Plasma amyloid assay as a pre-screening tool for amyloid positron emission tomography imaging in early stage Alzheimer's disease

Introduction Due to the high cost and high failure rate of ascertaining amyloid positron emission tomography positivity (PET+) in patients with earlier stage Alzheimer's disease (AD), an effective pre-screening tool for amyloid PET scans is needed. Methods Patients with mild cognitive impairment (n = 33, 24.2% PET+, 42% females, age 74.4 +/- 7.5, MMSE 26.8 +/- 1.9) and mild dementia (n = 19, 63.6% PET+, 36.3% females, age 73.0 +/- 9.3, MMSE 22.6 +/- 2.0) were recruited. Amyloid PET imaging, Apolipoprotein E (APOE) genotyping, and plasma amyloid beta (A beta)(1-40), A beta(1-42), and total tau protein quantification by immunomagnetic reduction (IMR) method were performed. Receiver operating characteristics (ROC) analysis and Youden's index were performed to identify possible cut-off points, clinical sensitivities/specificities, and areas under the curve (AUCs). Results Amyloid PET+ participants had lower plasma A beta(1-42) levels than amyloid PET-negative (PET-) subjects. APOE epsilon 4 carriers had higher plasma A beta(1-42) than non-carriers. We developed an algorithm involving the combination of plasma A beta(1-42) and APOE genotyping. The success rate for detecting amyloid PET+ patients effectively increased from 42.3 to 70.4% among clinically suspected MCI and mild dementia patients. Conclusions Our results demonstrate the possibility of utilizing APOE genotypes in combination with plasma A beta(1-42) levels as a pre-screening tool for predicting the positivity of amyloid PET findings in early stage dementia patients.