Real world diagnostic performance of plasma p-tau217 for early-onset Alzheimer's disease in a cognitive disorders tertiary care setting

Background: Plasma p-tau217 shows exceptional diagnostic performance for Alzheimer's disease (AD) in cohort studies. Recent real-world studies support its validity in more diverse populations. Objective: Test the performance of plasma p-tau217 in representative real-world early-onset cognitive disorders patients.Methods118 adult patients with cognitive complaints or potential neurodegenerative diseases (ND) from a single healthcare network in Melbourne, Australia, were categorized into three groups based on clinical diagnosis: non-ND (n = 52), early-onset AD (EOAD, n = 39), and non-AD ND (other-ND, n = 27). Plasma p-tau217 was measured using the Simoa® ALZpath p-Tau 217 Assay. Results: Plasma p-tau217 was elevated in EOAD (mean ± SD: 1.13 ± 0.51) compared with non-ND (0.31 ± 0.27, p = 5.43e-23) and other-ND (0.23 ± 0.10, p = 9.65e-21). ROC analysis revealed excellent diagnostic performance, with AUCs of 0.944 [95% CI:0.893-0.996] for EOAD versus non-ND and 0.984 [0.962-1.000] for EOAD versus other-ND. Using a binary cut-off (p-tau217 > 0.42 pg/mL), 17% non-ND, 95% EOAD and 7% other-ND were A + . Using a two-tiered cut-off approach (0.40 pg/mL > p-tau217 > 0.63 pg/mL), 4% non-ND, 94% EOAD and 0% other-ND were A + . 10% of participants (n = 12) were within the intermediate range. Using the binary cut-off of p-tau217 > 0.64 pg/mL for T+, 100% EOAD and 0% other-ND A + participants, defined by the two-tiered cut-off approach, were T + . No associations of p-tau217 with age, sex, or ethnicity were found within ND groups. P-tau217 was elevated in individuals with severely impaired renal function. Conclusions: The findings support the clinical utility of plasma p-tau217 in the real-world diagnostic evaluation of EOAD. However, careful interpretation of false positive results in patients with severe renal impairment is required.