Amyloid PET Utilization and Diagnostic Yield Before and After Routine Plasma Oligomerized Amyloid-β Testing in a Memory Clinic

Background/Objectives: Blood-based biomarkers may help prioritize patients for confirmatory amyloid testing. We compared amyloid positron emission tomography (PET) utilization and diagnostic yield between memory-clinic periods before and after plasma oligomerized amyloid-β (oAβ) testing became routinely available. Methods: This retrospective, single-center, before-and-after cohort study included 1125 index evaluations for cognitive complaints (660 pre-oAβ; 465 post-oAβ). The primary outcome was PET diagnostic yield, defined as the proportion of amyloid-positive scans among patients undergoing 18F-florapronol PET. Secondary analyses assessed PET utilization, PET examinations per amyloid-positive case, and, within the post-oAβ period, the association between oAβ ≥ 0.78 ng/mL and subsequent PET use. Results: PET utilization did not differ significantly between the post- and pre-oAβ periods (10.1% vs. 7.7%; odds ratio [OR], 1.34; 95% confidence interval [CI], 0.89–2.03; p = 0.165). PET diagnostic yield was higher in the post-oAβ period (78.7% vs. 33.3%; OR, 7.40; 95% CI, 2.98–18.37; p < 0.001), including after adjustment for age and sex (adjusted OR [aOR], 6.89; 95% CI, 2.74–17.29). PET examinations per amyloid-positive case were 1.27 and 3.00, respectively. Within the post-oAβ period, oAβ ≥ 0.78 ng/mL was associated with subsequent PET use (aOR, 2.78; 95% CI, 1.49–5.18), with similar estimates after multiple imputation of missing covariates. Conclusions: Amyloid PET yield was higher after routine oAβ testing was introduced than before, without a significant increase in PET use. Because anti-amyloid treatment awareness and referral practices also changed over time, this difference cannot be attributed to oAβ testing itself, and the higher yield does not indicate improved assay accuracy. These findings support prospective evaluation of blood-biomarker-guided triage.