JAMA Neurol

Alzheimer's blood test could be used to screen even before symptom onset

January 23, 2024

A commercially available plasma p-tau217 immunoassay accurately identified biological Alzheimer disease (AD), comparable with results using cerebrospinal fluid (CSF) biomarkers, with reproducible cut-offs across three cohorts. Testing for elevated levels of the beta amyloid was up to 96 percent accurate and testing for tau was up to 97 percent accurate.

• Phosphorylated tau (p-tau) is a specific blood biomarker for AD pathology, with p-tau217 considered to have the most utility.
• This cohort study included 786 participants (mean age, 66.3 years; 504 females [64.1%] and 282 males [35.9%]).
• Researchers examined data from 3 single-center observational cohorts: cross-sectional and longitudinal data from the Translational Biomarkers in Aging and Dementia (TRIAD) cohort (visits October 2017–August 2021) and Wisconsin Registry for Alzheimer’s Prevention (WRAP) cohort (visits February 2007–November 2020) and cross-sectional data from the Sant Pau Initiative on Neurodegeneration (SPIN) cohort (baseline visits March 2009–November 2021).
• Participants included individuals with and without cognitive impairment grouped by amyloid and tau (AT) status using PET or CSF biomarkers.
• Data were analyzed from February to June 2023.
• High accuracy was observed in identifying elevated Aβ (area under the curve [AUC], 0.92-0.96; 95% CI, 0.89-0.99) and tau pathology (AUC, 0.93-0.97; 95% CI, 0.84-0.99) across all cohorts. These accuracies were comparable with CSF biomarkers in determining abnormal PET signal.
• The detection of abnormal Aβ pathology using a 3-range reference yielded reproducible results and reduced confirmatory testing by approximately 80%.
• Longitudinally, plasma p-tau217 values showed an annual increase only in Aβ-positive individuals, with the highest increase observed in those with tau positivity.
• Study authors note that this high-performing assay also detected longitudinal changes, including at the preclinical stage, potentially resulting in less expensive and more rapid screening.

Source:

Ashton N, et al. (2024, January 22.) JAMA Neurol. Diagnostic Accuracy of a Plasma Phosphorylated Tau 217 Immunoassay for Alzheimer Disease Pathology. https://pubmed.ncbi.nlm.nih.gov/38252443/