Bile acid tests should really be done at or after 10 weeks of age.
The breeder should keep this pup until its old enough for the test. If you do it at 8 weeks and its high you will have to repeat it again in a month or so.
You probably won't get the results in 48 hours either.
You should ask the breeder to hold the pup until its old enough to test and have her do the test before placing it with you. If they don't want to pay for it you can, but it should be done by the breeder.
Of course this is JMO.
It is considered genetic and you should have a guarantee against it.