IL6 and Sepsis: Compared to the relatively short half-lives of cytokines such as tumor necrosis factor (TNF)-a and interleukin (IL)-6, the half-life of serum PCT in the systemic circulation is 25-30 hours rather long.[22] Because of these properties, serum PCT has been proposed as an indicator of severe generalized infections or sepsis.[4, 5, 23]