Prostaglandin D2-d4 (PGD2-d4) is primarily used as an internal standard in analytical chemistry, particularly in mass spectrometry and chromatography studies. It aids in the accurate quantification of prostaglandin D2 (PGD2) in biological samples, ensuring precision in research involving inflammation, allergic responses, and other physiological processes. This deuterated compound is essential for tracing metabolic pathways and understanding the role of PGD2 in various diseases, such as asthma and atopic dermatitis. Its application is critical in pharmacokinetic studies, enabling researchers to monitor drug interactions and therapeutic outcomes effectively.