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Clin Chem. 2019 Dec;65(12):1572-1580. doi: 10.1373/clinchem.2018.300947. Epub 2019 Oct 18.

High-Throughput Mass Spectrometry Assay for Quantifying β-Amyloid 40 and 42 in Cerebrospinal Fluid.

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Quest Diagnostics Nichols Institute, San Juan Capistrano, CA.
Quest Diagnostics, Marlborough, MA.
Quest Diagnostics, San Leandro, CA.
University of California, San Diego (UCSD) ADRC Neuropathology Core and Brain Bank, La Jolla, CA.
Veterans Affairs San Diego Healthcare System, La Jolla, CA.
UC San Diego Department of Neurosciences and Shiley Marcos Alzheimer's Disease Research Center, La Jolla, CA.
Quest Diagnostics Nichols Institute, San Juan Capistrano, CA;



The ratio of β-amyloid 1-42 (Aβ42) to Aβ40 in cerebrospinal fluid (CSF) may be useful for evaluating Alzheimer disease (AD), but quantification is limited by factors including preanalytical analyte loss. We developed an LC-MS/MS assay that limits analyte loss. Here we describe the analytical characteristics of the assay and its performance in differentiating patients with AD from non-AD dementia and healthy controls.


To measure Aβ42/Aβ40, we used unique proteolytically derived C-terminal peptides as surrogate markers of Aβ40 and Aβ42, which were analyzed and quantified by LC-MS/MS. The assay was analytically validated and applied to specimens from individuals with clinically diagnosed AD (n = 102), mild cognitive impairment (n = 37), and non-AD dementias (n = 22), as well as from healthy controls (n = 130). Aβ42/Aβ40 values were compared with APOE genotype inferred from phenotype, also measured by LC-MS/MS.


The assay had a reportable range of 100 to 25000 pg/mL, a limit of quantification of 100 pg/mL, recoveries between 93% and 111%, and intraassay and interassay CV <15% for both peptides. An Aβ42/Aβ40 ratio cutoff of <0.16 had a clinical sensitivity of 78% for distinguishing patients with AD from non-AD dementia (clinical specificity, 91%) and from healthy controls (clinical specificity, 81%). The Aβ42/Aβ40 ratio decreased significantly (P < 0.001) with increasing dose of APOE4 alleles.


This assay can be used to determine Aβ42/Aβ40 ratios, which correlate with the presence of AD.

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