New Alzheimer’s Blood Test Accuracy Rates

Diagnosing Alzheimer’s disease has historically been a complex, expensive, and invasive process. For years, patients relied on subjective cognitive exams, costly PET scans, or painful lumbar punctures to get answers. However, a major shift is happening in neurology. New blood tests capable of detecting specific biomarkers are showing accuracy rates that rival these gold-standard methods. This development transforms how early pathology is detected and makes access to new treatments feasible for more people.

The Breakthrough Biomarker: p-tau217

The surge in accuracy for these new diagnostic tools centers on a specific protein called phosphorylated tau 217, or p-tau217. While older blood tests looked for amyloid-beta (which could be inconsistent in blood samples), p-tau217 is a highly specific marker of the brain changes associated with Alzheimer’s disease.

A major study published in JAMA Neurology in January 2024 highlighted the effectiveness of this biomarker. Researchers evaluated a commercial blood test from ALZpath and found that it could identify biological signs of Alzheimer’s with high precision.

Key Accuracy Statistics

Amyloid Detection: The p-tau217 blood test demonstrated up to 96% accuracy in identifying elevated beta-amyloid levels in the brain.
Tau Pathology: It showed up to 97% accuracy in detecting tau tangles.
Comparison: These rates are statistically comparable to cerebrospinal fluid (CSF) tests derived from spinal taps, which have long been considered the most accurate biological confirmation method.

Leading Tests and Manufacturers

Several biotechnology companies are racing to bring these tests to the commercial market. While you cannot simply buy these at a local pharmacy, specialists are beginning to order them to screen patients with memory complaints.

C2N Diagnostics: PrecivityAD2

One of the most prominent tests currently available is the PrecivityAD2 test by C2N Diagnostics. This is a second-generation test that improves upon their earlier model.

Method: It uses mass spectrometry to measure the ratio of tau proteins and amyloid proteins.
Performance: Clinical validation studies indicate an accuracy of roughly 90% when compared to amyloid PET scans.
Status: It is currently available as a “Laboratory Developed Test” (LDT) under CLIA regulations. Doctors can order it, and the sample must be sent to C2N’s specific lab in St. Louis.

Quanterix: LucentAD

Quanterix has developed the LucentAD p-Tau 217 test. This test runs on their Simoa platform, which is known for being ultra-sensitive to low levels of proteins in the blood.

Focus: It is designed to rule out Alzheimer’s pathology in patients presenting with cognitive decline.
Validation: In studies comparing the test against amyloid PET status, the diagnostic accuracy (AUC) was reported at approximately 0.94 (on a scale where 1.0 is perfect).

Roche and Eli Lilly

Pharmaceutical giants are also involved. Roche is developing the Elecsys Amyloid Plasma Panel, which recently received FDA Breakthrough Device Designation. Eli Lilly (the maker of the Alzheimer’s drug Kisunla) has collaborated with Quanterix and others to ensure testing is available to identify patients who qualify for their treatments.

Cost and Accessibility vs. Traditional Methods

The primary driver for these blood tests is accessibility. Traditional diagnostic routes create bottlenecks that delay treatment.

PET Scans:

Cost: Typically between $5,000 and $7,000.
Availability: Limited to major medical centers.
Drawback: Exposure to radiation and requires long appointment times.

Lumbar Punctures (Spinal Taps):

Cost: Generally $800 to $1,500.
Drawback: Invasive, painful, and often causes headaches or back pain, leading to patient refusal.

Blood Tests (p-tau217):

Cost: Currently ranges from $200 to $500.
Availability: Can be drawn at a standard phlebotomy lab or doctor’s office.
Advantage: Scalable. Millions of people can be screened quickly compared to the limited slots available for PET scanners.

The Role of FDA Approval

It is important to understand the regulatory status of these tests. As of early 2024, most of these specific p-tau217 tests are available as LDTs (Laboratory Developed Tests). This means the specific lab performing the test has validated it, but the test kit itself has not yet received full, broad marketing clearance from the FDA for sale to other labs.

However, the FDA is actively reviewing these devices. The “Breakthrough Device Designation” granted to Roche and Quanterix suggests the FDA views these tests as critical for public health. Full approval will likely standardize the scoring systems across different brands, making it easier for primary care doctors to interpret results without consulting a neurologist.

Why High Accuracy Matters Now

The timing of these high-accuracy tests coincides with the approval of disease-modifying therapies. Drugs like Leqembi (lecanemab) and Kisunla (donanemab) work by removing amyloid plaque from the brain.

To prescribe these drugs, doctors must confirm that the patient actually has amyloid plaques. Giving these strong medications to someone with a different form of dementia (like Frontotemporal Dementia) would be useless and potentially dangerous. The 90%+ accuracy of p-tau217 blood tests allows physicians to prescreen patients efficiently. Those with negative blood tests can avoid expensive PET scans, while those with positive results can move forward to treatment confirmation much faster.

Frequently Asked Questions

Can I ask my primary care doctor for this test?

Technically, any licensed physician can order tests like the PrecivityAD2. However, many primary care doctors are not yet familiar with interpreting the results. It is currently more common for neurologists or memory specialists to order them.

Does insurance cover Alzheimer’s blood tests?

Coverage is currently inconsistent. Medicare does not broadly cover these specific blood tests for screening yet, though they cover the follow-up PET scans or spinal taps in many cases. Patients often pay out-of-pocket, with costs ranging from $200 to $500 depending on the provider.

Are false positives possible?

Yes. While accuracy is high (around 95%), false positives can happen. This is why doctors may still use a “grey zone” or intermediate result range. If a blood test result is borderline, the doctor will likely recommend a PET scan or spinal tap to be 100% certain before starting heavy medication.

How early can these tests detect Alzheimer’s?

Research suggests that p-tau217 levels begin to rise in the blood up to 15 to 20 years before symptoms like memory loss appear. However, clinical use is currently focused on patients who are already showing signs of cognitive impairment, rather than predicting the disease in healthy young people.