FDA-cleared blood tests that look for the brain changes of Alzheimer’s disease now exist, but they are meant for adults who already have memory or thinking problems and are being evaluated by a clinician, not for healthy people who want to know their future risk. The tests track amyloid-beta, a short protein fragment that clumps into the plaques that define the disease, along with a related tau marker. If you or a parent is noticing memory changes, the useful step is a full evaluation; a blood test can be one part of it, not a shortcut around it.
What the blood tests actually measure
Amyloid plaques are made mainly of amyloid-beta peptides 40 and 42 amino acids long, cut from a larger protein called amyloid precursor protein, as described in a 2026 multicenter validation study in Alzheimer’s & Dementia and in the UniProt record for that precursor. The study notes that the 42-amino-acid form is the one that aggregates into insoluble plaques. Blood tests use these peptides, or a phosphorylated form of the tau protein called p-tau217, as indirect signs of whether plaques are present in the brain.
In May 2025 the FDA cleared the first such blood test, Fujirebio’s Lumipulse ratio of p-tau217 to amyloid-beta 1-42, for adults 55 and older with signs and symptoms of cognitive decline who are seen in specialized care. In the 499-person study the agency reviewed, 91.7 percent of people with a positive result had amyloid plaques on a brain scan or spinal fluid test, 97.3 percent of those with a negative result did not, and just under 20 percent got an indeterminate result that needs more testing. In August 2026 Roche announced FDA clearance of its Elecsys p-tau217 blood test for people 55 and older with signs, symptoms or complaints of cognitive decline, for use in both primary and specialty care, with positive, intermediate and negative result categories.
Who the tests are for, and who they are not for
The FDA said plainly that the Lumipulse test is not intended as a screening or stand-alone diagnostic test. It also named the main risks: a false positive could lead to a wrong diagnosis, distress and unnecessary treatment, while a false negative could delay the right care.
The Alzheimer’s Association’s 2025 clinical practice guideline is narrower still. It covers only people with measurable cognitive impairment who are being worked up by clinicians experienced in memory disorders, and it does not extend to people without cognitive symptoms. It sets accuracy bars: a test needs at least 90 percent sensitivity and 75 percent specificity to be used for triage, and at least 90 percent for both to stand in for a brain scan or spinal tap. The panel warned that many commercially available tests do not meet those thresholds, that patients and clinicians should not assume different tests are interchangeable, and that direct-to-consumer versions can cause confusion and unwarranted anxiety.
Primary care use is still debated. A 2026 Personal View in Neurology argued that, until clearer guidance and care pathways exist, use outside specialist settings should stay selective and tied to a real clinical question.
Things that can throw off a result
The guideline lists situations where results need extra care, including severe chronic kidney disease, a recent acute brain injury, ALS, and certain medicines such as neprilysin inhibitors, a class that includes the heart failure drug sacubitril. The 2026 validation study adds that kidney clearance may influence p-tau217 levels. Telling the clinician about kidney function and every medicine you take helps them read the number correctly.
How to use this at the appointment
- Bring a written timeline of the memory or thinking changes and examples from daily life; the guideline says blood tests do not replace a full clinical evaluation.
- Ask which test would be used, whether it meets the guideline’s accuracy thresholds, and what happens after an intermediate result.
- Ask how a positive or negative result would change the plan, since an amyloid result points to one possible cause of symptoms rather than a complete diagnosis.
- If you have no symptoms, be wary of paying for a test online: the FDA clearances and the guideline described here cover only people who already have symptoms.
By The Everyday Brief · AI-assisted editorial. Drafted with AI research assistance; claims checked against the linked sources (fetched 2026-10-07 PT). Not medical advice.
Sources
- U.S. FDA: FDA Clears First Blood Test Used in Diagnosing Alzheimer’s Disease (May 16, 2025)
- Roche Diagnostics: Roche receives FDA clearance for Elecsys pTau217 (August 24, 2026; company announcement)
- Palmqvist S, et al. Alzheimer’s Association Clinical Practice Guideline on the use of blood-based biomarkers in the diagnostic workup of suspected Alzheimer’s disease within specialized care settings. Alzheimer’s & Dementia, 2025.
- Moghekar AR, et al. Multicenter validation of plasma p-tau217/amyloid beta 1-42 ratio in symptomatic Alzheimer’s disease. Alzheimer’s & Dementia, 2026.
- Hazan J, et al. Blood-Based Biomarkers for Alzheimer Disease in Primary Care: The Gap Between Biology and Clinical Utility. Neurology, 2026.
- UniProt: Amyloid-beta precursor protein, including amyloid-beta 40 and 42 (P05067)