p-tau217
p-tau217 is the tau protein phosphorylated at threonine 217. It is the most Alzheimer-specific plasma biomarker available right now. Its levels rise early along the amyloid cascade, before any of your cognitive symptoms appear. And they track tightly with amyloid-PET and tau-PET burden. In head-to-head comparisons, plasma p-tau217 beats p-tau181, p-tau231, and several MRI-based markers. It is better at telling Alzheimer's apart from other neurodegenerative diseases. Two-step workflows that use plasma p-tau217 can cut the need for amyloid-PET or spinal-fluid testing. That helps when triaging people with cognitive impairment for anti-amyloid therapy. That said, the handling, the assay platform, and the reference ranges still vary across vendors. The first FDA-cleared blood test for Alzheimer's came in May 2025 (Fujirebio's Lumipulse G pTau217/β-Amyloid 1-42 plasma ratio). It uses a plasma p-tau217 ratio. And Roche got an EU CE mark for its Elecsys pTau217 plasma assay on 12 May 2026.
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Sources
- Palmqvist S, Janelidze S, Quiroz YT, Zetterberg H, Lopera F, Stomrud E, et al.. (2020). Discriminative Accuracy of Plasma Phospho-tau217 for Alzheimer Disease vs Other Neurodegenerative Disorders. *JAMA*doi:10.1001/jama.2020.12134
- Janelidze S, Mattsson N, Palmqvist S, Smith R, Beach TG, Serrano GE, et al.. (2020). Plasma P-tau181 in Alzheimer's disease: relationship to other biomarkers, differential diagnosis, neuropathology and longitudinal progression to Alzheimer's dementia. *Nature Medicine*doi:10.1038/s41591-020-0755-1
- Mattsson-Carlgren N, Janelidze S, Palmqvist S, Cullen N, Svenningsson AL, Strandberg O, et al.. (2020). Longitudinal plasma p-tau217 is increased in early stages of Alzheimer's disease. *Brain*doi:10.1093/brain/awaa286