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

BACKGROUND: 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. HYPOTHESIS/OBJECTIVES: 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. ANIMALS: Forty-eight critically ill dogs and 24 healthy control dogs. METHODS: 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. RESULTS: 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. CONCLUSIONS AND CLINICAL IMPORTANCE: Critically ill dogs have altered amino acid profiles and additional research to investigate potential benefits of amino acid supplementation is warranted.