PrecivityAD2 can help clinicians assess amyloid pathology associated with Alzheimer’s disease in people who already have cognitive symptoms. Its US-cleared indication is for use alongside a clinical assessment, rather than screening symptom-free people or making a diagnosis from a blood result alone.
That distinction is more useful than treating an accuracy percentage as a complete answer. The test’s biological target, the population in which it was evaluated and the version actually being offered all affect what a result can mean.
A blood sample and a clinical diagnosis answer different questions
The FDA’s public decision and submission describe a test for adults aged 40 and over presenting with signs or symptoms of cognitive impairment. It combines measurements of amyloid and tau-related markers into an Amyloid Probability Score 2, or APS2.
The target is evidence of brain amyloid pathology. A clinician’s assessment has a wider task: understanding a person’s symptoms, other possible explanations and the information needed to reach a diagnosis. The indication explicitly excludes standalone diagnosis and general screening.
This is also why the result should not be read as a timetable. A pathology-related score does not, by itself, forecast how quickly a particular person’s memory or daily functioning will change.
The Alzheimer’s Association’s explanation of the clearance places blood biomarkers within that larger diagnostic process, alongside medical history, cognitive and functional assessment and other investigations as appropriate. That is the organisation’s diagnostic-context explanation, not proof that one test can replace every other part of an evaluation.
Why the categories matter beside an accuracy claim
The FDA submission reports Positive, Likely Positive and Negative categories. Their names should not be collapsed into a binary promise that every blood draw either confirms or excludes clinical Alzheimer’s disease.
In the pooled validation population of 1,142 people, the reported predictive values depended on the prevalence of amyloid pathology in that population. A positive predictive value describes the proportion of people with a specified positive result who had the reference finding. It is not the same quantity as sensitivity, and it is not a universal probability for every person tested in every setting.
| Question | What needs to be distinguished |
|---|---|
| What is being detected? | Amyloid pathology associated with the disease, rather than every cause of cognitive symptoms. |
| Who was the test intended for? | Symptomatic adults undergoing evaluation, rather than a symptom-free screening population. |
| What does a category mean? | Evidence to interpret with the clinical assessment, rather than a diagnosis from the category name alone. |
| Which performance measure is quoted? | Predictive value, sensitivity and specificity answer different statistical questions. |
These distinctions explain why a simplified “over 90% accurate” description cannot carry the full meaning of the validation.
The test’s origins and commercial version
Washington University’s account describes the development of underlying technology and its commercialisation by C2N Diagnostics. The approach uses mass spectrometry to measure the biomarkers. The university also identifies the startup and licensing relationships; its account is connected to the technology’s development, rather than an independent comparison of all available tests.
There is a further practical distinction in C2N’s current product information. At this check, the company says its currently available PrecivityAD2 offering is a laboratory-developed test under CLIA regulations, while the FDA-cleared version is expected in the coming months.
The shared name therefore does not justify assuming that any available order is automatically the cleared version. Nor does US clearance establish availability, reimbursement or an equivalent regulatory position in another country. Those are separate questions about a particular service and jurisdiction.
What the result cannot settle on its own
Our explainer on the FDA’s Alzheimer’s prevention accelerator concerns a research initiative, a different stage from symptomatic diagnostic evaluation. A diagnostic biomarker, an intervention study and a treatment decision should remain distinct even when they concern the same disease.
For PrecivityAD2, the useful promise is a bounded one: another source of evidence for clinicians evaluating cognitive symptoms. Understanding that role, the reported category and the offered test version is more informative than interpreting a commercial accuracy headline as a complete diagnosis.