(7S,23Z)-4-hydroxy-7-[(1R,2E)-1-hydroxy-2-hexadecen-1-yl]-N,N,N-trimethyl-9-oxo-3,5-dioxa-8-aza-4-phosphadotriacont-23-en-1-aminium 4-Oxide Inner Salt 4-Oxide-d17 is the labeled analogue of (7S,23Z)-4-hydroxy-7-[(1R,2E)-1-hydroxy-2-hexadecen-1-yl]-N,N,N-trimethyl-9-oxo-3,5-dioxa-8-aza-4-phosphadotriacont-23-en-1-aminium 4-Oxide Inner Salt (H809780), one of the 25 key sphingolipids and phosphosphingolipids in human plasma.