Because of the rapid metabolism of PGE2, the determination of in vivo PGE2 biosynthesis is often best accomplished by the measurement of PGE2 metabolites. Cayman's PGEM Assay converts all 13,14-dihydro-15-keto PGE2 and 13,14-dihydro-15-keto PGA2 into a single stable derivative, which is easily measurable by ELISA. This assay is therefore the method of choice if the samples in question have undergone extensive metabolism prior to collection.