level of polypeptide N-acetylgalactosaminyltransferase 4 in blood serum (Ontology of Biological Attributes entry OBA_2041666) is the amount of a polypeptide N-acetylgalactosaminyltransferase 4 when measured in blood serum. Also known as: blood serum polypeptide N-acetylgalactosaminyltransferase 4 amount.