Blood-based biomarkers now detect Alzheimer's pathology well enough that the question has shifted from whether they work to where they should be used. This Personal View argues that moving them into primary care fails on infrastructure rather than on assay performance.
The argument runs through pretest probability. Specialist memory services see a selected population with a high prior probability of Alzheimer's pathology, and a biomarker result there sits inside an established diagnostic sequence. Primary care populations are low-prevalence and clinically heterogeneous, so the same result carries a different meaning patient by patient — and without firm clinical anchoring, the authors warn, testing drifts from diagnosis towards case-finding and then towards something close to screening, which nobody has agreed to.
Their sharpest point concerns the rule-out use that is usually offered as the safe application. A negative result is only worth having if it changes what happens next. Where the alternative pathway is the same investigation, the same referral and the same follow-up, the test has consumed resource and anxiety and altered nothing. Their conclusion is not prohibition but discipline: selective, clinically anchored, pathway-dependent use until guidance and services catch up.
- Ask what a negative result would change before ordering one
- Anchor any request to a defined clinical syndrome, not to a worried patient's request
- Recognise that pretest probability in general practice is not the trial population's
- Do not let a biomarker substitute for the cognitive and functional assessment
- Agree locally what pathway a positive result enters before offering the test at all
Why it matters
It moves the debate from test accuracy, which is settled, to what a result is for — which is not.
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