Inroduction: Plasma phosphorylated tau217 (p-tau217) is a biomarker for the detection of amyloid pathology. We present performance characteristics of the Lilly SP-X P-tau217 assay in a clinical validation cohort, as a whole and divided into subpopulations from traditionally underrepresented groups.
Methods: We measured p-tau217 levels in plasma samples from participants with mild cognitive impairment. Assay performance in predicting positivity for amyloid beta (Aβ) positron emission tomography was examined using two numerical cutoffs.
Results: Two p-tau217 cutoffs were determined with an upper-level group with 95% positive predictive value for Aβ positivity and a lower-level group with 84% negative predictive value for Aβ negativity, with 91% sensitivity and 90% specificity. The remaining indeterminate group represented 18% of participant samples. Similar performance was observed across validation subgroups.
Discussion: The validation data support the potential clinical utility of the SP-X p-tau217 assay in multiple subpopulations to aid in Alzheimer's disease diagnosis.
Highlights: The Lilly SP-X p-tau217 assay showed strong concordance with amyloid PET in total cohort and underrepresented groups.Assay performance is in line with guidance from the Global CEOi on AD Working Group.Data support the clinical utility of the assay in multiple cohorts to aid in AD diagnosis.
Keywords: Alzheimer's disease; blood‐based biomarkers; immunoassay; laboratory‐developed test; p‐tau217; underrepresented populations.
© 2025 The Author(s). Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring published by Wiley Periodicals, LLC on behalf of Alzheimer's Association.