I would skip the ultrasound. According to Dr. Center, they can be as low as 60% accurate. Save your money.
Since the cut off is less than 25, his bile acids are abnormal but not terribly high. Bile acids over 100 are usually indicative of a shunt, but head wobbling and disorientation are classic signs of a shunt.
I would go ahead and get a Protein C test done.
Comparative Coagulation -- NYS Animal Health Diagnostic Center