Blood Test Accurately Detects Alzheimer's Amyloid Pathology in Symptomatic Adults: Latest 2026 Study Findings

Blood-based biomarker test combining plasma phosphorylated tau 217 (p-tau217) and amyloid beta 1-42 (Aβ1-42) can accurately identify amyloid pathology in adults with cognitive symptoms, potentially offering a less invasive alternative to cerebrospinal fluid (CSF) testing and amyloid positron emission tomography (PET) imaging, according to findings from a recent study.

The study was published in the June 2026 issue of Alzheimer's & Dementia, the Journal of the Alzheimer's Association.

Alzheimer's Disease-Evolving Diagnostic Modalities

Alzheimer's disease is the most common cause of dementia and is characterized by the accumulation of amyloid beta plaques and neurofibrillary tau tangles in the brain. Currently, confirmation of amyloid pathology relies primarily on CSF biomarker analysis or amyloid PET imaging. While these methods are considered accurate, they are invasive, expensive, and often unavailable outside specialized centers. The emergence of disease-modifying therapies has further increased the need for accessible diagnostic tools capable of identifying patients eligible for treatment.

Blood-based biomarkers (BBMs) have emerged as promising alternatives for Alzheimer's disease diagnosis. Several plasma biomarkers, including p-tau217, p-tau181, Aβ42/40, and neurofilament light chain, are currently being investigated for their ability to detect amyloid and tau pathology, facilitate early diagnosis, and identify patients who may benefit from confirmatory CSF or PET testing.

Study Overview

To validate the diagnostic performance of the plasma p-tau217/Aβ1-42 ratio, researchers conducted a multicentre validation study using frozen plasma samples from five independent clinical cohorts: POLARIS-AD, BioFINDER-2, Bio-Hermes-001, the Wisconsin Alzheimer's Disease Research Center (WADRC), and the Wisconsin Registry for Alzheimer's Prevention (WRAP).

The study included 499 adults aged 52-93 years (mean age 72 years), of whom 51.9% were women. Based on harmonized clinical classification, 290 participants had Alzheimer's disease, 154 had mild cognitive impairment (MCI), 49 had subjective cognitive decline, and six had other forms of dementia. Amyloid pathology was established using either CSF biomarker ratios or amyloid PET imaging, which served as the reference standards.

Instead of deriving new diagnostic thresholds, previously established plasma p-tau217/Aβ1-42 ratio cut-offs: ≤0.00370 was considered negative, 0.00371-0.00737 indeterminate, and ≥0.00738 positive. A negative result indicated a low likelihood of amyloid pathology, whereas a positive result indicated a high likelihood of underlying Alzheimer's pathology.

Some of the key results of the study include:

Amyloid pathology in the reference cohorts

• Among the 347 participants who underwent CSF biomarker testing, 189 (54.5%) were amyloid positive, and 158 (45.5%) were amyloid negative. Of the 152 participants assessed using amyloid PET imaging, 66 (43.4%) were amyloid positive while 86 (56.6%) were amyloid negative. Overall, 255 of the 499 participants (51.1%) were confirmed to have amyloid pathology.

Plasma ratio showed strong agreement with CSF and PET findings

• Using the predefined plasma p-tau217/Aβ1-42 ratio thresholds, the blood test classified 219 patients (43.9%) as positive, 182 (36.5%) as negative, and 98 (19.6%) as indeterminate. Notably, the indeterminate rate remained below the 20% benchmark recommended by the Alzheimer's Association for blood-based biomarkers.

Diagnostic Accuracy

• The assay demonstrated strong agreement with the reference standards. Among the 219 plasma-positive patients, 201 were true positives, and only 18 were false positives, resulting in a positive predictive value (PPV) of 91.8% (95% CI, 87.8%-94.6%).
• Similarly, among the 182 plasma-negative patients, 177 were true negatives, with only five false-negative results, yielding a negative predictive value (NPV) of 97.3% (95% CI, 93.9%-98.8%).
• After excluding indeterminate results, the plasma biomarker ratio achieved an overall sensitivity of 97.6% (95% CI, 94.4%-99.0%) and specificity of 90.8% (95% CI, 85.9%-94.1%), indicating that the assay correctly identified nearly 98% of patients with amyloid pathology while accurately excluding disease in approximately 91% of patients without amyloid pathology.

