Earlier Disclosure of Blood-Based Biomarkers, Diagnostic Certainty, and Clinical Management: A Randomized Clinical Trial.

Importance: Blood-based biomarkers show high performance for detecting Alzheimer disease (AD) pathology, but evidence on their impact on diagnostic certainty, clinical management, and emotional outcomes in routine care is limited. Objective: To determine whether earlier disclosure of plasma phosphorylated tau at threonine 217 (p-tau217) and neurofilament light chain (NfL) increases etiologic diagnostic certainty, influences clinical management, and affects emotional outcomes in individuals evaluated for cognitive symptoms. Design, Setting, and Participants: This was a prospective randomized clinical trial conducted at a single memory clinic in Spain between February and October 2024, with 9 months of follow-up. Consecutive new outpatients with subjective cognitive decline (SCD), mild cognitive impairment (MCI), or mild dementia without a prior etiologic diagnosis were enrolled. Of 265 eligible participants, 220 were randomized to earlier disclosure of blood-based biomarkers at the 3-month visit or delayed disclosure at the 9-month visit. Intervention: Disclosure of blood-based biomarkers for AD pathology (p-tau217) and neurodegeneration (NfL) to the treating neurologist and participant, alongside standard clinical evaluation. Main Outcomes and Measures: The primary outcome was the proportion of participants achieving a very high-confidence etiologic diagnosis (≥90%). Secondary outcomes included changes in clinical management and emotional outcomes (anxiety, depression, perceived stress, and quality of life). Results: Among the 220 randomized participants (median [IQR] age, 73 [68-78] years; 123 [55.9%] women), baseline diagnoses were SCD (100 [45.5%]), MCI (68 [30.9%]), and mild dementia (52 [23.6%]). At 3 months, a very high-confidence etiologic diagnosis was achieved in 56 of 112 participants in the earlier-disclosure arm (50.0%) compared with 5 of 108 in the delayed-disclosure arm (4.6%) (P < .001). Diagnostic certainty converged after disclosure in both arms, except among participants with MCI, in whom higher certainty persisted in the earlier-disclosure arm. Earlier disclosure was associated with more frequent initiation of symptomatic AD treatment (16/112 [14.3%] vs 5/108 [4.6%]; difference, 9.7; 95% CI, 1.8 to 17.8; P = .01), fewer planned follow-up neuropsychological reassessments for diagnostic clarification (34/112 [30.4%] vs 57/108 [52.8%]; difference, -22.4; 95% CI, -34.4 to -9.4; P < .001), and more planned discharge from the memory clinic to primary care (35/112 [31.3%] vs 13/108 [12.0%]; difference, 19.2; 95% CI, 8.4 to 29.5; P < .001). Earlier disclosure was not associated with worse emotional outcomes. Conclusions and Relevance: In this randomized clinical trial, earlier disclosure of blood-based biomarkers increased etiologic diagnostic certainty and led to earlier, targeted clinical management without increasing emotional distress. These findings support the integration of blood-based biomarkers into memory clinic diagnostic pathways. Trial Registration: ClinicalTrials.gov Identifier: NCT06246019.