Alzheimer's Blood Test in Primary Care Could Slash Diagnostic ...

As disease-modifying treatments for Alzheimer's disease (AD) become available, equipping primary care physicians with a highly accurate blood test could significantly reduce diagnostic wait times. Currently, the patient diagnostic journey is often prolonged owing to the limited number of AD specialists, causing concern among healthcare providers and patients alike. Now, a new study suggests that use of high-performing blood tests in primary care could identify potential patients with AD much earlier, possibly reducing wait times for specialist care and receipt of treatment.

"We need to triage in primary care and send preferentially the ones that actually could be eligible for treatment, and not those who are just worried because their grandmother reported that she has Alzheimer's," lead researcher Soeren Mattke, MD, DSc, told Medscape Medical News. 

"By combining a brief cognitive test with an accurate blood test of Alzheimer's pathology in primary care, we can reduce unnecessary referrals, and shorten appointment wait times," said Mattke, director of the Brain Health Observatory at the University of Southern California in Los Angeles.

The findings were presented on July 28 at the Alzheimer's Association International Conference (AAIC) 2024.

Projected Wait Times 100 Months by 2033

The investigators used a Markov model to estimate wait times for patients eligible for AD treatment, taking into account constrained capacity for specialist visits. 

The model included the projected US population of people aged 55 years or older from 2023 to 2032. It assumed that individuals would undergo a brief cognitive assessment in primary care and, if suggestive of early-stage cognitive impairment, be referred to a AD specialist under three scenarios: no blood test, blood test to rule out AD pathology, and blood test to confirm AD pathology.

According to the model, without an accurate blood test for AD pathology, projected wait times to see a specialist are about 12 months in 2024 and will increase to more than 100 months in 2033, largely owing to a lack of specialist appointments. 

In contrast, with the availability of an accurate blood test to rule out AD, average wait times would be just 3 months in 2024 and increase to only about 13 months in 2033, because far fewer patients would need to see a specialist. 

Availability of a blood test to rule in AD pathology in primary care would have a limited effect on wait times because 50% of patients would still undergo confirmatory testing based on expert assumptions, the model suggests. 

Prioritizing Resources 

"Millions of people have mild memory complaints, and if they all start coming to neurologists, it could completely flood the system and create long wait times for everybody," Mattke told Medscape Medical News. 

The problem, he said, is that brief cognitive tests performed in primary care are not particularly specific for mild cognitive impairment. 

"They work pretty well for manifest advanced dementia but for mild cognitive impairment, which is a very subtle, symptomatic disease, they are only about 75% accurate. One quarter are false-positives. That's a lot of people," Mattke said. 

He also noted that although earlier blood tests were about 75% accurate, they are now about 90% accurate, "so we are getting to a level where we can pretty much say with confidence that this is likely Alzheimer's," Mattke said. 

Commenting on this research for Medscape Medical News, Heather Snyder, PhD, vice president of medical and scientific relations at the Alzheimer's Association, said it is clear that blood tests, "once confirmed, could have a significant impact on the wait times" for dementia assessment. 

"After an initial blood test, we might be able to rule out or rule in individuals who should go to a specialist for further follow-up and testing. This allows us to really ensure that we're prioritizing resources accordingly," said Snyder, who was not involved in the study. 

This project was supported by a research contract from C2N Diagnostics, LLC to USC. Mattke serves on the board of directors of Senscio Systems, Inc., and the scientific advisory board of ALZPath and Boston Millennia Partners and has received consulting fees from Biogen, C2N, Eisai, Eli Lilly, Novartis and Roche/Genentech. Snyder has no relevant disclosures.