Résumé
BACKGROUND Alzheimer disease (AD), the leading cause of dementia, has increased interest in the development of blood-based biomarkers for early diagnosis and monitoring. The plasma amyloid beta (A beta)42/A beta 40 ratio and phosphorylated tau (p-tau) isoforms closely align with cerebrospinal fluid and positron emission tomography markers. The recent approval of the plasma p-tau217/A beta 42 ratio marks a key step toward non-invasive diagnostics. However, known A beta 42's preanalytical and analytical challenges raise concerns about the reliability of this ratio in routine clinical practice. METHODS Using the ALZAN prospective cohort of cognitively impaired individuals, we examined how delays between blood collection and laboratory processing affected the performance of plasma biomarkers in detecting. RESULTS The preanalytical delay has a significant impact for A beta 40 and A beta 42. However, the performance of p-tau217 and p-tau217/A beta 42 ratio were similar, thereby supporting the use of the ratio as a robust and efficient marker for AD diagnosis. DISCUSSION Our findings reinforce the high diagnostic accuracy of the p-tau217/A beta 42 ratio in AD, regardless of preanalytical delays.