Question

I have a 5 year old beagle. She has allergies and gets injections for them. She also bites on her feet constantly and drags her butt. Last year they took a blood test to check her liver count, it was 800 and last week it was taken again it was 1200. She act a feels fine. She is overweight 35 pds. She does not have accidents in house and has always drank water often but I think its because she likes poland springs water and its cold. Her poop tends to have a membrane texture and at time has streaks of blood (that I'm guessing is from always dragging her butt) My vet wants me to get an ultra sound done to see her liver. Is this extreme? Again she is playful and no loss of appetite. I was woundering if there is other actions we can take before doing the ultra sound