The amount of a polypeptide N-acetylgalactosaminyltransferase 3 (human) when measured in blood. The trait is amount of polypeptide N-acetylgalactosaminyltransferase 3 (human) in blood (OBA_2052801, an Ontology of Biological Attributes id). Also known as: blood polypeptide N-acetylgalactosaminyltransferase 3 (human) amount.