A Lancet Neurology review sets out where fluid biomarkers now sit in dementia care. Blood-based phosphorylated tau 217 for Alzheimer's disease, and neurofilament light for frontotemporal dementia and amyotrophic lateral sclerosis, have moved from research into clinical implementation, aided by ultrasensitive assays.

The timing matters because amyloid-targeting treatments are becoming available and need a confirmed molecular diagnosis. But the review is clear that one marker is not enough: capturing the vascular, alpha-synuclein and TDP-43 pathologies that also drive dementia, and the heterogeneity in treatment course, will need panels rather than a single test.

For practice, a blood p-tau217 is becoming a realistic first step in working up suspected Alzheimer's, potentially reducing reliance on amyloid PET or lumbar puncture, but it supports rather than replaces a careful clinical assessment, and local pathways and appropriate-use criteria still apply.

Blood p-tau217 for Alzheimer's and neurofilament light for FTD and ALS are now reaching clinical use.
Their arrival is timely as amyloid-targeting therapies require molecular confirmation.
No single marker captures the vascular, alpha-synuclein and TDP-43 copathologies of dementia.
Use a blood biomarker to support, not replace, clinical assessment.
Follow local pathways and appropriate-use criteria before acting on a result.

Why it matters

It changes the practical route to a molecular Alzheimer's diagnosis just as disease-modifying therapy makes that diagnosis consequential.

Don't overread it

This is a narrative review; blood biomarkers complement established diagnostic pathways and have defined appropriate-use limits rather than replacing clinical judgement.