Dog - weight & muscle loss, high ALT index more than 1,000

Question
our 7yrs old mini-schnauzer has suffered from weight loss for 3 months, blood-tests showed high ALT (~300 in 18 Dec, ~600 in 10 Jan, ~1100 in 31 Jan) but all others are fine. ultra-sound results showed no abnormalities in liver and pancreas and other bowel organs. apparent muscle loss in body and forehead. urine test showed 2++ protein.
She was fed Royal Canin -Hepatic food as recommended by Vet.
still no exact diagnosis can be made.
She seems to get much more hungry than before during recent months.
faeces, drinking habit is normal, no diarrhea.

pls tell us what to do?  thanks.

Answer
Has your dog ever had a bile acids test?  Elevated liver enzymes show liver damage, but tell nothing about the function.  Bile acids test will determine if the function of the liver is compromised.  This is a fairly simple blood test.  A blood sample is taken, patient is fed a high protein diet, then another blood sample is taken 2 hours later.

I would also recommend an ACTH test evaluate for possible Cushing's disease.  This is a disease of the adrenal glands that produces too much cortisol.  Cushing's' disease can cause elevated liver enzymes.  This is also a fairly simple blood test.

I know you mentioned an abdominal ultrasound.  Was this performed by a specialist (a veterinary radiologist or internal medicine specialist)?  If not, I recommend having a consultation and an abdominal ultrasound by a specialist, who may also want to get a liver biopsy.  

Is your dog on a liver supplement called Marin, Denosyl, or Denamarin?  These are safe medications that dogs with liver disease routinely take. Ask your veterinarian about these medications and further testing.  Although testing can get expensive, it is the only way to get an accurate diagnosis.  Hope this helps.