A retrospective analysis of 194 consecutive patients referred for amyloid PET at a memory clinic compared positivity across subjective cognitive decline, mild cognitive impairment and early Alzheimer's disease. Positivity rose stepwise from 40.9% to 66.0% to 91.7%, with Centiloid and regional uptake rising in parallel, most in temporal cortex and precuneus. Adding structural MRI indices to clinical diagnosis left discrimination unchanged, at a cross-validated area under the curve of 0.752 against 0.751.
Why it is interesting: It quantifies how far biological positivity runs ahead of clinical diagnosis in the group with complaints but no measured impairment, which is where a biologically defined case count would expand.