Novel, Commercially Available Blood Test for Detecting Alzheimer Disease Shows Great Promise

A novel blood test of the biomarker phosphorylated tau (p-tau) could be used to effectively screen for Alzheimer disease (AD), even before the onset of symptoms, according to a study published this week in JAMA Neurology.

Blood biomarkers have emerged as a scalable and viable tool for AD evaluation, trial recruitment, and disease monitoring, investigators noted. The use of blood tests may substantially reduce reliance on cerebrospinal fluid (CSF) or positron emission tomography (PET) scans. Specifically, the amyloid β 42/40 (Aβ42/40) ratio, a validated CSF biomarker, “has limitations in blood and lacks the robustness required for routine clinical testing.”

A robust and accurate blood-based biomarker would enable a more comprehensive assessment of AD and lead to timely access to disease-modifying AD therapies. Plasma phosphorylated tau 217 (p-tau217) is the leading candidate, demonstrating superior diagnostic accuracy and disease specificity compared with other candidates, according to the researchers. It is considered the primary blood biomarker for AD pathology throughout all disease stages.

In their cohort study, researchers analyzed the utility of ALZpath pTau217, a novel and commercially available immunoassay for plasma p-tau217, to detect the presence of AD in the blood. The population of interest included 786 individuals with and without cognitive impairment grouped by amyloid and tau (AT) status using PET or CSF biomarkers. The main outcome of interest was the accuracy of plasma p-tau217 in detecting abnormal levels of AT pathology and longitudinal p-tau217 change according to baseline pathology status.

The ALZpath pTau217 assay demonstrated high accuracy in identifying elevated Aβ (96%) and tau pathology (97%) across all cohorts. The researchers noted that these accuracies were comparable with CSF biomarkers in determining abnormal PET signal. Overall, the test was shown to be definitive in 80% of study subjects.

“This study highlights the effectiveness of a commercially available plasma p-tau217 assay in identifying AD pathology. Our findings demonstrate the substantial reduction of confirmatory testing (by approximately 80%) by implementing a 3-range approach for Aβ positivity based on plasma p-tau217,” the researchers wrote. “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.”