Krychtiuk KA, et al. - This prospective, observational study explored the link between circulating interleukin (IL)-33 and 30-day mortality in patients admitted to a medical intensive care unit (ICU). Findings revealed that mortality risk in these patients was predicted by low levels of IL-33 and increased levels of soluble ST2 (sST2), independent from each other and APACHE II score (acute physiology and chronic health evaluation II). A pathogenic role of the IL-33/ST2 system in critically ill patients was obvious as both together demonstrated additive predictive value.