IMPORTANCE Metabolomics is the broad and parallel study of metabolites within an organism and provides a contemporaneous snapshot of physiologic state. Use of metabolomics in the clinical settingmay help achieve precision medicine for those who have experienced trauma, where diagnosis and treatment are tailored to the individual patient. OBJECTIVE To examine whether metabolomics can (1) distinguish healthy volunteers from trauma patients and (2) quantify changes in catabolic metabolites over time after injury. DESIGN, SETTING, AND PARTICIPANTS Prospective cohort study with enrollment from September 2014 to May 2015 at an urban, level 1 trauma center. Included in the study were 10 patients with severe blunt trauma admitted within 12 hours of injury with systolic blood pressure less than 90mmHg or base deficit greater than 6mEq/L and 5 healthy volunteers. Plasma samples (n = 35) were obtained on days 1, 3, and 7, and they were analyzed using mass spectrometry. MAIN OUTCOMES AND MEASURES Principal component analyses, multiple linear regression, and paired t tests were used to select biomarkers of interest. A broad-based metabolite profile comparison between trauma patients and healthy volunteers was performed. Specific biomarkers of interest were oxidative catabolites. RESULTS Trauma patients had a median age of 45 years and a median injury severity score of 43 (interquartile range, 34-50). Healthy fasting volunteers had a median age of 33 years. Compared with healthy volunteers, trauma patients showed oxidative stress on day 1: niacinamide concentrations were a mean (interquartile range) of 0.95 (0.30-1.45) relative units for trauma patients vs 1.06 (0.96-1.09) relative units for healthy volunteers (P = .02), biotin concentrations, 0.43 (0.27-0.58) relative units for trauma patients vs 1.21 (0.93-1.56) relative units for healthy volunteers (P = .049); and choline concentrations, 0.17 (0.09-0.22) relative units for trauma patients vs 0.21 (0.18-0.22) relative units for healthy volunteers (P = .004). Trauma patients showed lower nucleotide synthesis on day 1: adenylosuccinate concentrations were 0.08 (0.04-0.12) relative units for trauma patients vs 0.15 (0.14-0.17) relative units for healthy volunteers (P = .02) and cytidine concentrations were 1.44 (0.95-1.73) relative units for trauma patients vs 1.74 (1.62-1.98) relative units for healthy volunteers (P = .05). From trauma day 1 to day 7, trauma patients showed increasing muscle catabolism: serine levels increased from 42.03 (31.20-54.95) μM to 79.37 (50.29-106.37) μM (P = .002), leucine levels increased from 69.21 (48.36-99.89) μM to 114.16 (92.89-143.52) μM (P = .004), isoleucine levels increased from 20.43 (10.92-27.41) μM to 48.72 (36.28-64.84) μM (P < .001), and valine levels increased from 122.56 (95.63-140.61) μM to 190.52 (136.68-226.07) μM(P = .004). There was an incomplete reversal of oxidative stress. CONCLUSIONS AND RELEVANCE Metabolomics can function as a serial, comprehensive, and potentially personalized tool to characterizemetabolism after injury. A targeted metabolomics approach was associated with ongoing oxidative stress, impaired nucleotide synthesis, and initial suppression of protein metabolism followed by increased nitrogen turnover. This technique may provide new therapeutic and nutrition targets in critically injured patients.