Relationship among Plasma Amino Acids, C-Reactive Protein, Illness Severity, and Outcome in Critically Ill Dogs

Alterations in circulating amino acids have been documented in animal models and in critically ill people but have not been evaluated in dogs with spontaneously occurring disease. To compare amino acid concentrations in critically ill dogs and healthy controls and to investigate potential relationships among amino acids, markers of inflammation, illness severity, and clinical outcome. Forty-eight critically ill dogs and 24 healthy control dogs. Plasma was analyzed for amino acids and C-reactive protein (CRP) was measured in serum. The Fischer ratio (the molar ratio of branched chain amino acids [BCAA] to aromatic amino acids [AAA]) and survival prediction index (SPI2) were calculated. Median CRP concentrations were significantly higher in the critically ill dogs compared with controls (P < .001). Critically ill dogs had significantly lower concentrations of alanine (P = .001), arginine (P < .001), citrulline (P < .001), glycine (P < .001), methionine (P < .001), proline (P < .001), and serine (P = .001) but significantly higher concentrations of lysine (P = .02) and phenylalanine (P < .001; Table 1). This pattern resulted in a significantly lower Fischer ratio (P = .001) in the critically ill group. Median SPI2 score was significantly higher in dogs that survived (P = .03). Concentrations of arginine (P = .02), isoleucine (P = .01), leucine (P = .04), serine (P = .04), valine (P = .04), total BCAA (P = .03), and the Fischer ratio (P = .03) were significantly higher in survivors compared with nonsurvivors. Critically ill dogs have altered amino acid profiles and additional research to investigate potential benefits of amino acid supplementation is warranted.