Study of the utility and impact of a plasma p‐tau181 Alzheimer's biomarker (SUITABLE)

Abstract INTRODUCTION Blood‐based Alzheimer's disease (AD) biomarkers are increasingly used in clinical care, but there are few real‐world studies of their clinical utility. We evaluated the impact of plasma phosphorylated tau at threonine 181 (p‐tau181) on the diagnosis and management of patients with cognitive impairment in a memory clinic. METHODS Dementia specialists referred patients for plasma p‐tau181 testing during clinical care. We used surveys and chart review to assess the impact of plasma p‐tau181 testing on clinical care and patient and care partner wellbeing. We assessed co‐primary outcomes of (1) change in diagnostic confidence before vs after testing, (2) change in diagnosis, and (3) change in management. A diagnosis or management change of greater than 30% was considered to be clinically significant. Secondary and exploratory outcomes included impact of plasma p‐tau181 testing on the use of additional diagnostics and impact on patient and care partner psychological wellbeing, health behaviors, and future planning. RESULTS One hundred patients completed plasma p‐tau181 testing; 81% had an elevated result, and 19% had a non‐elevated result. Clinician diagnostic confidence averaged 1.43 points higher after p‐tau181 testing (95% confidence interval CI 1.02 to 1.84, p < 0.0001). After testing, 27.7% (95% CI 18.9% to 36.4%, p = 0.31) of patients had a change in management and 17.2% of patients had a change in diagnosis – significantly lower than the 30% threshold (95% CI 9.5% to 24.9%, p = 0.004). Patients with elevated results were less likely to have a diagnosis changed after testing than those with non‐elevated results (OR 0.08 95% CI 0.01 to 0.47, p = 0.005). A non‐elevated result was associated with decreased use of amyloid positron emission tomography (PET) (odds ratio OR 0.25 95% CI 0.07 to 0.86, p = 0.028). Patients with an elevated result had higher anxiety at 2 to 3 months after disclosure ( p = 0.01). DISCUSSION Non‐elevated plasma p‐tau181 results impacted the diagnosis and use of amyloid PET imaging in a memory clinic. There was increased anxiety in patients after testing, affirming the need for post‐disclosure psychological support.