Plasma p-tau ₂₁₇ correlates strongly with cerebrospinal fluid Aβ ₄₂ and increases over a ten-year period in amyloid-positive, non-demented very old men

Background Plasma phosphorylated tau 217 (p-tau 217 ) is a robust biomarker of Alzheimer's disease (AD) pathology. However, its full potential as a dynamic marker has still not been verified in very old persons, i.e., those with the highest incidence of AD. Objective To examine the cross-sectional and longitudinal associations between plasma p-tau 217 concentration and cerebrospinal fluid (CSF) AD biomarkers. Further, to investigate the performance of p-tau 217 as a predictor of amyloid status in a cohort of very old men. Methods CSF AD biomarkers were analyzed in thirty-five 89-year-old men. Amyloid-β (Aβ) positivity was defined according to CSF Aβ 42 level. Plasma p-tau 217 concentration was measured at the mean age of 82, 87, and 91. Incident dementia diagnoses in survivors were identified through medical records up to the age of 102. Results Plasma p-tau 217 strongly correlated with CSF Aβ 42 concentration in Aβ-positive (n = 16, Spearman ρ : rho = −0.63, p = 0.009) but not in Aβ-negative (n = 19, rho = 0.111, p = 0.652) men and predicted Aβ status (area under the curve, AUC 0.91). Plasma p-tau 217 increased over ten years in the Aβ-positive group, while it remained unchanged in the negative group (p = 0.018). Conclusions Our findings indicate that plasma p-tau 217 is a predictor of brain Aβ deposition also in very old individuals.