New Study Demonstrates Accuracy of Two Quest AD-Detect® Tests for Alzheimer's Disease Diagnosis

Rhea-AI Summary

Quest Diagnostics (NYSE: DGX) published a study showing two AD-Detect blood-test panels accurately identify Alzheimer’s pathology in symptomatic patients. In an intended-use cohort of 215 patients (46% amyloid PET-positive), both panels met a 91% sensitivity and 91% specificity threshold used for confirmatory testing. The three-biomarker panel (AB42/40 + p-tau217 + ApoE4) yielded PPV 88%, NPV 91% and a 10% indeterminate rate. The two-biomarker panel (AB42/40 + p-tau217) showed PPV 87%, NPV 91% and a 15% indeterminate rate. Quest launched the two-biomarker panel in April 2025 and plans a version of the three-biomarker test in Q1 2026.

Results meet recommended thresholds from Alzheimer's Association and CEOi for confirmatory blood-based tests, suggesting potential to reduce reliance on PET or CSF follow-up.

Positive

• Sensitivity 91% in intended-use symptomatic cohort
• Specificity 91% in intended-use symptomatic cohort
• PPV 88% for three-biomarker panel at 46% prevalence
• NPV 91% for both panels
• 10% indeterminate rate for three-biomarker panel (meets CEOi guidance)
• Two-biomarker panel launched April 2025; three-biomarker version planned Q1 2026

Negative

• Indeterminate 15% for two-biomarker panel (near CEOi upper limit)
• Predictive values depend on prevalence; PPV may decline in lower-prevalence settings
• p-tau217 measured via third-party immunoassay, not proprietary method

Insights

Clinical diagnostic strategist

Quest's blood-based AD-Detect panels meet recommended diagnostic thresholds and could reduce need for PET/CSF confirmation.

The tests combine circulating biomarkers (AB 42/40 and p-tau217, with an optional ApoE4 proteotype) to produce a likelihood score that aligns with guideline targets of ~90% sensitivity and 90% specificity; the three-marker panel reported 91% sensitivity, 91% specificity, 88% PPV and 91% NPV in an intended-use sample where 46% were amyloid PET-positive, indicating the assay operates at the performance bar set by clinical groups for confirmatory blood testing.

Practical value depends on real-world prevalence, test reproducibility, and workflow adoption. Predictive values will vary by population prevalence; the reported indeterminate rates (10% with ApoE4, 15% without) fall within recommended limits but still leave a measurable fraction requiring further testing. The methods mix proprietary tandem mass spectrometry for AB 42/40 and ApoE4 with a third-party immunoassay for p-tau217, so lab-to-lab consistency and assay supply chain stability are relevant operational risks.

Watch for commercial rollout and independent validation: the company plans a version launch in Q1 2026, and prior data were presented at AAN in April 2025. Key near-term items to monitor are real-world indeterminate rates across care settings, peer-reviewed replication of the 91%/91% performance in larger cohorts, and clinical adoption metrics over the first 6–12 months post-launch.

The Quest AD-Detect® blood-based test panels deliver confirmatory accuracy, potentially supporting reduced reliance on PET-imaging confirmation

SECAUCUS, N.J., Oct. 27, 2025 /PRNewswire/ -- Two blood tests, each involving multiple biomarkers, are highly accurate at identifying Alzheimer's disease pathology in symptomatic patients, supporting diagnosis, according to a new study in Neurology® Clinical Practice, a publication of the American Academy of Neurology.

Conducted by scientists with Quest Diagnostics (NYSE: DGX) and 1Florida ADRC, University of Florida, the study suggests both tests may fulfill guideline-based criteria for confirming Alzheimer's disease without follow-up tests, such as amyloid positron emission tomography (PET) scan or cerebrospinal fluid (CSF) tests.

"This study demonstrates that scalable blood-based testing can meet rigorous standards for establishing Alzheimer's disease pathology, supporting diagnosis and advancing patient care for Alzheimer's disease in the intended use patients," said Michael Racke, MD, a board-certified neurologist and Senior Medical Director of Neurology, Quest Diagnostics. "Our analysis also suggests that blood-based testing can achieve a rate of indeterminate, or unclear, results, as low as 10%. A low indeterminate rate means more providers and patients may confidently use test results to help make clinical decisions in real-world settings."

The study evaluated two blood-based tests developed by Quest Diagnostics. One of the tests produces a likelihood score based on results of circulating blood levels of the biomarkers amyloid beta (AB) 42/40, phosphorylated tau (p-tau) 217 and ApoE4 proteotype (reflecting inherited high-risk APOE4 alleles). Quest plans to launch a version of this test in the first quarter of 2026. The study also evaluated a test that includes AB 42/40 and p-tau217 but not ApoE4. The company launched a version of this test (called AD-Detect™ ABeta  42/40 and p-tau217 Evaluation panel) in April 2025.

