OCA2 and early-onset autosomal dominant Alzheimer disease: Although both plasma and serum have been utilized for measuring Aβ levels, comparisons of biomarker levels in the context of Alzheimer’s disease clinical research specifically have shown that some analytes, including Aβ peptides, t-tau, and multiple p-tau species present in lower levels in serum potentially attributed to loss from clot trapping (99–104).