Plasma biomarker testing is displacing amyloid PET as the screening modality for anti-amyloid eligibility

Signal

The standard 2023 pathway from cognitive complaint to anti-amyloid treatment ran through amyloid PET as the confirmatory test for amyloid pathology. The pathway in 2026 is starting to look different. C2N's PrecivityAD2 plasma assay (FDA-cleared 2024), Roche's Elecsys plasma p-tau 217 (rolling out across major reference labs through 2024-2025), and Lilly's TauviD plasma assay together cover the screening step at a fraction of the cost and infrastructure burden of amyloid PET.

Real-world adoption is uneven but trajectory-positive. Tertiary centres with established Alzheimer's clinics are using plasma p-tau 217 as the front-line screen, reserving amyloid PET for cases where the plasma test is equivocal or where the patient's insurance still requires PET as the qualifying biomarker. Community neurology - where the next wave of growth is - has been slower, gated on payer coverage of the plasma tests and on workflow integration.

Why it matters

For commercial teams, plasma displacing PET shifts the addressable population. PET capacity in the US (3,000 scanners, concentrated in academic centres) is a hard ceiling on how many patients can be screened. Plasma testing is run in any reference lab, removes the geographic and capital barrier, and shortens the workup from weeks (PET scheduling) to days (blood draw and central-lab turnaround).

For payers, the substitution lowers the screening cost per qualifying patient by an order of magnitude. The trade-off is that plasma p-tau 217 has lower specificity than amyloid PET, so a positive plasma result followed by anti-amyloid initiation without confirmatory PET implies accepting a small false-positive rate in a setting where false-positive treatment carries real ARIA risk. Most coverage policies still require confirmatory PET or CSF; the question is when that requirement softens.

What we are watching

• Coverage policy evolution at CMS and the major commercial payers (UnitedHealthcare, Anthem, Aetna) on whether plasma alone is qualifying or requires confirmatory imaging.
• Plasma assay reimbursement codes and rates - if the codes do not adequately compensate, even covered tests get deprioritised in lab workflows.
• The next generation of plasma tests with higher specificity, narrowing the gap to PET.
• Community-neurology adoption patterns. Most centres still default to PET when in doubt; the shift to plasma-first is happening but uneven across markets.