Finger prick blood sample can detect Alzheimer's biomarkers

Reviewed by Danielle Ellis, B.Sc.Jul 19 2023

Advancements in technology and practice reported for the first time at AAIC 2023 demonstrate the simplicity, transportability and diagnostic value of blood-based biomarkers for Alzheimer's, including the future potential for at-home testing by a patient or a family member.

These findings are timely and important with the recent U.S. Food and Drug Administration approvals of Alzheimer's treatments targeting amyloid-beta where confirmation of amyloid buildup and biomarker monitoring are required to receive treatment. Blood tests — once verified and approved — would offer a quick, noninvasive and cost-effective option."

Maria C. Carrillo, Ph.D., Alzheimer's Association chief science officer

Blood tests are already being implemented in Alzheimer's drug trials for further verification of their effectiveness and for screening potential participants, which would be a significant evolution from more expensive and invasive procedures that are currently common practice. In some cases, these blood tests are providing similar information to "gold standard" testing, such as brain imaging scans and cerebrospinal fluid analysis.

"While further standardization and validation are needed, blood tests may soon be an important piece of the diagnostic workup in everyday practice for detecting and monitoring treatment of Alzheimer's disease," Carrillo said.

Finger prick blood sample detects Alzheimer's biomarkers; travels easily between countries

Hanna Huber, Ph.D., of the Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, University of Gothenburg, Sweden, and colleagues set out to simplify and increase the accessibility of blood tests by developing a finger prick blood collection to measure key Alzheimer's-related biomarkers neurofilament light (NfL), glial fibrillary acidic protein (GFAP) and phosphorylated tau (p-tau181 and 217).

They collected blood (from both vein and finger prick) from 77 memory clinic patients from the ACE Alzheimer Center, Barcelona. The blood samples were transferred onto dry blood spot cards and shipped overnight, without temperature control or cooling, to the University of Gothenburg, Sweden. There, the dried blood samples were extracted from the cards, and NfL, GFAP and p-tau181 and 217 were measured. (Note: p-tau217 data is only available in 11 people.) All were detectable in the finger prick samples.

In the vein blood spots, the levels of GFAP, NfL, p-tau217 and p-tau181 associated strongly with standard blood analysis. GFAP, NfL and p-tau217 extracted from finger prick blood also correlated highly with standard blood collection.

"Our pilot study demonstrates the potential of remote collection and measurement of Alzheimer's biomarkers without low-temperature storage or extraordinary preparation or processing," Huber said. "Currently, use of Alzheimer's blood tests is limited by the need to visit a clinic, administration by trained personnel, and strict time-limited and temperature-dependent delivery and storage procedures. A method that allows blood collection at home and that is simple enough to be performed independently, or by caregivers, would increase accessibility of these tests. It would result in improved early diagnosis and better monitoring of patients considered 'at risk' or those who are receiving approved therapies."

Blood tests may improve Alzheimer's diagnosis in primary care

Sebastian Palmqvist, M.D., Ph.D., of the Clinical Memory Research Unit at Lund University, Sweden, and colleagues with the BioFINDER-Primary Care study conducted the first study to examine the use of blood-based biomarkers for Alzheimer's in primary care and compare them to the diagnostic accuracy of primary care physicians (PCPs).

The study recruited 307 middle-aged to elderly patients at 17 primary care centers in Sweden (mean age=76, 48% women). After an office visit, cognitive testing and a CT scan or MRI of the brain, the PCPs registered their diagnosis, the likely biological cause(s) and proposed a treatment plan for each study participant.

At the same time, a blood sample was collected and analyzed to determine the concentrations of beta-amyloid and phosphorylated tau using the PrecivityAD2 test by C2N Diagnostics (USA). Levels of these two markers were combined into a score called the Amyloid Probability Score 2 (APS2). All patients then underwent a thorough clinical examination at a specialized memory clinic, including evaluation by a specialist blinded to the blood sample result.

The PCPs correctly identified the presence of Alzheimer's-related changes or correctly diagnosed Alzheimer's in approximately 55% of the cases, while the blood test did so in more than 85% of the cases. Other findings:

• The PCPs indicated their certainty about the diagnosis was less than 50%.
• The treatment plans revealed that, due to incorrect diagnosis, more than 50% of people who actually had Alzheimer's did not receive symptomatic treatment, and 30% of non-Alzheimer's cases incorrectly received symptomatic treatment.

"Due to the lack of accurate diagnostic tools, it is currently very difficult for primary care doctors to identify Alzheimer's disease, even among patients with cognitive impairment," Palmqvist said. "This too often leads to diagnostic uncertainty and inappropriate treatment. Blood tests for Alzheimer's disease have great potential for improving diagnostic accuracy and proper treatment of people with Alzheimer's. These tests may become even more important in the near future, as new drugs that slow down the disease in its early stages become more widely available."