Bile is needed for digestion, so when you eat food...bile is released into the intestines and then the bile acids are absorbed by by the intestine into the portal blood and returned to the liver. Bile acids are removed from the portal blood by liver cells. If the liver cells aren't working properly, bile acids are not removed and enter the body's blood supply. This is what the bile acid test measures...
Here's a good article:
http://209.85.165.104/search?q=cache...lnk&cd=2&gl=us