[kjc]

It's not unusual for most hospitals to want to do their own tests. As they are more specialized, this would make sense, as many regular vets are not as familiar with specific test protocols and procedures.
One can see a shunt with an ultrasound, but they have to be very experienced to do it successfully. Usually, once the BAT is done by the regular vet, most are referred to vets/hospitals that specialize in liver disorders.