Abstract: A proteomic expression platform to identify age-related sepsis risk is disclosed using patients with an intra-abdominal infection. A semi-quantitative plasma proteomics workflow was applied which incorporated tandem immuno affinity depletion, iTRAQ labeling, strong cation exchange fractionation, and nanoflow-liquid chromatography coupled to high resolution mass spectrometry. A protein profile was determined that exhibit statistically significant differences in expression levels amongst patients with severe sepsis as a function of age. Representative pathways that are differentially-expressed include, but are not limited to, acute phase response, coagulation signaling, atherosclerosis signaling, lipid metabolism, and production of nitric oxide/reactive oxygen species.