The FDA cleared PrecivityAD2, a blood test from C2N Diagnostics, on August 20, 2026, making it the first FDA-cleared Alzheimer's blood test authorized for adults as young as 40 who show signs of cognitive impairment, according to C2N Diagnostics' press release. For people with mild cognitive impairment (MCI), the test can flag whether amyloid plaque is likely present, but it does not tell them whether that plaque will progress to Alzheimer's disease or what to do about it if it has. The clearance is real and specific, not a general screening approval. It applies only to adults already undergoing clinical evaluation for cognitive decline, and the FDA requires it to be used alongside a clinician's assessment rather than on its own, as Healio reported.
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Table of Contents
- What PrecivityAD2 Measures and How It Works
- How Accurate Is the Test, and Who Gets an Unclear Result?
- Why Mild Cognitive Impairment Changes the Picture
- How PrecivityAD2 Compares to Other Cleared Blood Tests
- What This Means for Someone With MCI Considering the Test
- Frequently Asked Questions
What PrecivityAD2 Measures and How It Works
PrecivityAD2 is a blood test, not a brain scan or spinal tap. It uses high-resolution mass spectrometry to measure two ratios in a blood sample: amyloid-beta 42/40 and p-tau217/np-tau217. These are proteins tied to the buildup of amyloid plaque, one of the physical changes seen in Alzheimer's brains. The two ratios are combined into a single score C2N calls the Amyloid Probability Score 2, or APS2, as described by NeurologyLive.
This mass spectrometry approach sets PrecivityAD2 apart from earlier competitor blood tests, which rely on immunoassay technology, a different lab method for detecting proteins. The distinction matters mainly to clinicians choosing between tests, but it is part of why C2N markets PrecivityAD2 as a more precise readout of amyloid status. A positive, negative, or intermediate APS2 result corresponds to the biological presence of amyloid plaque, not to a diagnosis of Alzheimer's disease by itself. A clinician still has to interpret that result alongside memory testing, a neurological exam, and the person's history and symptoms.
How Accurate Is the Test, and Who Gets an Unclear Result?
In the FDA's clearance study of 1,142 symptomatic adults, a positive APS2 result predicted amyloid pathology correctly 97.6% of the time, and a negative result ruled it out correctly 93.1% of the time, benchmarked against amyloid PET scans or spinal fluid testing, according to the Alzheimer's Drug Discovery Foundation. Those numbers hold up well for people who land in a clear positive or clear negative range. The gap is the group in between.
About 17.3% of study participants fell into an intermediate "likely positive" category, and that category's positive predictive value drops to 77.3%, substantially less reliable than a clear reading, per NeurologyLive's coverage. In practice, that means roughly one in six people tested gets a result that does not clearly confirm or rule out amyloid plaque. A separate validation using the ADNI research cohort, an independent Alzheimer's research dataset, compared APS2 against amyloid PET scans in cognitively impaired patients and found accuracy, sensitivity, and specificity each at or above roughly 90%, reported by global neurology coverage. That study reused the cut point C2N had already set rather than building a separate threshold specifically for MCI patients, so its strong numbers describe the existing score applied to an MCI-heavy group, not a version tuned for MCI alone.
Why Mild Cognitive Impairment Changes the Picture
Mild cognitive impairment describes a stage where a person has noticeable memory or thinking problems beyond normal aging, but can still function independently day to day. Some people with MCI go on to develop Alzheimer's disease; others do not. A blood test that detects amyloid plaque answers one question about someone with MCI: is amyloid present. It does not answer whether that person's MCI will progress to dementia, or when.
A 2022 review in American Family Physician looked at the original PrecivityAD test, the direct predecessor to PrecivityAD2, and found it correlated with amyloid PET scans in older adults with MCI. But the review concluded that the test's actual role and accuracy for diagnosing or predicting the progression of Alzheimer's disease in MCI patients remained unknown, and that scores falling in an indeterminate range had unclear clinical meaning, according to American Family Physician. That open question about predicting progression has not been resolved by the newer APS2 score; the available validation data confirms amyloid detection accuracy, not progression forecasting. The same review raised a practical concern that still applies: because high-quality evidence for treatments that prevent or delay Alzheimer's onset in people with MCI is still limited, a positive amyloid result in someone with MCI can create anxiety or pressure toward treatment without a clear next clinical step to follow it with, per the same American Family Physician review.
How PrecivityAD2 Compares to Other Cleared Blood Tests
PrecivityAD2 is the third FDA-cleared blood-based Alzheimer's biomarker test overall, and the first one cleared for adults starting at age 40. Earlier cleared tests, including Fujirebio's Lumipulse, cleared through the FDA's 510(k) pathway in May 2025, set their age floor at 55 and older, according to the Alzheimer's Association.
That lower age threshold means younger adults with cognitive symptoms now have an FDA-cleared blood-based option where none existed before. The lower age floor does not change what the test can tell a younger patient: it still only reports amyloid status, interpreted alongside a clinical evaluation, regardless of the patient's age. A younger adult with MCI faces the same interpretive gap around progression that an older adult does.
What This Means for Someone With MCI Considering the Test
A person with MCI weighing this test, or a family member helping them decide, can use a few practical points to frame the conversation with a clinician:.
- The test can be ordered starting at age 40 for someone already being evaluated for cognitive symptoms, not as a routine screening for people without symptoms.
- A clear positive or negative result is highly reliable for detecting amyloid plaque; an intermediate "likely positive" result, which happens in roughly one of every six people tested, carries meaningfully less certainty.
- A positive result confirms amyloid is present. It does not predict how fast MCI will progress or whether it will progress to Alzheimer's disease at all.
- The result is meant to be interpreted by a clinician alongside cognitive testing and clinical history, not read on its own.
- Asking a clinician in advance what specific result would change the care plan can clarify whether testing now will lead to a concrete next step, rather than a number without a clear action attached to it.
Frequently Asked Questions
Does a positive PrecivityAD2 result mean someone with MCI will develop Alzheimer's disease?
No. It confirms amyloid plaque is likely present, but the available evidence does not establish how reliably that predicts progression from MCI to Alzheimer's disease.
Can someone without cognitive symptoms request this test as a screening tool?
No. The FDA's clearance covers adults 40 and older who are already undergoing clinical evaluation for cognitive decline, not general screening.
What happens if someone gets an intermediate or "likely positive" result?
That result carries a 77.3% positive predictive value, notably less certain than a clear positive or negative reading, so a clinician would typically weigh it alongside other clinical findings rather than treat it as conclusive.
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