Accuracy of FDA-Cleared Alzheimer’s Blood Test Evaluated in a Real-World Cohort

A study presented at the 18th annual Clinical Trials on Alzheimer’s Disease (CTAD) conference evaluated the Food and Drug Administration (FDA)-cleared and clinically available Lumipulse G pTau 217/ β-Amyloid 1-42 Plasma Ratio (Fujirebio Diagnostics, Malvern, PA) test for detecting amyloid pathology. Results from the study demonstrated that when the FDA-cleared ratio cutpoints were used, the test’s accuracy varied substantially between a real-world memory clinic cohort and a research cohort enriched for Alzheimer disease (AD) risk. The findings suggest that, although the FDA-cleared cutpoints performed well in research settings, additional validation may be needed for routine clinical populations.

The study assessed the efficacy of Lumipulse G pTau 217/ β-Amyloid 1-42 Plasma Ratio in 2 independent cohorts. The first was a real-world clinical cohort comprising 252 individuals who had participated in a prospective study at a tertiary care subspecialty clinic. The second, risk-enriched research cohort included 101 individuals from the Wisconsin Alzheimer’s Disease Research Center and the Wisconsin Registry for Alzheimer’s Prevention. Plasma phosphorylated tau217 (p-tau217) and beta amyloid 1-42 (β-amyloid 1-42) were measured using the Lumipulse G pTau 217/ β-Amyloid 1-42 Plasma Ratio assay, with results stratified as positive, intermediate, or negative using the FDA-cleared Lumipulse pTau217/Aβ42 ratio cutpoints. The results were also stratified based on previously established, in-house ratio cutpoints, as well p-tau217 concentration thresholds alone. Both cohorts included individuals with cognitive impairment undergoing amyloid biomarker evaluation.

In the research cohort:

• FDA-cleared ratio cutpoints yielded 99% sensitivity and 85% specificity, with 95% diagnostic accuracy.
• In-house ratio cutpoints yielded 88% sensitivity and 96% specificity, with 91% diagnostic accuracy.
• Plasma p-tau217 thresholds alone yielded 89% sensitivity and 96% specificity, with 91% diagnostic accuracy.

In the real-world, clinical cohort:

• FDA-cleared ratio cutpoints yielded 100% sensitivity and 23% specificity, with 77% diagnostic accuracy.
• In-house ratio cutpoints yielded 100% sensitivity, 79% specificity, and 94% accuracy.
• Plasma p-tau217 thresholds alone yielded 98% sensitivity, 84% specificity, and 94% accuracy.

Source: Algeciras-Schimnich A, Ashrafzadeh Kian S, Rea Reyes R, et al. Diagnostic performance of the FDA-cleared Lumipulse G pTau217/Aβ42 plasma ratio thresholds for detection of amyloid pathology. Presented at: 18th annual Clinical Trials on Alzheimer’s Disease Conference; December 1-4, 2025; San Diego, California.