The amount of a Phosphatidylcholine (O-16:1_20:4) when measured in blood serum. The trait is level of Phosphatidylcholine (O-16:1_20:4) in blood serum (OBA_2045123, an Ontology of Biological Attributes entry). Also known as: blood serum Phosphatidylcholine (O-16:1_20:4) amount.