The amount of a galactosylgalactosylxylosylprotein 3-beta-glucuronosyltransferase 1 when measured in blood serum. The trait is level of galactosylgalactosylxylosylprotein 3-beta-glucuronosyltransferase 1 in blood serum (OBA_2040300). Also known as: blood serum galactosylgalactosylxylosylprotein 3-beta-glucuronosyltransferase 1 amount.