Both tests were evaluated at 91% sensitivity and 91% specificity to meet acceptable performance of confirmatory blood biomarker tests in an intended-use population of 215 patients with mild cognitive impairment (MCI) or Alzheimer's disease in which 46% were amyloid PET-positive. Both the Alzheimer's Association (AA) and the Global CEO Initiative on Alzheimer's Disease (CEOi) recommend that a blood-based test for confirmatory use without follow-up testing have a sensitivity and specificity of approximately 90%, comparable to CSF testing. (The AA recommendations pertain to patients with objective cognitive impairment presenting to specialized care settings, while the CEOi recommendations pertain to patients for whom amyloid positivity is highly likely to be greater than 50%.)

With cutoffs of 91% sensitivity and 91% specificity, the test combining AB 42/40, p-tau217 and ApoE4 blood tests had a positive predictive value (PPV, or evidence of a true positive result) of 88% and a negative predictive value of 91% (NPV, or evidence of a true negative result) in the intended-use population. A panel that did not include ApoE4 had slightly lower PPV (87%) and no change in NPV (91%). Predictive values can vary based on prevalence of disease in a population and may therefore provide more useful insight than sensitivity and specificity alone.

In addition, the indeterminate rate was 10% for the test with all three biomarkers and 15% for the test without ApoE4. The CEOi recommends that blood-based tests for confirmatory use classify no more than 15%-20% of individuals with an indeterminate result.

The findings were first presented during an oral presentation at the American Academy of Neurology (AAN)'s Annual Meeting in San Diego in April 2025.

Quest performs AB 42/40 and ApoE4 proteotype using proprietary tandem mass spectrometry techniques and p-tau271 using a third-party immunoassay. Quest AD-Detect tests are intended for use by physicians to evaluate patients with symptoms of cognitive impairment or Alzheimer's disease.

Nearly 7 million Americans have been diagnosed with Alzheimer's disease, the most prevalent form of dementia, a number projected to reach 14 million by 2060. Approximately 12-18% of adults over the age of sixty are living with mild cognitive impairment, a potential sign of AD. Ninety-four percent of physicians say blood tests would be more cost effective for the healthcare system compared to more invasive methods of detection (e.g., CSF lumbar puncture, PET imaging), according to a report from Quest.

Quest is committed to developing innovative advanced diagnostics to aid in evaluating Alzheimer's disease and other brain diseases. For more information, visit www.QuestForTheCure.com.

About Quest Diagnostics
Quest Diagnostics works across the healthcare ecosystem to create a healthier world, one life at a time. We provide diagnostic insights from the results of our laboratory testing to empower people, physicians and organizations to take action to improve health outcomes. Derived from one of the world's largest databases of de-identifiable clinical lab results, Quest's diagnostic insights reveal new avenues to identify and treat disease, inspire healthy behaviors and improve healthcare management. Quest Diagnostics annually serves one in three adult Americans and half the physicians and hospitals in the United States, and our nearly 55,000 employees understand that, in the right hands and with the right context, our diagnostic insights can inspire actions that transform lives and create a healthier world. www.QuestDiagnostics.com.

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SOURCE Quest Diagnostics

FAQ

What accuracy did Quest AD-Detect tests achieve in the Oct 27, 2025 study for DGX?

Both AD-Detect panels reached 91% sensitivity and 91% specificity in the intended-use cohort.

What are the PPV and NPV for Quest's three-biomarker AD-Detect test (DGX) reported Oct 27, 2025?

The three-biomarker panel showed PPV 88% and NPV 91% in the study cohort with 46% amyloid prevalence.

When did Quest (DGX) launch the AD-Detect two-biomarker panel and when is the three-biomarker version planned?

The two-biomarker AD-Detect panel launched in April 2025; a three-biomarker version is planned for Q1 2026.

How often did Quest AD-Detect produce indeterminate results in the Oct 27, 2025 study?

The three-biomarker test had a 10% indeterminate rate; the two-biomarker test had a 15% indeterminate rate.

Do Quest AD-Detect results aim to replace PET or CSF testing for Alzheimer's (DGX)?

The study suggests the tests meet guideline thresholds to support confirmatory use without routine PET or CSF follow-up in intended-use symptomatic patients.

What biomarkers are included in Quest AD-Detect tests evaluated in the Oct 27, 2025 study?

The evaluated panels used AB42/40 and p-tau217, with the three-biomarker panel adding an ApoE4 proteotype marker.