The amount of a heparan sulfate glucosamine 3-O-sulfotransferase 3B1 when measured in blood serum. The trait is Ontology of Biological Attributes term OBA_2041932 (level of heparan sulfate glucosamine 3-O-sulfotransferase 3B1 in blood serum). Also known as: blood serum heparan sulfate glucosamine 3-O-sulfotransferase 3B1 amount.