These findings indicate that the blood test correctly identified nearly 98% of patients with amyloid pathology while accurately ruling out disease in approximately 91% of patients without amyloid pathology.

Figure 1: Key Study Findings

Performance in patients with cognitive impairment

• The test also maintained excellent performance among the 444 participants diagnosed with Alzheimer's disease or mild cognitive impairment, achieving a sensitivity of 97.4%[95% CI:94.1% to 98.9%], specificity of 90.0% [95% CI:84.6% to 93.7%], PPV of 91.7%, and NPV of 96.8%, supporting its potential utility in patients undergoing routine clinical evaluation for cognitive impairment.

Consistent results across different patient groups

• The diagnostic performance remained consistent across multiple demographic and clinical subgroups, including age, sex, race and ethnicity, body mass index, APOE ε4 carrier status, clinical diagnosis, study cohort, and reference method (CSF or PET), suggesting that these variables did not significantly influence test accuracy.

Comparison with plasma p-tau217 alone

• The combined plasma p-tau217/Aβ1-42 ratio was also compared with plasma p-tau217 alone. Although p-tau217 individually showed good diagnostic performance, combining it with Aβ1-42 significantly improved overall accuracy. The combined biomarker achieved a significantly higher area under the receiver operating characteristic (ROC) curve (AUC 0.9457 vs. 0.9305; p=0.001), produced fewer indeterminate results, and demonstrated better discrimination between amyloid-positive and amyloid-negative individuals.

Potential Clinical Implications of Blood-Based Biomarkers in Alzheimer's Disease

The study suggests that blood-based biomarker testing using the plasma p-tau217/Aβ1-42 ratio allows a step-wise approach to simplify the diagnostic evaluation of patients with cognitive impairment, facilitating optimal utilisation of healthcare resources through the early use of blood-based biomarkers in Alzheimer's disease.

• The study supports the growing role of blood-based biomarkers in the evaluation of Alzheimer's disease. The plasma p-tau217/Aβ1-42 ratio demonstrated high diagnostic accuracy and may complement existing diagnostic pathways by helping identify patients who are more likely to benefit from confirmatory CSF or PET testing.
• In addition, the blood-based biomarker evaluated in this study has received US FDA clearance, supporting its use as an aid in identifying amyloid pathology in appropriate clinical settings.

Abbreviations: CSF: Cerebrospinal Fluid, PET: Positron Emission Tomography, BBMs: Blood-Based Biomarkers, p-tau217: Plasma Phosphorylated Tau 217, p-tau181: Plasma Phosphorylated Tau 181, Aβ1-42: Amyloid Beta 1-42, Aβ42/40: Amyloid Beta 42/40 Ratio, MCI: Mild Cognitive Impairment, AD: Alzheimer's Disease, PPV: Positive Predictive Value, NPV: Negative Predictive Value, CI: Confidence Interval, BMI: Body Mass Index, APOE ε4: Apolipoprotein E Epsilon 4, ROC: Receiver Operating Characteristic, AUC: Area Under the Receiver Operating Characteristic Curve, FDA: United States Food and Drug Administration, WADRC: Wisconsin Alzheimer's Disease Research Center, WRAP: Wisconsin Registry for Alzheimer's Prevention.

Reference:

1) Moghekar AR, Rock JA, Mohs RC, et al.Multicenter validation of plasma p-tau217/ amyloid beta 1-42 ratio in symptomatic Alzheimer’s disease. Alzheimer’s Dement. 2026;22:e71644. https://doi.org/10.1002/alz.71644

CMAT-42456 | 24-08-2026

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