The amount of a CMP-N-acetylneuraminate-beta-galactosamide-alpha-2,3-sialyltransferase 1 when measured in blood serum. The trait is Ontology of Biological Attributes entry OBA_2044500 (level of CMP-N-acetylneuraminate-beta-galactosamide-alpha-2,3-sialyltransferase 1 in blood serum). Also known as: blood serum CMP-N-acetylneuraminate-beta-galactosamide-alpha-2,3-sialyltransferase 1 amount.