Confounding factors of Alzheimer's disease plasma biomarkers and their impact on clinical performance.

Introduction: Plasma biomarkers will likely revolutionize the diagnostic work‐up of Alzheimer's disease (AD) globally. Before widespread use, we need to determine if confounding factors affect the levels of these biomarkers, and their clinical utility. Methods: Participants with plasma and CSF biomarkers, creatinine, body mass index (BMI), and medical history data were included (BioFINDER‐1: n = 748, BioFINDER‐2: n = 421). We measured beta‐amyloid (Aβ42, Aβ40), phosphorylated tau (p‐tau217, p‐tau181), neurofilament light (NfL), and glial fibrillary acidic protein (GFAP). Results: In both cohorts, creatinine and BMI were the main factors associated with NfL, GFAP, and to a lesser extent with p‐tau. However, adjustment for BMI and creatinine had only minor effects in models predicting either the corresponding levels in CSF or subsequent development of dementia. Discussion: Creatinine and BMI are related to certain plasma biomarkers levels, but they do not have clinically relevant confounding effects for the vast majority of individuals. Highlights: Creatinine and body mass index (BMI) are related to certain plasma biomarker levels.Adjusting for creatinine and BMI has minor influence on plasma‐cerebrospinal fluid (CSF) associations.Adjusting for creatinine and BMI has minor influence on prediction of dementia using plasma biomarkers. [ABSTRACT FROM AUTHOR]