There are many causes for elevated ALT. With a level that high, I am really surprised your vet didn't discuss it with you. Since most causes are liver related, doing surgery ..well, if your vet put your dog under to clean its teeth after that number, you really need to get a consult with another vet or specialist.
Same here. After routine blood work to prep for teeth cleaning, my 7 year old male basenji has 900 level for ALT as well as high levels for ALK, Globulin, and Total Protein. We did an ultrasound as recommended by vet, which did not find anything abnormal in terms of enlarged liver or masses. Vet has suggested to start him on Denamarin, water soluble Vitamin E, and omega fatty acids. Then to test blood again in 1-2 months. Vet says to still go ahead with the teeth cleaning since liver issues can also be a result of teeth issues. Please let me know how it turned out for you!