Current practices and harmonization challenges in Alzheimer’s disease biomarkers: an EFLM Committee: Harmonization Survey

Abstract Objectives Fluid biomarkers are central to the biological definition and diagnosis of Alzheimer’s disease (AD). Despite international recommendations, substantial variability persists in laboratory practices. This survey, promoted by the Committee: Harmonisation (C:H) of the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM), aimed to assess real-world laboratory practices for AD biomarker testing. Methods An online survey was distributed to EFLM members. The questionnaire addressed pre-analytical, analytical, and post-analytical practices for cerebrospinal fluid (CSF) and blood-based AD biomarkers. Descriptive statistics were applied. Results A total of 316 responses from more than 35 countries were collected. CSF remained the primary matrix for AD diagnostics, although blood-based biomarkers were increasingly implemented. Marked heterogeneity was observed across all phases of testing, including sample handling, assay platforms, biomarker panels, and decisional cut-offs. Cut-off values for core biomarkers varied widely, as well as harmonization of reporting unit and the adoption of SI units preventing a shared approach to interpreting the results. Conclusions Despite growing clinical adoption, AD biomarker testing remains highly heterogeneous. Coordinated international harmonization of pre-analytical procedures, analytical methods, and post-analytical interpretation, particularly for blood-based biomarkers, is urgently required to ensure reliable and comparable results.