Objective: The objective of this study was to examine clinicians' patient selection and result interpretation of a clinically validated mass spectrometry test measuring amyloid beta and ApoE blood biomarkers combined with patient age (PrecivityAD® blood test) in symptomatic patients evaluated for Alzheimer's disease (AD) or other causes of cognitive decline.Methods: The Quality Improvement and Clinical Utility PrecivityAD Clinician Survey (QUIP I, ClinicalTrials.gov Identifier: NCT05477056) was a prospective, single‐arm cohort study among 366 patients evaluated by neurologists and other cognitive specialists. Participants underwent blood biomarker testing and received an amyloid probability score (APS), indicating the likelihood of a positive result on an amyloid positron emission tomography (PET) scan. The primary study outcomes were appropriateness of patient selection as well as result interpretation associated with PrecivityAD blood testing.Results: A 95% (347/366) concordance rate was noted between clinicians' patient selection and the test's intended use criteria. In the final analysis including these 347 patients (median age 75 years, 56% women), prespecified test result categories incorporated 133 (38%) low APS, 162 (47%) high APS, and 52 (15%) intermediate APS patients. Clinicians' pretest and posttest AD diagnosis probability changed from 58% to 23% in low APS patients and 71% to 89% in high APS patients (p < 0.0001). Anti‐AD drug therapy decreased by 46% in low APS patients (p < 0.0001) and increased by 57% in high APS patients (p < 0.0001).Interpretation: These findings demonstrate the clinical utility of the PrecivityAD blood test in clinical care and may have added relevance as new AD therapies are introduced.

Alzheimer’s disease (AD) is a progressive irreversible neurodegenerative disorder that represents a major global public health concern. Traditionally, AD is diagnosed using cerebrospinal fluid biomarker analysis or brain imaging modalities. Recently, less burdensome, more widely available blood biomarker (BBM) assays for amyloid-beta (Aβ42/40) and phosphorylated-tau concentrations have been found to accurately identify the presence/absence of brain amyloid plaques and tau tangles and have helped to streamline AD diagnosis. However, few BBMs have been rigorously analytically validated. Herein, we report the analytical validation of a novel liquid chromatography–tandem mass spectrometry (LC-MS/MS) multiplex method for quantifying plasma phosphorylated-tau217 (p-tau217) and non-phosphorylated-tau217 (np-tau217) peptide concentrations. We combined the p-tau217/np-tau217 concentrations ratio (%p-tau217) and the previously validated LC-MS/MS multiplex assay for plasma Aβ42/40 into a new multianalyte assay with algorithmic analysis (MAAA; PrecivityAD2™ test) that identifies brain amyloid status based on brain amyloid positron emission tomography. We found (a) the %p-tau217 assay is precise, accurate, sensitive, and linear over a wide analytical measurement range, and free from carryover and interference; (b) the pre-analytical specimen collection, processing, storage, and shipping conditions that maintain plasma tau peptide stability; and (c) using the measured analytical imprecision for plasma Aβ42/40 and p-tau217/np-tau217 levels in a worst-case scenario model, the PrecivityAD2 test algorithm for amyloid pathology classification changed for only 3.5% of participants from brain amyloid positive to negative, or from negative to positive. The plasma sample preparation and LC-MS/MS methods underlying the PrecivityAD2 test are suitable for use in the clinical laboratory and valid for the test’s intended purpose: to aid in the diagnostic evaluation of individuals aged 55 and older with signs or symptoms of mild cognitive impairment or dementia.

