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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.

Author information

1
Quest Diagnostics Nichols Institute, San Juan Capistrano, CA.
2
Quest Diagnostics, Marlborough, MA.
3
Quest Diagnostics, San Leandro, CA.
4
University of California, San Diego (UCSD) ADRC Neuropathology Core and Brain Bank, La Jolla, CA.
5
Veterans Affairs San Diego Healthcare System, La Jolla, CA.
6
UC San Diego Department of Neurosciences and Shiley Marcos Alzheimer's Disease Research Center, La Jolla, CA.
7
Quest Diagnostics Nichols Institute, San Juan Capistrano, CA; Nigel.J.Clarke@questdiagnostics.com.

Abstract

BACKGROUND:

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.

METHODS:

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.

RESULTS:

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.

CONCLUSIONS:

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

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