Plasma p-tau217 yields discordant Alzheimer results in 8.5% of adults
False-negative blood results occurred in 5.6% of participants compared with false positives in 2.8%, with mismatches tied to kidney function, BMI, and clinical stage.
Neurology
Among 706 human participants enrolled in memory and aging studies at Mayo Clinic (median age 70.0 years; 54% male), researchers evaluated the accuracy of plasma phosphorylated tau 217 against amyloid-PET and cerebrospinal fluid biomarkers. Overall, 60 participants (8.5%) had discordant blood test results. False-negative readings (5.6%) were more frequent than false-positive results (2.8%). Mismatches were associated with older age and obstructive sleep apnea. In age-adjusted models, false-negative results were independently linked to earlier clinical stage, higher body mass index, and higher estimated glomerular filtration rate. In contrast, false-positive results were independently tied to advanced clinical dementia and lower estimated glomerular filtration rate. The authors note that clinical disease stage along with factors affecting renal clearance, brain amyloid clearance, and volume of distribution influence plasma test accuracy.
Why it matters
As blood-based biomarkers become standard diagnostic tools for Alzheimer disease, identifying how age-related physiological shifts—such as reduced renal clearance—skew plasma levels is vital. These insights help clinicians identify which patients require confirmatory PET or cerebrospinal fluid testing before starting disease-modifying therapies.
Caveats
The investigation was a retrospective study conducted within Mayo Clinic cohorts. In addition, the analysis only included participants with clearly positive or negative plasma p-tau217 cutoffs, omitting intermediate values.
The paper
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Joshua A. Bornhorst, Daniel J. Figdore, Anas Elgenidi, Christian Lachner, Neill R. Graff‐Radford,Jacksonville College
Neurology · 1 Oct 2026