Comparison of ELISA- and SIMOA-based quantification of plasma Aβ ratios for early detection of cerebral amyloidosis

Abstract

Background Blood-based amyloid biomarkers may provide a non-invasive, cost-effective and scalable manner for detecting cerebral amyloidosis in early disease stages. Methods In this prospective cross-sectional study, we quantified plasma Aβ1–42/Aβ1–40 ratios with both routinely available ELISAs and novel SIMOA Amyblood assays, and provided a head-to-head comparison of their performances to detect cerebral amyloidosis in a nondemented elderly cohort (n = 199). Participants were stratified according to amyloid-PET status, and the performance of plasma Aβ1–42/Aβ1–40 to detect cerebral amyloidosis was assessed using receiver operating characteristic analysis. We additionally investigated the correlations of plasma Aβ ratios with amyloid-PET and CSF Alzheimer’s disease biomarkers, as well as platform agreement using Passing-Bablok regression and Bland-Altman analysis for both Aβ isoforms. Results ELISA and SIMOA plasma Aβ1–42/Aβ1–40 detected cerebral amyloidosis with identical accuracy (ELISA: area under curve (AUC) 0.78, 95% CI 0.72–0.84; SIMOA: AUC 0.79, 95% CI 0.73–0.85), and both increased the performance of a basic demographic model including only age and APOE-ε4 genotype (p ≤ 0.02). ELISA and SIMOA had positive predictive values of respectively 41% and 36% in cognitively normal elderly and negative predictive values all exceeding 88%. Plasma Aβ1–42/Aβ1–40 correlated similarly with amyloid-PET for both platforms (Spearman ρ = − 0.32, p < 0.0001), yet correlations with CSF Aβ1–42/t-tau were stronger for ELISA (ρ = 0.41, p = 0.002) than for SIMOA (ρ = 0.29, p = 0.03). Plasma Aβ levels demonstrated poor agreement between ELISA and SIMOA with concentrations of both Aβ1–42 and Aβ1–40 measured by SIMOA consistently underestimating those measured by ELISA. Conclusions ELISA and SIMOA demonstrated equivalent performances in detecting cerebral amyloidosis through plasma Aβ1–42/Aβ1–40, both with high negative predictive values, making them equally suitable non-invasive prescreening tools for clinical trials by reducing the number of necessary PET scans for clinical trial recruitment. Trial registration EudraCT 2009-014475-45 (registered on 23 Sept 2009) and EudraCT 2013-004671-12 (registered on 20 May 2014, https://www.clinicaltrialsregister.eu/ctr-search/trial/2013-004671-12/BE).

Highly specific and ultrasensitive plasma test detects Abeta(1–42) and Abeta(1–40) in Alzheimer’s disease

“…A next step in the development of these assays is to leverage the multiplexing possibilities of Simoa technology and simultaneously detect multiple biomarkers, to reflect different aspects of AD within one assay run, saving time and resources. It is to note, that the results presented in this study, together with the conducted diagnostic Amyblood studies 18 , 29 , 30 , resulted in the development of the neurology 4-plex E assay kit by Quanterix, incorporating the Amyblood assays together with the glial fibrillary acidic protein and neurofilament light assays. This availability enables independent and widespread validation.…”

“…We found that the ELISA ratio could not differentiate AD from controls, but the ELISA Abeta 1-42 concentration alone could. A recent study comparing the performance of the Abeta 1-42/1–40 ratio measured with the Amyblood assays and Euroimmun ELISA in non-demented elderly found that both assays could differentiate between amyloid-PET positive and negative participants with similar accuracy 18 . Other studies have also shown that ELISA Abeta 42 or the Abeta 42/40 ratio could differentiate between amyloid positive (either by CSF or PET) and negative participants 18 – 25 .…”

“…A recent study comparing the performance of the Abeta 1-42/1–40 ratio measured with the Amyblood assays and Euroimmun ELISA in non-demented elderly found that both assays could differentiate between amyloid-PET positive and negative participants with similar accuracy 18 . Other studies have also shown that ELISA Abeta 42 or the Abeta 42/40 ratio could differentiate between amyloid positive (either by CSF or PET) and negative participants 18 – 25 . Similar to other studies, we found no correlation between CSF Abeta 1-42 and plasma Abeta 42 concentrations, and only a weak correlation with the plasma Abeta 1-42/1–40 ratio 5 , 6 , 20 , 25 .…”

“…We carefully selected controls with normal CSF biomarker values, who are not likely to convert 28 . We wish to stress that the focus of our study was to compare analytical performance and clinical samples were included to indicate potential clinical value, since other studies are conducted on early diagnostic use of the Amyblood assays 18 , 29 , 30 .…”

The informed road map to prevention of Alzheimer Disease: A call to arms

“…Finally, the discovery and validation of AD bloodbased biomarkers, made possible with the development of novel techniques (e.g. immunoprecipitation-mass spectrometry or the high-precision immunoassays) [23,25,[99][100][101] will offer major opportunities for screening and enrollment of potential participants for primary and secondary prevention trials, reducing trial duration and costs due to screen failures.…”