Hi. My Tinkerbelle goes in tonight for her liver enzymes recheck- after her 1st moth of meds: AB 2xD, Lactulose 2XD, and Denamarin 1XD. The AB's kill the bacteria in the intestine to stop them from producing amonia, the Denimarin is combo Sam-e and milk thistle that help repair liver cells and prevent damage to them, and the Lactulose changes the pH of the intestine and helps move the byproducts out quickly so the intestines absorb less, giving the liver less to do. Initially her ALT was 433.
I think most tests won't tell you which problem your dog has. The higher dollar tests will. Even if LS is detected, MVD can still be present. I don't think surgery is an option for older dogs. Most cases are medically/nutritionally managed anyway.
Check out
www.livershunt.com they give a good diet for dogs with liver problems.
Goodluck.