According ot everything I've been told the ideal time to give a bile acid test is about 16 weeks. Did your vet give you a pamphlet that explains your dog's blood work and that shows what the 'normal' ranges for each one is? According to the one I have from my vet the ALT normal range is from 18 to 50. I would ask your vet for a pamphlet and another explanation of the numbers. If you are still concerned or not sure I would seek a second opinion. You can also do a Protein C test rather than a sonogram...I've heard they are accurate and less expensive. Here is a Bichon website that explains your dog's blood work...
http://www.bichonfriseusa.com/caninebloodwork.htm