Serum unconjugated bile acids as a test for intestinal bacterial overgrowth in dogs

Small intestinal bacterial overgrowth (SIBO) has a high incidence in dogs and, as in humans, is difficult to diagnose. The aim of this study was to determine the diagnostic significance of serum unconjugated bile acid concentrations in dogs with bacterial overgrowth. Fasting sera were obtained from 23 dogs: 10 with culture-proven SIBO, 8 with indirectly diagnosed SIBO (normal pancreatic function but small intestinal disease associated with subnormal serum cobalamin and supranormal folate concentrations), and 5 healthy controls. Unconjugated bile acids were determined using gas chromatography-mass spectrometry after isolation by liquid-solid extraction and anion-exchange chromatography. Mean serum unconjugated bile acid concentrations were significantly elevated in dogs with SIBO (mean +/- SD: 0.91 +/- 1.03 micromol/liter), and in dogs with indirectly diagnosed SIBO (2.11 +/- 2.20 micromol/liter) compared to clinically healthy dogs (0.015 +/- 0.015 micromol/liter, P < 0.005). Cholic acid was the predominant unconjugated bile acid in the serum of dogs with SIBO. In conclusion serum unconjugated bile acid concentrations of healthy dogs are significantly lower than reported values for humans, and this fraction represents a relatively small proportion (0-2.3%; mean 0.8%) of the total bile acids in dogs. Unconjugated bile acids increased 10- to 20-fold in dogs with SIBO indicating the clinical utility of serum unconjugated bile acids for diagnosis of intestinal bacterial overgrowth in dogs.