Classification accuracies of plasma ptau217 vs. ptau217/Aβ1-42 for brain Aβ pathology in cognitively normal older adults

Alzheimer´s Disease (AD) and neurodegenerative blood-based biomarkers (BBMs) are transitioning from research settings to clinical practice, where accurate interpretation is critical for their appropriate use. Particularly, the limited alignment between AD pathology and metrics of cognitive performance suggest unappreciated factors of resilience or inter-individual variability that could be influencing clinical utility and interpretation of these measures. Ninety-one cognitively normal older adults from the AGUEDA trial (NCT05186090) (71.8 ± 3.9 years; 58% females) were cross-sectionally examined for plasma Aβ42/40 SIMOA, BD-tau, GFAP, NfL, ptau217, ptau181, ptau217/Aβ1-42 IPMS and ptau217/Aβ42 SIMOA. We evaluated BBMs classification accuracies for brain amyloid-beta and examined their associations with cognitive outcomes. We then examined whether selected individual characteristics impact BBMs. Ptau217 and ptau217/Aβ42 measured by both IPMS and SIMOA exhibited strong predictive accuracy for PET Aβ positivity (AUC > 0.8) with the inclusion of some individual characteristics lowering their accuracy. Episodic memory showed a positive association with BD-tau (r = 0.29; p = 0.018), attentional/inhibitory control correlated positively with ptau217/Aβ42 SIMOA (r = 0.26; p = 0.041) and processing speed was negatively linked to GFAP (r = -0.21; p = 0.047). Age, creatinine, depressive symptoms, comorbidities and sex were associated with BD-tau, GFAP, NfL, and ptau217/Aβ42 (both IPMS and SIMOA), with standardized β values ranging from -0.27 to 0.62 (all p < 0.05). These results highlight the utility of ptau217 and ptau217/Aβ42 ratios in identifying brain amyloid pathology in cognitively normal older adults. BBMs could be used complementarily to support differential diagnosis and better understand the origins of cognitive deficits.