Feasibility and validity of using self-collected capillary blood using Tasso+ for measuring Alzheimer's Disease plasma-based biomarkers among underrepresented populations.

Background: Blood-based biomarkers offer a scalable alternative to cerebrospinal fluid and PET imaging for Alzheimer's disease (AD) detection, yet traditional venipuncture limits participation among rural and socioeconomically disadvantaged populations. Self-collection using the Tasso+ capillary device could reduce access barriers, but its feasibility and validity for AD plasma biomarkers remain uncertain, particularly with real-world delays prior to processing. Methods: Adults aged 45-90 years from the Wisconsin SHOW cohort who were underrepresented in AD research (Black or Hispanic race/ethnicity, rural residence, or <bachelor's degree) were recruited (n=28). At community "pop-up" clinics participants completed: (1) self-collection of capillary blood via Tasso+; (2) experience surveys; (3) Montreal Cognitive Assessment; and (4) standard venipuncture. To simulate home-based collection and mail return, Tasso+ samples were held at room temperature for 24 hours before centrifugation, whereas venous samples were processed within 30 minutes. Plasma Aβ40, Aβ42, Aβ42/40, GFAP, NfL, and pTau217 were measured on the Quanterix Simoa platform. Between-method agreement was evaluated using Pearson/Spearman correlations, Lin's concordance correlation coefficients (CCC), Bland-Altman analyses, and relative bias. Predictors of percent difference were explored with univariate regression. Results: Tasso+ collection was successful for 96% of participants; 64% rated it very easy and 86% reported comfort/no pain, yet 57% preferred future venipuncture-particularly Black, lower-income, and lower-education participants. Agreement varied markedly by biomarker. GFAP and NfL demonstrated excellent concordance (CCC 0.97-0.98) with minimal bias (-6% to -8%). Aβ40 and Aβ42 showed modest correlations (r=0.40-0.47) and substantial underestimation (-60% to -70%). Aβ42/40 and pTau217 exhibited poor correlation and extreme positive bias for pTau217 (~+2600%). Hemolysis was more frequent in Tasso+ samples and contributed to disagreement for several markers; processing lag and sample volume were not strong predictors. Conclusions: Remote capillary self-collection with a 24-hour delay is suitable for measuring GFAP and NfL but not currently reliable for Aβ or pTau217 without improved handling (e.g., temperature control, hemolysis reduction). Although user experience was favorable, trust and logistical concerns limited preference among underrepresented groups. Community-informed strategies and optimized pre-analytics are essential before deploying Tasso+ in large AD studies.