I'm sorry.
Liver shunt can't be diagnosed with bile acid testing alone. Diagnostic imaging would be done before opening him up. Microvascular dysplasia is possible. That is like microscopic shunting throughout the liver and is not surgical but manageable medically. You boy needs to see an internal medicine specialist at a major specialty center or vet school for future assessment. The surgery is risky but not terribly so if done by the right people on an otherwise stable pup.