Bile Acid Testing

Liver enzymes (ALT, AST, LDH, ALKP and GGT) help identify damage to
liver cells and serve as indicators of hepatocellular integrity or
cholestasis, whereas bile acids are an indicator of liver function,
despite the presence or absence of hepatocellular injury.

by Michelle Kahn, MS, DVM

Bile Acids Basics:

There are many reasons the bile acids test has become the liver-
function test of choice in the veterinary community. It is relatively
inexpensive and easy to perform (all that is required is a fasted
serum sample and a two-hour postprandial sample), and best of all,
it is a very sensitive indicator of liver function. To obtain the
best results, there are some basics to consider when performing
this assay:

A 12-hour fast must be undertaken prior to the first (preprandial)
sample.

It is very important to perform a postprandial sample, as well as
a fasting sample, or the diagnosis may be missed.

The amount and type of food used with this assay are important.
While the amount of food is not known for sure, general recommendat-
ions are to feed at least 2 teaspoons of food to animals that weigh
less than 5 kg, and approximately 1/4 can of food for larger animals.

You don't want to overfeed because lipemia can adversely affect the
bile acids results, and you should avoid foods with low-fat and low
protein concentrations.

Hemolysis can adversely affect your test results. Careful sample
handling and a large-gauge needle are useful to avoid hemolysis,
which can significantly impact bile acids assay results. If you
note hemolysis, you should draw a new sample for testing.

Sometimes, preprandial levels may be higher than postprandial levels.
This may be due to many things, including delayed gastric emptying
and interdigestive gall bladder contraction.  It is suggested that
you retest if this type of result is noted. You should also consider
that owner compliance might be a problem and the client may have
tried to sneak some breakfast to the dog. It is important to emphasize
that the patient must be fasted for the retest!

The Maltese conundrum: abnormal bile acids test results are commonl
seen in this breed when there is no liver function abnormality.
This is obviously a concern since this breed is genetically pre-
disposed to portosystemic shunts (PSS). Therefore, an abnormal
bile acids test result is inconclusive, but a normal bile acids
test can rule out PSS in Maltese puppies. Several other terrier
breeds may also produce suspect results.

Don't test icteric "yellow" dogs. Knowing when not to run can be just as
important as knowing when to run the bile acids assay. If an animal
is icteric (and not anemic), there is no reason to run a bile acids assay.
You already know that liver function is compromised in this patient, and
you should move on to finding the cause of the liver disease.

To get the most out of your bile acids testing, you should keep in mind
that a complete diagnostic workup is essential to diagnosing liver
disease in the cat and dog. You should always perform a complete CBC,
a biochemical profile and a urinalysis (including a sediment exam)
prior to evaluating liver function. I can think of several cases
where I went back and tested for a portosystemic shunt after noting
ammonium biurate crystals in the urine. Even though there were no
clinical signs and nothing in the history suggested a shunt, it
was present. If possible, you should assess the liver with diagnostic
imaging as well. An ultrasound can be particularly beneficial,
especially in the right hands. The more complete your diagnostic
protocol, the better your chance of discovering the underlying
pathology and successfully treating your patient.

To contact Dr. Kahn, e-mail   Didyouknow@idexx.com     
(The above elicited from:
http://www.idexx.com/animalhealth/analyzers/vetlabnotes/2005snapreader.jsp   )