The amount of a serine/threonine-protein phosphatase 4 catalytic subunit when measured in blood serum. The trait is level of serine/threonine-protein phosphatase 4 catalytic subunit in blood serum (OBA_2043013, an Ontology of Biological Attributes identifier). Also known as: blood serum serine/threonine-protein phosphatase 4 catalytic subunit amount.