Blood test spots patients eligible for therapies targeting amyloid-beta

ALZpath test makes use of tau biomarker to identify amyloid plaques

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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A dropper squirting blood is shown alongside four half-filled test tubes.

A commercially available blood test, sold by ALZpath, can identify with high accuracy Alzheimer’s disease patients who are likely to be eligible for new treatments, a study suggests.

By detecting a version of the tau protein in a blood sample, the “ALZpath pTau217 test can help healthcare providers determine the presence of amyloid plaques in the brain — a hallmark of Alzheimer’s disease,” Andreas Jeromin, PhD, chief scientific officer at ALZpath and a study author, said in a company press release.

“This diagnostic capability offers increasingly vital aid in medical management and treatment decisions for Alzheimer’s, especially as new disease-modifying treatments become more accessible,” Jeromin added.

The study, “Diagnostic Accuracy of a Plasma Phosphorylated Tau 217 Immunoassay for Alzheimer Disease Pathology,” was published in JAMA Neurology. ALZpath provided the materials for the study.

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Phosphorylated tau 217 is protein version seen in disease’s hallmark clumps

Alzheimer’s disease is marked by clumps in the brain of two proteins, amyloid-beta and tau. Identifying these toxic clumps is increasingly important for an accurate disease diagnosis, especially as new therapies emerge.

Currently, the only way to reliably detect these protein clumps is via advanced imaging or by taking a sample of the cerebrospinal fluid (CSF) that surrounds the brain and spine — procedures that are expensive and can be burdensome for patients. A blood test that could accurately identify patients with these clumps would make the diagnostic procedure easier and improve timely access to treatment.

ALZpath’s test checks the blood for phosphorylated tau 217 (pTau217), which is a version of the tau protein possessing a specific chemical modification that’s typically seen in Alzheimer’s-related clumps.

In this study, a team of scientists compared outcomes from ALZpath’s pTau217 test against established methods to detect amyloid-beta or tau. Data were compared in three separate groups totaling more than 700 patients, which included people without cognitive impairment, with mild cognitive impairment, and with dementia caused by or not associated with Alzheimer’s disease.

To determine the test’s accuracy, the scientists calculated a statistical measure called the AUC (area under the receiver operating characteristic curve). This is a measure of how well a given test — in this case, the pTau217 blood test — is able to distinguish between two groups. Here, those groups were individuals with or without brain protein clumps as measured by imaging or CSF samples.

AUC values can range from 0.5 to 1. Higher numbers indicate that the test is better at accurately distinguishing between the two groups.

Good accuracy in detecting amyloid-beta and tau clumps via patients’ blood

Across all three groups in the study, the pTau217 test showed good accuracy for detecting both types of protein clumps. Specifically, for amyloid-beta, AUC values ranged from 0.92 to 0.96, and for tau, values ranged from 0.93 to 0.97.

“This is an instrumental finding in blood-based biomarkers for Alzheimer’s, paving the way for the clinical use of the ALZpath pTau 217 assay,” said Kaj Blennow, MD, PhD, and Henrik Zetterberg, MD, PhD, study co-authors at the University of Gothenburg in Sweden.

Since the test was highly accurate for detecting amyloid-beta, the scientists proposed that it could be used as a first step in checking if patients might be eligible for new therapies targeting these protein clumps.

Specifically, they proposed a three-tiered system: individuals with very high pTau217 results on the blood test can be assumed to be positive for amyloid-beta, while those with very low results can be assumed to be negative. Patients with intermediate results can be referred for further testing with imaging or CSF analysis.

The researchers estimated that use of this tiered system would mean only about 20% of patients would need to go through confirmatory tests.

“These results emphasize the important role of plasma p-tau217 as an initial screening tool in the management of cognitive impairment by underlining those who may benefit from antiamyloid immunotherapies,” the scientists concluded.