There's likely a test. Would you really want to know the result?
When my oldest son was a newborn he had an obvious birth defect that at first seemed cosmetic, but, as we soon understood, might well involve severe brain involvement, leading to intractable epilepsy, with risks of severe intellectual impairment.
The first doctor to treat the cosmetic effects was something of an asshole, first claiming my son would not need anesthesia for treatment - a blatant lie designed to keep him from going to another department in his institution - but worse, when I asked him if my son should have a brain scan to understand if he would face the complications, said, coldly, "I don't know why you'd want to have a test. There's no treatment." (Actually, for epilepsy, there was a known treatment - brain surgery - but happily my son didn't require it)
Happily my son's brain involvement didn't materialize. He's 30 years old now, doing fine and we're very proud of him.
Still, I'll never forget that moment. We changed doctors of course.
Now I'm an old man, and occasionally things do slip my mind, and so I was reminded of that doctor for my own case:
From my Tech News Feed: New Low-Cost Blood Test Detects Five Biomarkers of Alzheimer's Disease
Excerpt:
Scientists have found several reliable blood-based biomarkers of Alzheimer’s disease. These proteins, including amyloid and tau, build up in the brain—and blood—as the disease progresses. A blood test for these proteins can help catch the disease in its earliest stages, when treatment might be able to prevent or delay cognitive decline.
Several tests exist, but they are expensive, rely on specialized equipment and can only detect a few biomarkers at a time. By contrast, 5ADCSI can measure five key Alzheimer’s biomarkers and relies on xMAP® technology, a widely available system from the biotechnology company Luminex...
The full paper is here: High precision and cost-effective multiplex quantification of amyloid-β40, amyloid-β42, p181Tau, p217Tau, neurofilament light chain, and glial fibrillary acidic protein from plasma and serum
These are ligand binding tests on a multiplex (Luminex) instrument. I'm not a ligand binding kind of guy, even though my first job was making radiolabeled ligand binding tests. (RIA, a largely extinct technology now). Still the multiplex should eliminate false positives, to a large extent. We'll have to see how this develops.
I'm not quite sure how accurately the test can measure conformational differences, which is how I understand the tau issue, similar to prion disease, albeit although it would be unsurprising if it did so. There are modern mass spec tools that can address conformation, technology known as IMS, but I'd admit they'd be difficult and expensive to use.
There's no treatment, of course, really, so I'm not sure I'd want to know.
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