The amount of a phosphatidylethanolamine O-18:1_20:4 when measured in blood serum. The trait is level of Phosphatidylethanolamine (O-18:1_20:4) in blood serum (OBA_2045148). Also known as: blood serum phosphatidylethanolamine O-18:1_20:4 amount, level of phosphatidylethanolamine O-18:1_20:4 in blood serum.