1. The bile-acid test is a diagnostic test that only requires two blood draws from a dog. So the test is very safe for the dog. The test is not terribly expensive.
2. In the population of dogs seen at the UC-Davis Vet Hospital from 1995-2010, Norwich terriers were the second most likely breed to have a liver shunt (after Yorkies). (Source: article in the June 2013 JAVMA.)
3. Instead of liver shunts, a dog can have Portal Vein Hypoplasia, sometimes called Microvascular Dysplasia (PVH-MVD), which is suspected of being a genetically related (but milder) form of a liver shunt. The incidence of PVH-MVD is higher than liver shunts.
4. Dr. Sharon Center, an expert in canine liver shunts, recommends that bile-acid testing should be done in all young puppies of predisposed breeds for future health care considerations; discovery of high bile-acid concentrations during an illness may lead to inappropriate, invasive, and expensive diagnostic testing. (Source: Merck Vet Manual, article reviewed May 2015 by Dr. Center)
You do not want a vet to surprisingly find high bile acids when a dog is presented for an illness. This can result in testing that may include an expensive abdominal ultrasound and even a liver biopsy in a dog with PVH-MVD - consider for example a dog presented for vomiting after eating garbage. A high bile acid test would implicate the liver as being severely affected, and the vet would be obligated to inform the client that the liver should be investigated. If they already knew the dog had high bile acids as a pup, consistent with PVH-MVD, then the medical investigations would be judiciously focused on the vomiting.
For more about liver shunts and bile-acid testing, see liver shunts