The headline undersold it. The New York Times called this "new promise" on July 15. Fujirebio's Lumipulse G pTau217/β-Amyloid 1-42 plasma ratio had been running in clinics for over a year by then, FDA-cleared in May 2025 and available through Labcorp and Quest Diagnostics.
92% right when it says yes. In the 499-patient study behind that clearance, a positive result meant amyloid pathology was present 92% of the time. A negative result cleared it with 97% confidence. Getting numbers like that used to mean a PET scan or a spinal tap.
One test doesn't make a diagnosis. A positive p-tau217 result means amyloid is probably there. A neurologist still weighs it against cognitive testing and clinical history before anyone says the word Alzheimer's.
A second test moved this into primary care. The FDA cleared Roche's Elecsys pTau181 on October 13, 2025 for use in the primary care setting, in adults 55 and older with signs, symptoms or complaints of cognitive decline. It works as a rule-out, reporting a 97.9% negative predictive value in the study behind the clearance. Labcorp made it available nationwide on February 11, 2026 across more than 2,200 patient service centers. A primary care clinician can order it, with no specialist referral in between.
Symptoms are the gate. All four cleared indications start from a patient who already has signs, symptoms or complaints of cognitive decline. Memory complaints, word-finding trouble, a family pushing for answers: that is the path to getting any of the four tests ordered. For someone with no symptoms at an annual physical, none of the four biomarkers is on anyone's radar. The setting question has been answered for three of them now. The symptom requirement has not moved for any.
A third test dropped the age floor to 40. The FDA cleared C2N Diagnostics' PrecivityAD2 on August 20, 2026, for adults as young as 40 with signs of cognitive impairment, well below the 55-and-older floor both Lumipulse and Elecsys pTau181 share. It runs on high-resolution mass spectrometry, measuring the same class of amyloid and p-tau ratios, and reported a 97.6% positive predictive value and a 93.1% negative predictive value in a 1,142-subject validation study. Someone in their 40s with real cognitive symptoms now has a cleared blood test option that did not exist two weeks ago.
A fourth test collapses two assays into one. The FDA cleared Roche and Eli Lilly's Elecsys pTau217 on August 24, 2026, for adults 55 and older with cognitive decline. What makes it different isn't the biomarker (Fujirebio's Lumipulse already measures p-tau217, as part of a ratio with amyloid), it's the single-cutoff design: one biomarker, one validated cutoff, usable to both rule in and rule out amyloid pathology, in primary care or specialty care. Every prior cleared test needed either a different assay or a setting-specific read. Roche calls it the "Power of One." It runs on the more than 4,500 Roche cobas analyzers already installed in US labs, and Labcorp and Quest both said they will offer it.
Updated August 19, 2026. This post originally ran on July 28 arguing that an Alzheimer's blood test existed but could not be ordered outside a specialist setting. That was wrong on two counts. Roche's primary-care clearance predated the post by nine months and Labcorp's nationwide rollout predated it by five, so a GP could already order one. The post also gave the Lumipulse age indication as 50 and older, where the FDA clearance says 55 and older. Both are corrected above.
Updated August 22, 2026. A third FDA-cleared test now exists. The count above is updated from two to three throughout this post to reflect PrecivityAD2's clearance. See the full story on PrecivityAD2's age-40 clearance for the validation numbers and what changed.
Updated August 27, 2026. A fourth FDA-cleared test now exists. The count above is updated from three to four throughout this post to reflect Elecsys pTau217's clearance. See the full story on pTau217's single-cutoff clearance for what changed and why it's a different milestone than Roche's earlier pTau181 test.
Cognitive symptoms like brain fog or word-finding trouble sent you looking at blood tests in the first place? None of the three p-tau tests will be on a standard panel. See blood test markers for brain fog for what your panel checks first.