The complement system is an important factor in innate immunity. During complement activation of complement protein 5 (C5), C5 is proteolytically cleaved and the anaphylatoxic peptide C5a is generated. C5a is a small polypeptide consisting of 74 aminoacids (11kDa) and is derived from the N-terminus of the alpha chain. C5a itself is very short-lived and in serum is cleaved rapidly into the more stable, though biologically still active C5a-desArg (also called acylation stimulating protein, ASP. Therefore, measurement of C5a-desArg allows reliable conclusions about the level of complement activation in the test samples. For convenience, both forms will be referred to in the following text as C5a. C5a acts as a potent anaphylatoxin causing smooth muscle contraction, vasodilation, increased vascular permeability, basophil and mast cell degranulation and lysosomal enzyme release. In addition, C5a is a potent chemotactic factor for eosinophils, basophils and monocytes.C5a is involved in inflammatory reactions seen in gram-negative bacterial sepsis, trauma, ischemic heart disease, post-dialysis syndrome and a variety of autoimmune diseases. Elevation of C5a is associated with increased cardiovascular risk in patients with advanced atherosclerosis. Also, C5a is closely associated with the capillary leak syndrome in leukemic children after bone marrow transplantation. C5a is also a marker in urine for predicting the onset of acute graft rejection after kidney transplantation. Activation products of the complement cascade contain neo-epitopes that are not present in the individual native components. The human C5a ELISA kit is based on a catching monoclonal antibody that recognizes a neo-epitope on C5a-desArg. This prevents cross-reactivity with C5