Dr. Center has recently revised her protocol for bile acid testing from sixteen to eighteen weeks being the youngest age to have it done. She has found that the organs just aren't developed enough before 18 weeks and false negatives are possible.
Bile acids tests are perfectly safe, just a simple blood draw. The danger is in
NOT getting one done.
This new article by Dr. Center (June 2008) is a must read for all Yorkie owners.
http://www.yorkiefoundation.org/purina1.pdf