The amount of a heparan sulfate glucosamine 3-O-sulfotransferase 3A1 when measured in blood serum. The trait is OBA_2041931 (level of heparan sulfate glucosamine 3-O-sulfotransferase 3A1 in blood serum). Also known as: blood serum heparan sulfate glucosamine 3-O-sulfotransferase 3A1 amount.