by John Dillberger, DVM
The liver produces bile acids and secretes them into bile, which is stored in the gallbladder. When the dog eats a meal and the food begins to leave the stomach and enter the small intestine, the gallbladder expels some bile into the upper small intestine, where it mixes with the food. The bile acids help dissolve fats and fat soluble vitamins so they can be absorbed. The bile acids are absorbed, too.
Everything that is absorbed from the intestine (nutrients, bile acids, toxins, etc.) is carried first to the liver. (This part of the circulatory system is called the portal circulation.) There the blood must percolate through the liver as if it were a sponge before it can reach the part of the circulatory system that supplies the rest of the body (called the systemic circulation). During that percolation process, the liver gets first crack at nutrients and also has a chance to remove anything undesirable, like toxins. The liver also gets a chance to recapture bile acids, which it does. Thus, the same bile acids can be used over and over again—very efficient, and takes a lot less energy than making new bile acids all the time. Of course, the liver is not 100% efficient at recapturing bile acids, so some make it through and into the systemic circulation. Thus, there is always a low level of bile acids in the blood.
A liver (or portosystemic) shunt connects a blood vessel in the portal circulation with a vessel in the systemic circulation, so that blood can pass directly from one to the other without percolating through the liver. All puppies have shunts in the womb, because the liver of the fetal puppy does not need to cleanse the blood as the puppy’s blood is being cleansed by the mother’s liver. The shunt is supposed to close soon after birth, but in puppies diagnosed with a shunt, the shunt doesn’t close. Sometimes there is single connection, and sometimes there are many. Sometimes the connection bypasses the liver entirely and sometimes it just shortens the percolation path. In any event, you can imagine what that would mean. Blood (and all it contains) can pass from the small intestine into the systemic circulation with less-than-the usual filtration or with no filtration at all.
In the first situation (reduced filtration), the liver may be able to handle everything between meals, but not the load of substances that arrives after a meal, and so some of those substances (including bile acids) will escape into the systemic circulation. As a result, bile acid levels in the systemic circulation may be normal except after a meal, when they will rise. The rationale behind the bile acid test protocol is to look for this rise.
In the second situation (no filtration), bile acid levels typically are high all the time, even between meals, and can rise to very high levels after a meal.
More information on liver shunts and bile acid testing can be found here:
This is the Texas A&M Veterinary protocol for liver shunt testing; if you are using the Texas A&M lab, please give this to your vet. Most labs will be similar to this, but contact your vet for specific instructions if you are using another lab:
- • Withhold food from the dog being tested for at least 8 hours.
• Collect a baseline 3mL blood sample from a peripheral vein and place in a serum tube (red top without the serum separator plug) and label the tube “fasted” along with the dog’s ID.
• Feed approximately three tablespoons of canned dog food such as Hills p/d.
• Two hours later collect a 2nd 3mL blood sample from a peripheral vein and place in a serum tube (red top without the serum separator plug) and label the tube “2-hour” along with the dog’s ID.
• Allow each sample to clot for at least 15 minutes, and centrifuge no longer than 30 minutes after the blood is collected.
• Harvest the serum and place in a plastic tube suitable for transport.
• Each plastic tube should be labeled “fasted” and “2-hour” as appropriate, along with the dog’s ID.
• The serum samples should be stored at -20 degrees C, and shipped to the GI Laboratory at Texas A&M University.
Complete the Texas A&M University GI Lab Submission form prior to shipping.
Some folks will first screen for a shunt by taking only a post-prandial (the sample taken two hours after feeding) blood sample. Whether you use only the one test or do the full protocol, for any results that come out high, or even equivocal, it is recommended that you retest using the full protocol with samples taken both after fasting and two hours after feeding.
As for age at which to test, one usually waits until the pups are weaned and eating on their own and can manage a short fast (say, 6 to 8 hours). For small breeds, one also waits until they are big enough to get a couple of blood samples, but that is not an issue with Deerhounds.
Many labs do bile acid testing, so you can use any lab that runs the test unless you want to get CHIC numbers (not to be confused with our CHIC DNA bank — they are two completely separate things) on your dogs. If you want to get CHIC numbers, bile-acid test results from IDEXX, Antech, and veterinary college laboratories will be accepted. Please note that only tests done by one of these laboratories will be accepted. Results from in-house testing done at private veterinary clinics, even if run using equipment and/or kits from IDEXX, will not be accepted.