Header: See a detailed review of rapidly emerging Alzheimer blood tess, especially pTau217.
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I did an MD-PhD with the intention of working in Alzheimer's research, and neuro disease was my focus from 1988 to 2001. Even in the 90's, there were regularly promises of a new Alzheimer blood test, which never panned out.
So I was excited to see a feature article in 360Dx by Adam Bonislawski about the rapid publications and advances in Alzheimer blood tests. Both plasma ABeta 42/40 ratio and Tau epitopes are promising. The article focuses on large new clinical reports that highligh phopho-Tau 217.
Bonislawsky writes,
- "Plasma phosphorylated-tau 217 (p-tau 217) has emerged as a highly promising marker of the brain amyloid pathology characteristic of Alzheimer's and one that could lessen demand for plasma amyloid-beta 42/40 (Aβ42/Aβ40), the first blood-based marker for the disease to come to market."
New papers include Yu et al., Plasma p-tau181 and p-tau217 in discriminating PART, AD and other key neuropathologies in older adults. And Ashton et al., Diagnostic ccuracy of a Plasma Phosphorylated Tau 217 Immunoassay for Alzheimer Disease pathology.
Twists and Ins and Outs
I think a couple factors have made the space hard to summarize. First, as these titles indicate, it's not just "tau" or even "phospho-tau" but specific epitopes may behave differently.
Then, there is not one single "phospho tau 217" assay. Most assays require two antibodies, a capture and a detection, and those will vary among platforms.
Then, there are different detection platforms (e.g. the Quanterix Simoa technology is a differentiated technology).
Finally, even when those platform variables are settled, there are many ins and outs to defining sensitivity and specificity. Is there a gold standard besides autopsy? What do decimal-point clinical statistics mean, if the clinical gold standard is wrong 20% or 30% of the time?
And what populations does a statistic pertain to? Health controls versus advanced patients? That probably gives the best statistics but it compares extremes that don't match a clinical question (which is in the early symptoms patient.) So if someone pronounces a factoid like, "Plasma tau is 81.5% specific" you really don't know what that means without more facts.
