Sequential Plasma p-Tau217 Workflow Reduces Diagnostic Uncertainty in Memory Clinics

A sequential blood-testing strategy that utilizes the plasma p-tau217/Aβ42 ratio as a secondary reflexive test for patients with intermediate standalone p-tau217 results significantly reduces diagnostic uncertainty in real-world memory clinic settings, according to a retrospective investigation published in Alzheimer’s Research & Therapy. Blood-based biomarkers have increasingly entered specialist diagnostic pathways, with standalone p-tau217 receiving CE-IVDR marking in Europe and the p-tau217/Aβ42 ratio gaining clearance from the Food and Drug Administration in the United States for assessing Alzheimer’s disease amyloid pathology. However, determining how to optimally incorporate these tools into clinical pathways that account for diagnostic uncertainty, particularly when evaluating patients whose biomarker concentrations fall near established clinical decision thresholds, has presented an ongoing practical challenge.

To investigate practical diagnostic strategies, a research team led by Giordano Cecchetti, Federica Agosta, Massimo Filippi, and colleagues retrospectively examined clinical records from 562 consecutive patients who underwent clinical evaluation at a specialized memory clinic between October 2023 and April 2026. The researchers established Core1 amyloid status for all participants using cerebrospinal fluid biomarkers, amyloid positron emission tomography, or both diagnostic modalities, aligning with the 2024 Alzheimer’s Association Revised Criteria. Within this evaluated real-world patient population, the measured prevalence of Core1-positive amyloid pathology was 71.2 percent, accounting for 400 individuals.

All plasma biomarker concentrations were quantified using the automated Lumipulse G600II laboratory assay platform. The researchers systematically modeled and evaluated three distinct two-threshold diagnostic pathways: a standalone p-tau217 pathway, a universal upfront pathway that measured the p-tau217/Aβ42 ratio across all patients, and a sequential testing model where the p-tau217/Aβ42 ratio was reserved strictly for individuals whose initial p-tau217 test yielded an intermediate finding. In designing these diagnostic thresholds, the investigators deliberately selected rule-out and rule-in cutoff values calibrated to maintain at least 95 percent sensitivity and at least 95 percent specificity, respectively.

When evaluated individually across the patient cohort, plasma p-tau217 delivered an area under the receiver operating characteristic curve of 0.935, with a 95 percent confidence interval extending from 0.908 to 0.962. This standalone assay substantially outperformed several comparator plasma biomarkers, including p-tau181, which reached an area under the curve of 0.826, the Aβ42/Aβ40 ratio at 0.797, glial fibrillary acidic protein at 0.789, and neurofilament light chain at 0.566, with every comparative difference reaching statistical significance at p < 0.001. Applying the predefined two-threshold cutoff approach to standalone p-tau217 left 17.8 percent of the patient cohort in an intermediate diagnostic zone, while yielding 94.1 percent accuracy within the definitive decision zones.

Implementing the p-tau217/Aβ42 ratio as a universal upfront test produced a statistically higher overall global discrimination than standalone p-tau217 alone, achieving an area under the curve of 0.946 with a p-value of 0.011. Despite this higher global metric, universal upfront testing offered only a negligible clinical improvement in diagnostic clarity, reducing the intermediate zone from 17.8 percent down to 17.1 percent. In contrast, implementing the p-tau217-first sequential workflow reduced the intermediate zone to 12.3 percent, successfully resolving diagnostic ambiguity for a substantially larger fraction of the memory clinic cohort.

The clinical impact of this intermediate-zone reduction is substantial, as the p-tau217-first sequential model spared an estimated 56 confirmatory cerebrospinal fluid analyses or amyloid positron emission tomography scans per 1,000 evaluated patients. In terms of overall classification metrics, this sequential approach demonstrated a sensitivity of 0.937, a specificity of 0.935, a positive predictive value of 0.973, and a negative predictive value of 0.855, maintaining robust diagnostic precision while decreasing reliance on invasive or cost-intensive confirmatory procedures.

The investigators also conducted sensitivity analyses and temporal validation to evaluate the stability of these clinical pathways. A reverse sequential model, in which the ratio was tested first and standalone p-tau217 was applied secondarily, yielded classification performance comparable to the p-tau217-first approach but required running the more complex ratio upfront across the entire patient cohort. Furthermore, internal temporal validation confirmed the transportability of the sequential testing strategy, demonstrating a validation area under the curve of 0.941 with a delta AUC of plus 0.018 (p = 0.54), even across a temporal cohort shift that exhibited a 15-percentage-point difference in baseline Core1-positive prevalence.

Based on these findings, the authors concluded that the slightly higher global discrimination observed with upfront p-tau217/Aβ42 testing does not deliver a meaningful reduction in clinical indeterminacy when deployed as a universal first-line replacement for standalone p-tau217 in real-world memory clinic workflows. Instead, the clinical utility of the ratio is maximized when positioned as a targeted second-step assay specifically for patients falling within the p-tau217 intermediate zone, providing practical support for uncertainty-aware testing algorithms that effectively prioritize confirmatory cerebrospinal fluid analysis or amyloid positron emission tomography neuroimaging.

Subject of Research: Sequential plasma p-tau217 diagnostic workflows for Alzheimer's disease amyloid pathology in memory clinics

Article Title: Reducing Alzheimer’s diagnostic uncertainty with a sequential plasma p-tau217 workflow in real-world memory clinic practice

Article References: Cecchetti, G., Agosta, F., Rugarli, G., Coraglia, F., Bertù, S., Breschi, A., Ghirelli, A., Spinelli, E. G., Pisano, S., & Filippi, M. (2026). Reducing Alzheimer’s diagnostic uncertainty with a sequential plasma p-tau217 workflow in real-world memory clinic practice. Alzheimer's Research & Therapy. https://doi.org/10.1186/s13195-026-02218-x

Image Credits: AI Generated

DOI: 10.1186/s13195-026-02218-x

Keywords: Alzheimer's disease, plasma biomarkers, p-tau217, memory clinic, diagnostic accuracy, amyloid pathology, lumipulse, Reducing, Alzheimer, diagnostic, uncertainty, sequential