Moray of Tufts Medicine New England Neurological Associates told Being Patient. 

He said he has seen these tests being used incorrectly by doctors, potentially leading to false positives. 

Can pTau-217 in healthy people predict Alzheimer’s risk?

Rachel Buckley, an associate professor at Harvard Medical School wanted to know whether blood tests might predict which healthy individuals would develop the disease. 

Her team combed through data collected from over 2,700 cognitively healthy older Americans that participated in one of five different studies tracking brain health as they aged. The study presented at AAIC, and simultaneously published in JAMA, found that higher levels of the blood biomarker pTau-217 — which they correlated to very high levels of beta-amyloid plaque observed through gold standard amyloid PET scans — upped the risk of cognitive decline. 

At the highest measure of pTau-217, participants had a 38 percent chance of progressing to cognitive impairment within five years and 78 percent chance over 10 years. Elevated levels carried a significant 15 percent risk over five years and 45 percent risk over 10 years. The researchers did not see any differences between men and women. 

Zetterberg said he was “very encouraged by the results.” Using a digital cognitive assessment — a phone or tablet test that looks for the smallest changes in cognitive ability —  that could look for the very earliest signs of thinking and memory problems, he believes, could be the first step in a future screening assessment. If someone has these subtle signs, then the pTau-217 test might be even more predictive about their future risk. 

Still, Buckley cautioned that her study is just the first step to understanding what blood tests mean for healthy individuals and will be revised as more research develops. For someone without cognitive impairment, the advice remains the same whether or not they test positive on a blood test. 

“Whatever is good for your heart is good for your brain,” said Buckley. “Keep up your physical activity, keep up your cognitive activity, try to eat well, try to sleep as best you can.”