As serum bile acids testing is now often used as a screening test rather than for confirming hepatic dysfunction in ill patients, questions have arisen about the interpretation of results.

Results from fasting and post-prandial bile acids can vary or give spurious values due to:

• common presence of microvascular dysplasia (MVD). Bile acids can be intermittently high in these dogs, although they often are clinically normal. Certain breeds, such as Cairn Terriers and toy breeds, are predisposed to MVD.
• not all bile acids are stored in the gall bladder. Only ~60-80% of resting bile acids are in the gall bladder at any given time. Some bile acids are continuously released into the small intestine.
• gall bladder has periodic, small spontaneous contractions.
• incomplete post-prandial gall bladder contraction.
• variation in timing of peak bile acids concentration after feeding. Most dogs show maximum bile acids 2-4 hours post-prandially, although some dogs peak at 6-8 hours.
• delayed gastric emptying.
• differences in intestinal transit time.

These physiologic variations in the enterohepatic cycle explain why fasting bile acids sometimes can be higher than post-prandial bile acids. Such differences can be quite large, and fasting bile acids 100 µmol/L more than post-prandial concentrations can be seen.

Hepatic dysfunction is considered to be present when resting or post-prandial bile acids are greater than 25 µmol/L (dog) and 20 µmol/L (cat).

Animals with vascular shunts but normal hepatocytes tend to have lower and often normal fasting bile acids than do animals with hepatocellular disease.

• interpretation of changes in bile acids can be difficult.
• modest reduction in serum bile acids concentrations cannot be used to conclude there is improvement in liver function or reduction in liver disease.
• animals with chronic liver disease develop acquired vascular shunts that do not close, even if liver disease resolves. Thus, post-prandial bile acids likely will always be increased, despite improvement in liver function.
• ursodiol (Actigal™) cross-reacts with the bile acids test and so use of this drug can falsely elevate bile acids concentration. As ursodiol will saturate the bile acids pool with chronic use, discontinuing it for a short time will not eliminate its effects on bile acids.