You need to get Bile Acid Testing done on Griffin! Sure a liver shunt can be serious, but it also can be repaired surgically in most cases. Most liver shunt dogs also have IBD which it sounds like he could have.
Here is a great informative link:
https://vetmed.tennessee.edu/vmc/Sma...D-Brochure.pdf
And, here is a link about my Teddy Bear who was diagnosed with a shunt as an adult. He had blood work done over a period of 7 years and nothing was abnormal! So, regular blood work does not always show liver issues in a dog with a congenital shunt...it is dependent on the size of the shunt! It wasn't until he developed bladder stones that we found it. He had the surgery to repair it in 2013 and is fine now! The surgery really is surprisingly simple and they recover quickly!!
http://www.yorkietalk.com/forums/sic...ver-shunt.html