Clinical value of plasma ALZpath pTau217 immunoassay for assessing mild cognitive impairment

Abstract

Objectives We sought to compare two of the most promising plasma biomarkers for Alzheimer disease: pTau181 and pTau217. Methods pTau181 and pTau217 were quantified using SIMOA Quanterix and ALZpath assays in the well characterized prospective multicentre BALTAZAR cohort of mild cognitive impairment (MCI) participants. Results Among MCI participants, 55% were Aβ+ and 29% developed dementia due to AD. pTau181 and pTau217 were higher in the Aβ+ population with fold-change of 1.5 and 2.7 respectively. Concentration were also higher in MCI that converted to AD versus with hazard ratio of 1.38 (1.26-1.51) for pTau181 compared to 8.22 (5.45-12.39) for pTau217. The AUC for predicting Aβ+ was 0.783 (95%CI: 0.721-0.836; cut-point 2.75 pg/mL) for pTau181 and 0.914 (95%CI: 0.868-0.948; cut-point 0.44 pg/mL) for pTau217. The predictive power of pTau217 was not improved by adding age, sex, and APOEε4 status in a logistic model. The confounding factors of age, APOEε4 or renal dysfunction were associated with both pTau levels, but pTau217 clinical performance was only marginally modified by these comorbidities. Using a two cut-point approach, a 95% positive predictive value for Aβ+ corresponded to pTau217 > 0.8 ng/mL and a 95% negative predictive value at <0.23 ng/mL. At these two cut-points, the percentages of MCI conversion were 56.8% and 9.7% respectively, while the annual rates of decline in MMSE were -2.32 versus -0.65. Conclusions Plasma pTau217 and pTau181 both correlate with AD, but the fold-change in pTau217 make it better to diagnose cerebral amyloidosis, and predict cognitive decline and conversion to AD dementia.