The amount of a alpha-N-acetylneuraminate alpha-2,8-sialyltransferase ST8SIA3 when measured in blood serum. The trait is Ontology of Biological Attributes entry OBA_2043683 (level of sia-alpha-2,3-Gal-beta-1,4-GlcNAc-R:alpha 2,8-sialyltransferase in blood serum). Also known as: blood serum alpha-N-acetylneuraminate alpha-2,8-sialyltransferase ST8SIA3 amount.