Four Days. Two FDA Clearances. One Inflection Point for Alzheimer’s Diagnosis.

In late August 2026, two very different Alzheimer’s blood tests crossed the FDA threshold. The opportunity is enormous, but only if access is matched by clinical judgment.

Four days. Two FDA clearances. One unmistakable signal: Alzheimer’s blood testing is moving from promising specialty science toward scalable clinical infrastructure.

On August 20, 2026, the FDA cleared C2N Diagnostics’ PrecivityAD2® blood test. On August 24, the agency cleared Roche and Eli Lilly’s Elecsys® Phospho-Tau (217P) Plasma assay.

These were clearances, not drug approvals, and they were not the first FDA clearance in this category. Fujirebio’s Lumipulse blood test reached that milestone in May 2025. But two additional clearances within four days deserve attention because they expand the range, reach and practicality of blood-based Alzheimer’s assessment in distinctly different ways. This is not simply “another lab test.” It may change who can begin an Alzheimer’s evaluation, how quickly patients can move through it and when specialists become involved.

Two tests. Two architectures. One clinical target.

PrecivityAD2: a multi-analyte, mass-spectrometry approach

PrecivityAD2 uses high-resolution mass spectrometry to measure the plasma amyloid-beta 42/40 ratio and the ratio of phosphorylated tau 217 to non-phosphorylated tau 217. Those results are combined into the Amyloid Probability Score 2, or APS2.

The FDA-cleared test is indicated for adults 40 years and older who have signs or symptoms of cognitive impairment and are being evaluated for Alzheimer’s disease or another cause of cognitive decline. This is the youngest indicated population for any FDA-cleared Alzheimer’s blood test to date.

In C2N’s 1,142-person clinical validation cohort, the company reported a 97.6% positive predictive value for a Positive result and a 93.1% negative predictive value for a Negative result against amyloid PET or cerebrospinal-fluid reference testing. A separate “Likely Positive” category accounted for 17.3% of results and had a 77.3% positive predictive value.

Elecsys pTau217: one biomarker, fully automated

Roche’s assay takes a different route. It measures plasma pTau217 alone through a fully automated electrochemiluminescence immunoassay and reports Positive, Intermediate or Negative categories.

It is indicated for adults 55 years and older with signs, symptoms or complaints of cognitive decline. It is the first FDA-cleared single-biomarker blood test designed to support both rule-in and rule-out assessment of amyloid pathology using the same validated cutoffs in primary and specialty care. Its potential scale is striking: the assay is designed to run on more than 4,500 Roche cobas laboratory instruments already installed across the United States. Labcorp has announced a nationwide rollout in the coming months, and Quest plans to introduce a service based on the assay in the fourth quarter of 2026. It is tempting to ask which test “won.” That is the wrong question. The clinically important question is: Which validated assay fits this patient, this setting and the decision that must come next?

Why primary care and psychiatry should pay close attention

Patients rarely begin by saying, “I may have amyloid pathology.” They report forgetfulness. Repeated questions. Trouble managing finances. Loss of efficiency at work. Word-finding difficulty. New apathy, anxiety or irritability. An apparent recurrence of attention problems. Sometimes the first concern is raised in primary care; sometimes in psychiatry; sometimes during a discussion about sleep, menopause, medications or metabolic health. Until recently, a biologically informed Alzheimer’s evaluation often depended on specialty access, amyloid PET imaging or lumbar puncture. Blood-based biomarkers can reduce that friction.

In a 2024 prospective JAMA study of 1,213 symptomatic patients, the APS2 blood test achieved diagnostic accuracy of approximately 88% to 92% across primary- and secondary-care cohorts. In that study, the blood test outperformed clinicians’ standard evaluations performed without Alzheimer’s biomarkers. Preliminary real-world data presented at the 2026 Alzheimer’s Association International Conference further suggested that access to blood-test results brought primary-care and specialist diagnostic accuracy to approximately 90%. That does not make the clinician less important. It makes the clinical question more consequential.

A blood biomarker can identify a high or low likelihood of Alzheimer-associated amyloid pathology. It cannot, by itself, determine why a particular patient is cognitively impaired.

A positive result does not prove that Alzheimer’s disease is the sole, or even primary, cause of a patient’s symptoms. Amyloid pathology can coexist with vascular brain injury, Lewy body disease, frontotemporal degeneration, limbic-predominant age-related TDP-43 encephalopathy, sleep apnea, depression, medication effects and other contributors. A negative result does not mean that the patient’s symptoms are benign. It should redirect the evaluation toward non-Alzheimer causes of cognitive decline. An intermediate or “Likely Positive” result is not diagnostic limbo. It is a signal that the next step may require specialist interpretation, repeat assessment, amyloid PET, cerebrospinal-fluid biomarkers or another targeted evaluation.

And an age indication is not the same as universal appropriateness. In a symptomatic patient in their 40s, for example, the pretest probability and differential diagnosis may be very different from those of an older patient in a memory clinic. Predictive values change with the population being tested.

The Alzheimer’s Association clinical practice guideline therefore emphasizes a comprehensive clinical evaluation, objective cognitive impairment and attention to pretest probability. It also cautions that assay performance varies and that many commercial tests have not met the same performance thresholds.

A practical message for clinicians

The new rule should be simple: Do not order a biomarker that you are not prepared to interpret, disclose and act upon.

Before testing, establish the clinical phenotype. Obtain collateral history when possible. Assess function and objective cognition. Review sleep, mood, medications, vascular and metabolic risk, hormonal context and other potentially reversible contributors. Use structural brain imaging and additional testing when indicated.

Refer promptly when:

• cognitive or functional decline is progressive or corroborated by family;

• the presentation is young-onset, atypical or diagnostically discordant;

• language, behavior, executive function or visuospatial ability is changing;

• a blood biomarker is positive, intermediate or inconsistent with the clinical picture;

• symptoms continue to progress despite a negative Alzheimer biomarker; or

• the patient may be a candidate for disease-modifying therapy.

Even a strongly positive blood biomarker is only one component of treatment evaluation. Anti-amyloid therapy requires separate assessment of disease stage, functional status, brain MRI findings, hemorrhagic and ARIA risk, APOE genotype, medications, including anticoagulants, and the patient’s goals and ability to complete ongoing safety monitoring.

The real breakthrough is not the blood draw

The breakthrough is the possibility of shortening the distance between concern and a defensible clinical answer. But as testing becomes easier, interpretation becomes the new bottleneck. The health systems and clinicians who succeed will be those who build a pathway around the result: appropriate patient selection, informed consent, precise interpretation, timely referral and an actionable plan.

Primary care and psychiatry are not peripheral to this transition. They are the front door. Neurology must be ready to meet them there.

About the author

Myrna Cardiel, MD, is a board-certified neurologist, former NYU Langone Clinical Professor of Neurology and founder of Cardiel Precision Brain Health in Manhattan. Her practice provides comprehensive, individualized care for cognitive concerns, brain health, migraine and the neurologic effects of sleep, hormonal and metabolic change.

At Cardiel Precision Brain Health in Manhattan, I provide timely, neurologist-led evaluation of progressive memory, language, attention, executive and other cognitive concerns, including cases in which mood, sleep, menopause, metabolic health or medication effects complicate the picture. I welcome referrals from colleagues who need help deciding whether a blood biomarker is appropriate, interpreting a result or determining the next step toward diagnosis and treatment. The blood test is not the diagnosis. Used well, it may finally help us reach the right diagnosis sooner.

This article is for professional education. Mention of specific assays is not a product endorsement and does not replace individualized clinical assessment.

Bibliography

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