A simple blood test designed to help detect early signs of Alzheimer’s disease has passed a key practical test: its measurements remain reliable even when blood samples are handled and stored in a variety of everyday conditions. The finding comes from a prospective observational study published in Alzheimer’s Research & Therapy, which evaluated the Elecsys Phospho-Tau (181P) plasma immunoassay developed by Roche Diagnostics.
The assay measures plasma tau phosphorylated at threonine 181, known as pTau181, a blood-based biomarker that correlates with the burden of amyloid-beta pathology in Alzheimer’s disease. The immunoassay is intended for use as an aid in the early detection of amyloid-beta pathology in adults aged 55 years and older who present with complaints of cognitive decline. It is Conformité Européenne-marked and has been approved for clinical use by the US FDA.
The study recruited individuals presenting at LMU Hospital whose symptom severity ranged from subjective cognitive decline to moderate Alzheimer’s disease dementia. Whole blood samples were collected in three different tube types used for plasma preparation: lithium heparin, K2-EDTA, and K3-EDTA. The samples were transported under cooled conditions, never frozen, to the measurement site and processed within six hours of collection.
Plasma samples were then stored at different temperatures for varying durations, and the researchers assessed the impact on pTau181 recoveries compared with pre-defined acceptance criteria. This design allowed the team to determine how long the biomarker remains dependable under realistic pre-analytical scenarios, from a warm bench to long-term freezer storage.
The first round of testing revealed an important practical lesson. In an initial cohort of 14 participants, out-of-specification results that failed the acceptance criteria were traced back to contamination of the plasma with buffy coat and erythrocytes, the cellular components of blood. Rather than reflecting true instability of the biomarker, these failures stemmed from how the plasma was transferred after centrifugation.
In response, the pre-analytical procedures were modified to prevent such contamination during post-centrifugation plasma transfer. When the protocol was repeated in a separate cohort of 10 participants, no instabilities were observed and all acceptance criteria were met. The change in sample handling, rather than any property of the assay itself, resolved the discrepancies seen in the first cohort.
After incorporating safety margins, the researchers determined analyte stability for all sample types to be two days at 25 degrees Celsius, seven days at 4 degrees Celsius, 12 weeks at minus 20 degrees Celsius, and 16 weeks at minus 80 degrees Celsius. Stability was also observed after one freeze/thaw cycle, a common occurrence when samples are transported between laboratories or stored before analysis.
The authors conclude that measurements with the pT181p immunoassay were stable and robust with respect to different sample handling procedures and storage conditions. According to the study, these findings support implementation of the assay into routine, non-specialist healthcare settings to facilitate practical blood-based testing to rule out Alzheimer’s disease-related amyloid-beta pathology.
As a prospective observational stability study in a small number of participants from a single hospital, its scope is deliberately narrow: it establishes how the biomarker withstands pre-analytical handling in an intended-use population, rather than evaluating diagnostic accuracy itself. Even so, the results address a necessary precondition for bringing blood-based Alzheimer’s testing out of specialist centres and into everyday clinical practice.
Subject of Research: Stability of plasma pTau181 measured by the Elecsys Phospho-Tau (181P) immunoassay for early detection of Alzheimer's disease amyloid pathology
Article Title: A prospective observational study measuring the stability of plasma pTau181 using the Elecsys Phospho-Tau (181P) plasma immunoassay for early detection of Alzheimer’s disease
Article References: Kurz, C., Leonhardt, S., Hufnagel, A., Wizemann, S., Deutelmoser, H., Menzel, P., & Perneczky, R. (2026). A prospective observational study measuring the stability of plasma pTau181 using the Elecsys Phospho-Tau (181P) plasma immunoassay for early detection of Alzheimer’s disease. Alzheimer's Research & Therapy. https://doi.org/10.1186/s13195-026-02238-7
Image Credits: AI Generated
DOI: 10.1186/s13195-026-02238-7
Keywords: Alzheimer's disease, pTau181, blood biomarker, Elecsys immunoassay, plasma stability, amyloid-beta pathology, pre-analytical conditions, sample storage, early detection, Roche Diagnostics, cognitive decline, LMU Hospital
News Source: Diana Fleming. (October 28, 2026). Blood Test for Early Alzheimer’s Detection Stays Stable Across Storage Conditions. Scienmag.
