Fifty Shades of Bile Acids

Date added: 9th June 2015

 
The following extract is taken from the information provided by Simon Tappin, European and RCVS Recognised Specialist in Veterinary Internal Medicine, in Session 1 of the ‘Liver and Pancreatic Disease’ online Mini Series

There are lots of things we can look at that give us an idea of liver function, but perhaps the best available test is to look at bile acids. Even so, bile acids aren’t the most specific test to tell us exactly what is happening with the liver and have to be interpreted to some degree. There are lots of ‘shades of grey’ when it comes to liver disease when we are looking at blood results, and none more so than when we are thinking about the evaluation of bile acids.

Essentially, the bile acids are produced in the liver, stored in the gall bladder, and excreted into the gut. They help to emulsify fat and about 90% are reabsorbed from the ileum. About 60-70% are taken out in the first parts of metabolism as they come back through the portal circulation, so they can be reused and excreted again into the gut to help digest more fat. So it helps us to look at the excretion and then the resorption; the filtering of the bile acids as they come back through the liver.

Bile acids are a robust analyte – they don’t degrade over time. We can send samples in the post really easily. We tend to measure them as a baseline and then 2 hours after feeding. So, we give a fatty meal. We try to release as many of the bile acids from the gall bladder as possible, which occurs because of cholecystokinin release from the stomach in response to the fatty meal. The gall bladder contracts, and we can then measure how many of the bile acids have been filtered out from the bloodstream by the liver 2 hours later.

We can get some unusual results sometimes. We can get spontaneous gall bladder emptying in animals which are nervous for example, giving spuriously high results. Sometimes we don’t get good stimulation of gall bladder emptying by feeding, and experimentally we can inject cholecystokinin to make sure that happens, although clinically this is not currently done in the UK.

Generally, we have a cut off of about 25-30µmol/l for some indication that there is hepatic dysfunction in dogs and cats. Some laboratories have reference ranges which are much lower. We don’t tend to get excited about bile acids until post-prandially they are over that level, and even then they are not starting to get specific for liver disease until reaching values of 50 or 60µmol/l. Bile acids are interpreted as a ‘shade of grey’ rather than an absolute value that definitely indicates liver disease at that point. Values >100µmol/l are starting to get suggestive of portosystemic shunts – blood missing out the liver and ending up in the general circulation. We do see some dogs who have portosystemic shunts that have values lower than that however, and others that are much, much higher.

Therefore bile acids have to interpreted in the context of the clinical case.

 

You can discover more about how to approach liver disease in dogs and cats by registering for the Liver and Pancreatic Disease Mini Series with Internal Medicine Specialist Simon Tappin. Following purchase, you will get immediate access to this online course for 12 months!