Predicting continuous amyloid PET values with CSF and plasma A beta 42/A beta 40

Introduction: Continuous measures of amyloid burden as measured by positron emission tomography (PET) are being used increasingly to stage Alzheimer's disease (AD). This study examined whether cerebrospinal fluid (CSF) and plasma amyloid beta (A13)42/A1340 could predict continuous values for amyloid PET.Methods: CSF A1342 and A1340 were measured with automated immunoassays. Plasma A1342 and A1340 were measured with an immunoprecipitation-mass spectrometry assay. Amyloid PET was performed with Pittsburgh compound B (PiB). The continuous relationships of CSF and plasma A1342/A1340 with amyloid PET burden were modeled.Results: Most participants were cognitively normal (427 of 491 [87%]) and the mean age was 69.0 +/- 8.8 years. CSF A1342/A1340 predicted amyloid PET burden until a relatively high level of amyloid accumulation (69.8 Centiloids), whereas plasma A1342/A1340 predicted amyloid PET burden until a lower level (33.4 Centiloids).Discussion: CSF A1342/A1340 predicts the continuous level of amyloid plaque burden over a wider range than plasma A1342/A1340 and may be useful in AD staging.