This link is for the Univ of Tenn and will tell you everything you ever need to know about Liver Shunts.
Portosystemic Shunts FAQ
My dog BAT tested at 126. She is eating L/D (low protein) and takes liver support meds. I asked my vet to do an x-ray first to determine the size of her liver and to see if any gallblader problems were evident. (I am cheap and this was the cheapest thing to do, and gives you some insight as to what you're dealing with.) Gallbladder problems can skew the BAT results.
We also did bloodwork, to check the liver enzymes and chemistries... normally done before the BAT, but if it wasn't, you could do it now.
Because her BAT is 126, my dog most likely has a shunt, just on that number alone. As no GB problems evident on xray, her liver is small, next we're going to do an Ultrasound, only bc my vet is confident that her u/s person can do it well enough to find a shunt. I had planned to go to U of T, but as her BAT could be alot higher, I'm thinking maybe she has MVD (bad case) and I didn't want to waste a trip if she ends up with MVD or multiple shunts, as they are not operable. If she appears to have a single shunt, we'll be going to U of T for a scintigraphy and surgery there as they are the most experienced and the least expensive.
Since diagnosis, she has been on a low protein diet and medications (Denamarin and Lactulose) and is doing well.
Because so many BATs have been done, normally any result over 100 means there's a shunt. Any result less than 100 means they have MVD.
If your dog was mine, I would put her on Hill's Prescription L/D diet, and redo the BAT in 30-60 days, provided she shows no symptoms. If she shows symptoms, then I would start her on Denamarin (liver support) and Lactulose.
If her next BAT is less, I would accept that she has MVD and keep her on low protein for life. If it increases, maybe do an ultasound if your vet knows a good one, or go to U of T for further testing.
Read the info on the website, it will help you to understand alot.