tetranor-PGDM-d6 contains six deuterium atoms at the 17, 17', 18, 18', 19 and 19' positions. It is intended for use as an internal standard for the quantification of tetranor-PGDM by GC- or LC-mass spectrometry (MS). Prostaglandin D2 (PGD2) is synthesized by hematopoietic-type PGD-synthase (H-PGDS) in mast cells and is released in large quantities during allergic and asthmatic anaphylaxis.¹ PGD2 is also produced in the brain by lipocalin PGD-synthase also known as β-trace.^2,3 In the brain, PGD2 produces normal physiological sleep and lowering of body temperature.^2,3 Further pharmacological actions include inhibition of platelet aggregation and relaxation of vascular smooth muscle.⁴ tetranor-PGDM is a major metabolite of PGD2 that is detectable in human and murine urine.⁵ The levels of tetranor-PGDM and 2,3-dinor-11b-PGF2α, a related PGD2 metabolite, in human urine were found to be 1.5 ± 0.3 and 0.6 ± ng/mg creatinine, respectively. tetranor-PGDM was detected in mouse urine at a level of 8.1 ± 1.3 ng/mg creatinine.⁵