Try not to panic. Bile acids test results can be skewed if the test is not done correctly. Dr. Center, the developer of the bile acid test, recommends that Yorkies be tested at 16 weeks and again at six months. Since the numbers were relatively low, you might want to just wait and retest in another month.
There is lots of information on bile acid testing on the YTCA website including the proper protocol for the testing.
Health Committee
Here are some other good links for you:
PSVA and MVD Research Summary Portosystemic Shunts FAQ
I agree with Nancy 100%. You should contact his breeder and let her know the results.