Bile acids measurement is a highly sensitive assay to assess hepatobiliary function. Bile acids are derived from cholesterol in the liver, released into the intestine after eating to aid in fat absorption, then enter the portal circulation to be cleared by the liver and re-excreted into bile. Serum bile acids concentrations may be elevated in diseased states leading to decreased functional liver mass, with obstructive cholestasis, and with congenital or acquired portosystemic vascular shunts. This test does not differentiate these underlying types of liver disease.
While biochemical changes including elevated ALT, AST, ALK, bilirubin with decreased albumin, urea, glucose, and cholesterol, and prolonged coagulation times may suggest liver failure, these analytes may be in normal reference interval with various liver conditions or be altered by non-hepatic diseases. They are not reliable primary indicators of liver function compared to bile acids measurement.
A bile acids “challenge” test with both a pre- and two-hour post-prandial blood collection is recommended over a single fasting or random sample (in dogs and cats) because it has substantially higher sensitivity for detecting disease. Feeding stimulates gall bladder contraction and the release of bile acids into the intestine and eventual portal circulation. This increased load can better “challenge” the liver’s ability to clear the increased bile acids presented to it.
Indications for testing
- Bile acids challenge testing should be performed when there are clinical and biochemical findings that suggest liver dysfunction or portosystemic shunting.
- Testing is NOT indicated if the patient is icteric from hepatic or post-hepatic cholestasis, as bile acids will inevitably be high and not provide additional information. In patients with pre-hepatic icterus (haemolysis), a bile acids challenge test can help rule out hepatic aetiology, if not readily apparent.
- When used as a screening test in puppies from breeds that are predisposed to congenital portosystemic shunts, it is recommended to delay testing until after 16 weeks of age, as bile acid concentrations may be falsely lower in puppies younger than 16 weeks.
Test Protocol:
Sample haemolysis and lipemia can interfere with bile acids measurement and should be avoided by fasting, using a large gauge needle, jugular venepuncture, and separation of the serum after clotting.
1. Collect the fasting sample:
- Fast the patient for 12 hours.
- Collect the first blood sample, and label the tube with patient name and “0 hr” .
2. Feed a small amount (2-4 tablespoons) of canned maintenance-type diet. Note that a high-fat diet is NOT necessary, and can sometimes contribute to unwanted sample lipemia if given in excess.
3. Collect the post-prandial sample.
- Two hours after feeding, collect the second sample and label with patient name and “2 hr”. Submit both tubes to Gribbles with the completed request form.
Interpretation of bile acids challenge test:
Using Gribbles reference intervals, post-prandial bile acid concentrations >31 umol/L (dogs) are suggestive of hepatobiliary disease (decreased functional mass, cholestasis or portovascular shunting). Values between 15-31 are equivocal, and such dogs may or may not have liver dysfunction. Most animals with congenital or acquired portosystemic shunting have markedly increased post-prandial bile acids concentrations.
Up to 20% of the time, the fasting bile acids may be higher than the post-feeding concentration. This can be due to a recent meal before testing, spontaneous gall bladder contraction, insufficient gall bladder contraction after feeding, or variations in gastric emptying, intestinal transit time or absorption. If both results are <31 umol/L (especially <15 umol/L), then hepatobiliary dysfunction is unlikely.
Maltese dogs – Update!
Gribbles has previously reported that bile acids measurement in the Maltese breed may have questionable utility, based on a 1995 Australian study (Tisdall et al, Aust Vet J) which found that this breed may have “artifactually” elevated serum bile acids caused by unknown reacting substances. In this study of 200 Maltese dogs, only 11 dogs had liver biopsies performed. More recent research presented by Sharon Center (Cornell University) at the 2012 ACVIM Conference refutes this supposition, based on genetic mapping work and liver biopsies from Maltese dogs. Center has found that Maltese often have portal hypoperfusion. In evaluation of 136 liver biopsies from Maltese dogs, 22% had congenital “classic” portosystemic vascular anomaly (PSVA) whilst about 60% had microvascular dysplasia (MVD) without PSVA. Every Maltese with portal hypoperfusion had high serum bile acids concentrations. In most of those cases, the presence of increased serum ALT in conjunction with high bile acids initiated the collection of a liver biopsy. With these recent findings, Gribbles confidently endorses the use of bile acids “challenge” test in Maltese dogs, as for other breeds. While ammonia tolerance testing remains an alternative test to assess liver function, ammonia measurement is problematic, inconvenient and very unstable.
Species:
Dog, Cat
Specimen:
Serum (minimum 1 ml)
Container:
Plain tube, gel tube
References:
Center SA. Breed-Specific Hepatopathies: Scottish Terriers and Maltese Dogs. ACVIM Proceedings 2012.
Cornell University Veterinary School website. Bile Acids. https://ahdc.vet.cornell.edu/clinpath/modules/chem/bileacid.htm (visited 21/05/13)
Shell, Linda et al for VIN community. Bile Acids, Medical FAQs 18290418, last updated 01/11/08.
Stockham SL and Scott MA, 2008. Liver Function. In Fundamentals of Veterinary Clinical Pathology, 2nd ed., Ames, IA: Blackwell Publishing, pp. 675-706.
Tisdall PL, Hunt GB, et al. Post-prandial serum bile acid concentrations and ammonia tolerance in Maltese dogs with and without hepatic vascular anomalies. Aust Vet J. 1995;72(4):121-6.