Leukotriene C4-d5 (LTC4-d5) is primarily used as an internal standard in analytical chemistry, particularly in mass spectrometry-based studies. It aids in the accurate quantification of leukotriene C4 in biological samples, ensuring precise measurement and validation of results. This deuterated compound is essential in research focused on inflammation, asthma, and allergic responses, as it helps track and analyze the role of leukotrienes in these processes. Its application is critical in pharmacokinetic and pharmacodynamic studies, enabling researchers to understand drug interactions and therapeutic efficacy in treating inflammatory diseases.