Original post: Rapid Weight loss
How is the test performed?
The dog is fasted, blood is drawn, then the dog is fed a fatty meal. Two hours later, the blood is drawn again. The blood tests measure pre- and post- meal levels of bile acids, the acids stored by the gall bladder and secreted by the liver. If the levels are high, there may be a problem with the liver or hepatic vasculature.
What are bile acids used for, anyway?
When animals (humans included) eat, they need the bile along with other digestive elements secreted by the pancreas. The gall bladder, a bile storage unit, contracts to release bile into the small intestine as needed for digestion. From there, the bile acids do their work breaking down fats during the process of digestion. The bile acids are then absorbed by the intestine into the liver (portal) bloodstream and returned back to the liver. If the liver is functioning properly, the bile acids are removed from the bloodstream and returned to the gall bladder until they are needed again. This is called Enterohepatic Circulation, and is the body's way of "recycling" the bile acids.
What do the test results mean?
Comparing the two blood levels (pre and post meal) allows the veterinarian to see how well the liver, bile ducts, and blood flow to the liver are functioning. Bile acids are removed from liver (portal) blood by the liver cells (hepatocytes). If the liver cells are not functioning well, the bile acids remain in circulation and enter the body (systemic) blood supply where they elevated levels are measured by this test.
If post-meal (or even in some cases, fasting) blood levels of bile acids are high, this means that the liver isn't doing its job of removing the bile acids from the blood as it should. The actual numbers that are considered "normal" vary with the laboratory used, so please discuss numerical lab findings with your vet.