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

BackgroundPlasma phosphorylated tau₂₁₇ (p-tau₂₁₇) 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.ObjectiveTo examine the cross-sectional and longitudinal associations between plasma p-tau₂₁₇ concentration and cerebrospinal fluid (CSF) AD biomarkers. Further, to investigate the performance of p-tau₂₁₇ as a predictor of amyloid status in a cohort of very old men.MethodsCSF AD biomarkers were analyzed in thirty-five 89-year-old men. Amyloid-β (Aβ) positivity was defined according to CSF Aβ₄₂ level. Plasma p-tau₂₁₇ 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.ResultsPlasma p-tau₂₁₇ strongly correlated with CSF Aβ₄₂ concentration in Aβ-positive (n = 16, Spearman <i>ρ</i>: rho = -0.63, <i>p</i> = 0.009) but not in Aβ-negative (n = 19, rho = 0.111, <i>p</i> = 0.652) men and predicted Aβ status (area under the curve, AUC 0.91). Plasma p-tau₂₁₇ increased over ten years in the Aβ-positive group, while it remained unchanged in the negative group (p = 0.018).ConclusionsOur findings indicate that plasma p-tau₂₁₇ is a predictor of brain Aβ deposition also in very old individuals.