Alzheimer’s disease (AD) is a progressive irreversible neurodegenerative disorder that represents a major global public health concern. Traditionally, AD is diagnosed using cerebrospinal fluid biomarker analysis or brain imaging modalities. Recently, less burdensome, more widely available blood biomarker (BBM) assays for amyloid-beta (Aβ42/40) and phosphorylated-tau concentrations have been found to accurately identify the presence/absence of brain amyloid plaques and tau tangles and have helped to streamline AD diagnosis. However, few BBMs have been rigorously analytically validated. Herein, we report the analytical validation of a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying plasma phosphorylated-tau217 (p-tau217) and non-phosphorylated-tau217 (np-tau217) peptide concentrations. We combined the p-tau217/np-tau217 concentrations ratio (%p-tau217) and the previously validated LC-MS/MS assay for plasma Ab42/40 into a new multiple analyte blood test and algorithm (PrecivityAD2™) that identifies brain amyloid status based on brain amyloid positron emission tomography. We found: (a) the %p-tau217 assay is precise, accurate, sensitive, linear over a wide analytical measurement range, and free from carryover and interference; (b) the pre-analytical specimen collection, processing, storage and shipping conditions that maintain plasma tau peptide stability; and (c) using the measured analytical imprecision for plasma Aβ42/40 and p-tau217/np-tau217 levels in a worst-case scenario model, the PrecivityAD2 test algorithm for amyloid pathology classification changed for only 3.5% of participants from brain amyloid positive to negative, or negative to positive. The plasma sample preparation and LC-MS/MS methods underlying the PrecivityAD2 test are suitable for use in the clinical laboratory and valid for the test’s intended purpose: to aid in the diagnostic evaluation of individuals aged 55 and older with signs or symptoms of mild cognitive impairment or dementia.

The diagnostic performance of the Amyloid Probability Score 2 (APS2; the algorithmic result of the PrecivityAD2™ blood test) was originally trained and validated in two cohorts of cognitively impaired (CI) individuals and is in clinical use. Here, we further test the repeatability and reliability of the prespecified APS2 algorithm and cut point in an independent cohort. APS2 diagnostic performance was determined using amyloid positron emission tomography (PET) as the reference standard. Concordance with amyloid PET was high (AUC–ROC 0.95 (95% CI): 0.93–0.98); 54% of participants had a positive APS2. The previously validated APS2 cut point yielded an overall accuracy of 91% (95% CI: 86–94%), sensitivity 90% (95% CI: 83–94%) and specificity 92% (95% CI: 84–96%). Our findings demonstrate that the prespecified APS2 algorithm and cut point are repeatable, reliable, robust, accurate, and generalizable for identifying brain beta-amyloid pathology in patients with cognitive impairment and being evaluated in a clinical care setting.

Objective: The diagnostic performance of the Amyloid Probability Score 2 (APS2) - the algorithmic result of the PrecivityAD2™ blood test - was originally trained and validated in two cohorts of cognitively impaired (CI) individuals. Using an independent cohort to evaluate blood test reliability, we conducted an external diagnostic accuracy assessment of the validated APS2 cut point as it is currently applied in clinical practice. Methods: Plasma biomarker ratios Aβ42/40 and p-tau217/np-tau217 (expressed as %p-tau217) were quantified and incorporated into the APS2 algorithm in samples obtained from 192 Alzheimer’s Disease Neuroimaging Initiative participants with CI (70% mild cognitive impairment / 30% dementia). APS2 diagnostic performance was determined using amyloid positron emission tomography (PET) as the reference standard. Plasma biomarkers were quantified in a CLIA-certified, CAP-accredited laboratory (C2N Diagnostics, St. Louis, MO) using liquid chromatography-tandem mass spectrometry. Results: APS2 values were significantly higher in the 56% of CI participants with a positive amyloid PET scan. Concordance with amyloid PET was high (AUC-ROC 0.95 (95%CI): 0.93– 0.98); 54% of participants had a positive APS2. The previously validated APS2 cut point yielded an overall accuracy of 91% (95%CI: 86-94%), sensitivity 90% (95%CI: 83-94%) and specificity 92% (95%CI: 84-96%). Interpretation: The PrecivityAD2 blood test’s APS2 identified brain amyloid pathology with accuracy, sensitivity, and specificity ≥ 90% in this intended use population. This external validation reaffirms the diagnostic robustness of this blood biomarker test and supports its use as a confirmatory test, consistent with published expert recommendations, for assessment of presence or absence of brain amyloid pathology in symptomatic patients.