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Finger-Prick Blood Test Promising for Alzheimer’s Diagnosis, Monitoring

A finger-prick blood test can accurately identify key Alzheimer’s disease (AD) biomarkers without the need for temperature or storage control measures, results of a new pilot study suggest.

“The study showed we can detect a broad range of biomarkers that are related to AD in venous blood after spotting it to a dry blood card but also in capillary blood obtained with a finger prick,” lead investigator Hanna Huber, PhD, Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, University of Gothenburg, Mölndal, Sweden, told Medscape Medical News.

The findings were presented at the Alzheimer’s Association International Conference (AAIC) 2023.

A Single Drop of Blood

The use of blood samples to detect amyloid and other markers of AD ― including neurofilament light (NfL), glial fibrillary acidic protein (GFAP), and phosphorylated tau (p-tau) ― has become standard procedure for monitoring patients in clinical trials. But this presents logistical challenges because it requires access to on-site sampling with strict, time-limited, temperature-dependent protocols.

To increase the utility of these key biomarkers, the researchers conducted a pilot study that investigated a novel way of quantifying them in capillary and venous dry blood spots. The test involves dropping a small blood sample onto a blood spot card, where it dries and remains at room temperature.

To investigate the accuracy of the test, the investigators recruited 77 volunteers who were attending a memory clinic in Barcelona. Capillary whole blood samples were obtained using the normal venous puncture method and also from a finger prick, similar to diabetes blood testing.

In a subset of 28 patients, the investigators also obtained cerebrospinal fluid samples, which represent the “absolute gold standard of AD diagnostics,” study co-investigator Nicholas Ashton, PhD, associate professor, Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, University of Gothenburg, told Medscape Medical News.

The blood samples were shipped overnight without temperature control or cooling to Gothenburg Sweden, where they were extracted from the blood spot cards and tested for the presence of AD biomarkers.

Results showed an “extremely good relationship” between information from blood obtained through the normal method and that from a single finger prick.

“We’re saying we can measure NFL, GFAP, and phosphoralated tau 217, which are now established markers for AD, all in a single finger prick, which means you don’t need to do centrifugation, you don’t need to freeze the sample, it can be done anywhere,” said Ashton.

If the test is validated in larger trials, it could mean that in the future, patients with memory complaints could be assessed remotely by completing a standard memory test online and using a mail-in blood spot card.

Not only could this potentially facilitate earlier diagnosis, but it could also be used to regularly monitor treatment response. Ashton noted that this is especially important now that disease-modifying drugs are becoming available.

“If you’re receiving one of these treatments, you can send tests back to a laboratory to see how you’re progressing on the drug. It isn’t just a blanket 6-month check-up when you’re on a drug; it can be followed on a weekly basis and personalized to the person who is on the medicine.”

The study shows that the samples remain stable for up to a month at room temperature, which is “really encouraging,” although there are still some challenges with unsupervised blood collection, said Ashton.

AD Diagnosis in Primary Care

Another study presented at the conference showed that a blood test for AD pathology greatly improves diagnostic accuracy in primary care.

“We now have data supporting the use of blood-based biomarkers in clinical practice,” study investigator Sabastian Palmqvist, MD, PhD, associate professor, clinical memory research unit, Lund University, Sweden, told Medscape Medical News.

While certain blood tests can very accurately identify AD pathology, “we had no idea how they perform in primary care populations where people tend to seek help for cognitive complaints,” said Palmqvist.

The study included 307 patients (mean age, 76 years) with cognitive complaints at 25 primary care centers in Sweden.

After a standard workup, which typically involved cognitive screening, imagining, clinical assessment, and ruling out secondary causes, primary care physicians (PCPs) were asked what they thought was the most likely cause of cognitive impairment and how certain they were of their diagnosis.

Researchers also obtained plasma biomarkers, including p-tau217 Ratio and Aβ42/Aβ40 Ratio. The outcome was AD pathology.

Investigators found that the accuracy of the doctor diagnoses was about 55%, said Palmqvist. He noted that “this wasn’t’ better than just random chance.”

This compares to 87% accuracy using blood-based biomarkers.

“We found it was very difficult for the PCPs to make an accurate diagnosis of AD”, said Palmqvist. “It’s not that they have poor judgment; it’s just that they don’t have the correct tools.”

Timely, Important Research

Commenting on the research for Medscape Medical News, Percy Griffin, PhD, director of scientific engagement, Alzheimer’s Association, said the fact that the study showed that finger-prick blood samples can be dried and shipped overnight without temperature control might lead to earlier and more accurate diagnoses of AD in areas with relatively few resources. In addition, this type of test could facilitate easier monitoring of high-risk patients receiving therapies, he said.

However, he noted that it is a pilot study, and the results need to be replicated.

The blood tests were more accurate in identifying AD than were primary care physicians, so these results are important; inaccuracy “all too often leads to uncertainty and potentially inappropriate treatment,” said Griffin.

“So again, this is showing the great potential of blood tests to improve diagnostic accuracy and appropriate treatment.”

Given the recent approvals of anti-amyloid drugs, these two studies are “timely and important,” said Griffin. “For all these treatments, there needs to be confirmation of amyloid beta build-up, which is a biomarker that needs to be monitored.”

The finger-prick study was funded by the Alzheimer’s Fund of Sweden. The primary care study was funded by the Alzheimer’s Association. The investigators report no relevant disclosures.

Alzheimer’s Association International Conference (AAIC) 2023: Abstract 80275 (finger-prick blood test); Abstract 78819 (primary care). Both were presented July 19, 2023.

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