The Result Came Back. Now What?

The test is the easy part now. A negative result rules out Alzheimer's pathology. A positive one points to amyloid, still needs confirming, and is not yet a diagnosis.

What does a positive result actually mean?

That amyloid is probably present in her brain. It does not establish that she has Alzheimer's disease, and it says nothing about what stage she is in.

The current blood tests measure phosphorylated tau 217, sometimes alongside amyloid beta. They are proxies — they estimate how likely it is that amyloid plaques would be found if you scanned her brain.

Three things a positive result does not tell you:

• It does not tell you she has dementia. Dementia is defined by function — whether cognitive changes are interfering with daily life. That is determined by history and examination, not by a lab value.
• It does not tell you what stage she is in. Staging comes from what she can and cannot do now.
• It does not tell you her symptoms come from amyloid. Someone can have amyloid pathology and have her memory problems driven by something else entirely, or by several things at once.

That last point has a number attached to it. A meta-analysis of individual participant data found the prevalence of amyloid pathology among people with normal cognition climbed from 10% at age 50 to 44% at age 90. Nearly half of cognitively healthy ninety-year-olds would test positive. A positive result in an eighty-five-year-old is therefore much weaker evidence than the same result in a sixty-year-old with clear symptoms.

Does a positive result need to be confirmed?

Under the current guideline, yes. A negative result rules the pathology out; a positive one is meant to be confirmed with amyloid PET or spinal fluid analysis.

The Alzheimer's Association published its first clinical practice guideline on blood-based biomarkers in July 2025, in Alzheimer's & Dementia. For patients with objective cognitive impairment presenting to specialized memory care, the panel suggested using a high-sensitivity blood test as a triaging test — a conditional recommendation based on low-certainty evidence.

The guideline treats the two results differently. A negative result is treated as sufficient to rule out Alzheimer's pathology. A positive result is treated as a reason to go on and confirm, with amyloid PET imaging or cerebrospinal fluid analysis from a lumbar puncture. The performance bar the guideline sets — greater than 90% sensitivity and greater than 75% specificity — is deliberately built that way: catch everyone who has it, accept that some positives will be wrong.

So "her blood test was positive for Alzheimer's" is a sentence that has skipped a step. The right question at the next appointment is whether confirmation is planned, and if not, why not. Sometimes there is a good reason — the clinical picture is unambiguous, or confirmation would not change anything anyone intends to do. That reason should be said out loud rather than assumed.

What if the result says "intermediate"?

It means the test could not classify her. It is not a mild case and it is not half a diagnosis.

Both FDA-cleared tests report three categories rather than two. Fujirebio's Lumipulse, cleared in 2025 for specialized care, reports negative, intermediate or positive. Roche's Elecsys pTau217 plasma test, developed with Eli Lilly and cleared in August 2026 for use in both primary and specialty care in people aged 55 and over with signs or symptoms of cognitive decline, uses the same three categories.

An intermediate result is a statement about the test, not about her. Her value fell in a range where the assay cannot reliably separate amyloid-positive from amyloid-negative. The next step is a different test — PET or spinal fluid — not a repeat of the same blood draw and not a wait-and-see.

If an intermediate result is being treated as a soft yes or a soft no, that is worth pushing back on.

What if it came back negative?

Then Alzheimer's pathology is unlikely, and the symptoms still need an explanation. This is where workups most often stop, and where they should not.

A negative result is genuinely informative — under the guideline it is the result you can lean on. But it answers only one question, and the person in front of you still cannot remember the conversation from this morning.

What remains on the table:

• Vascular cognitive impairment — damage from small strokes and small vessel disease, often visible on MRI.
• Lewy body dementia — where visual hallucinations, acting out dreams, fluctuating alertness and parkinsonian movement changes matter more than memory.
• Frontotemporal dementia — where personality change, loss of social judgment or language difficulty comes first, often before age 65.
• Depression — common, treatable, and mistaken for early dementia often enough that it belongs on every list.
• Sleep apnea — untreated, it produces daytime cognitive impairment that improves with treatment.
• Medication effects — anticholinergics, sedatives, sleep aids and bladder drugs among them.
• Thyroid disease and B12 deficiency — standard, cheap, worth doing.

Ask directly: "If it isn't Alzheimer's, what is next in the workup?" A negative biomarker plus no further plan is an unfinished evaluation.

Who should be interpreting this?

A specialist, in most cases. The newest test is cleared for primary care use, which makes the referral question more urgent rather than less.

Until recently, these tests lived in memory clinics. The August 2026 clearance of the Elecsys pTau217 test extended cleared use into primary care, which means far more results will now be delivered by clinicians who see dementia occasionally rather than daily.

That is not an argument against the test. Earlier evaluation is the single thing most likely to help a family. It does mean the referral matters. Reasonable asks:

• A referral to a memory clinic, behavioral neurologist, geriatrician or geriatric psychiatrist. Ask for it at the visit where the result is given, because wait times are frequently measured in months.
• A structured cognitive assessment if one has not been done — the blood test does not replace it.
• Brain imaging. An MRI shows vascular damage, atrophy patterns and the occasional treatable surprise, none of which a blood test can see.
• A copy of everything for the next clinician, so the workup does not restart from zero.

Does a positive result qualify her for the new drugs?

Not by itself. Eligibility for lecanemab or donanemab turns on stage, confirmed amyloid, genetic testing and imaging, and most people evaluated do not qualify.

The anti-amyloid infusions are approved for early symptomatic disease — mild cognitive impairment or mild dementia due to Alzheimer's. Someone already in moderate or later-stage dementia is outside that window regardless of what any test says.

Beyond stage, the pathway involves confirmed amyloid pathology, APOE genotyping to assess the risk of ARIA (swelling and small bleeds in the brain seen on MRI), a baseline MRI, and ongoing MRI monitoring during treatment. It is a serious program with real risks, and it is not a consequence of a blood test result.

If treatment is the reason for the testing, say so early. It changes the urgency of the referral, because eligibility depends on stage and stage depends on time.

What should we do in the next month, whatever the result says?

The planning that matters most does not depend on confirmation, and it gets harder every month it waits.

• Powers of attorney — financial and healthcare — while she can still sign. Capacity is required to grant them. Once it is gone, the alternative is guardianship, which is slower, public and expensive.
• A healthcare proxy and a conversation about what she would want. Not a form. A conversation, and then a form.
• A medication review with a pharmacist. Anticholinergics, sedatives and sleep aids can all be making her worse right now, and this is the fastest available win.
• The driving question. It is the hardest conversation and the one most often postponed until an incident forces it.
• A financial picture. Where the money is, who can reach it, what insurance exists.
• Who to tell, and when. Her decision to make while she can make it.

What questions should I bring to the next appointment?

Ask what the result was exactly, what confirms it, and what happens next in either direction.

• "What was the actual value, and which category — positive, intermediate or negative?"
• "Which test was used?"
• "Is confirmation with PET or spinal fluid planned? If not, why not?"
• "What else could be contributing, and how would we check?"
• "Has she had an MRI?"
• "What stage would you say she is in, and what are you basing that on?"
• "Who is the specialist, and how long is the wait?"
• "What should we do in the meantime?" — the answer should include the legal and medication items above.