Affiliations: [a] Department of Ophthalmology and Visual Sciences, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
| [b] Department of Population Health Sciences, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
Correspondence:
[*]
Correspondence to: Carla R. Schubert, MS, Department of Ophthalmology and Visual Sciences, 610 Walnut Street, Rm 1087 WARF, Madison, WI 53726, USA. Tel.: +1 608 265 3722; E-mail: schubert@episense.wisc.edu.
Abstract: Background: Stored blood samples from longitudinal cohort studies may be useful for studying biomarkers of preclinical Alzheimer’s disease. Objective: This study aimed to determine the reliability of amyloid-β40 and amyloid-β42 (Aβ40, Aβ42), total tau (TTau), and neurofilament light (NfL) concentrations measured in blood samples stored long-term at -80°C. Methods: Aβ40, Aβ42, TTau, and NfL were measured in serum and plasma samples from two longitudinal cohort studies. Serum samples had been stored at -80°C for 5 (n = 24), 14 (n = 24), and 20 years (N = 78) and plasma samples had been stored for 16 years (N = 78). Biomarker concentrations were measured in duplicate using a single molecule array assay (Simoa; Quanterix, Billerica, MA). Replicate samples for each sample type and storage length were included. Results: The concentrations of Aβ40, Aβ42, TTau, and NfL were within expected ranges. Some serum TTau concentrations were below the limit of detection. The average intra-assay coefficients of variation (CV) for duplicate measures were 2–7% for all assays except for serum TTau, which were higher (CVs 13% and 17%). Mean differences in original replicate pair Aβ40, Aβ42, and NfL concentrations were slightly greater in samples stored for longer versus shorter time periods. Conclusion: Aβ40, Aβ42, TTau, and NfL can be measured in serum and plasma samples that have been stored up to 20 years at -80°C. Long-term storage may be associated with small increases in the variability of concentrations in samples stored 14 or more years.
Keywords: Alzheimer’s disease, amyloid-β, blood biomarkers, epidemiology, neurofilament light, plasma, serum, single molecule array, total tau
