tetranor-PGEM is the major urinary metabolite of PGE1 and PGE2, and is used as a marker of PGE2 biosynthesis.[1],[2] About 15% of an infused dose of PGE2 appears as this metabolite in the urine of humans. Normal healthy males excrete 7-40 μg of tetranor-PGEM over a 24-hour period.[1]