My vet just told me last week that if a liver is going into slow failure, the enzyme levels will not be elevated, depending on how much of the liver remains healthy.Only a full blood panel will tell you what state the liver is in - ALT, AST, ALK PHOS are the main numbers. There is a specific blood test to check the pancreas which you may want to consider. There are usually no symptoms at first and big thirst with weight loss are the first to usually appear.
Most liver issues are found in routine blood work for other reasons - annual, pre-surgery, etc. A dog I have never shows signs of liver issues; his enzymes just escalate to horrible levels and then we jump thru hoops to bring it all down. But nothing shows up on him physically or behaviorally. We just keep on tweaking diet and meds to keep him in the normal zone.
PS: dx was at 13 mths of age for pre-surgery bloodwork for neutering