Liver values, especially ALT, in ferrets can be thrown off badly by not
eating enough or by not eating often enough.  If you go to
http://www.afip.org/ferrets/index.html
 
and open
 
Confusion and Controversy in Interpreting Ferret Clinical Pathology Data
http://www.afip.org/ferrets/Clin_Path/ClinPath.html
 
then scroll down you will find the info in the section which begins:
 
>Probably the most common misinterpretation that I see on a routine basis
>is in the area of hepatic enzymes.  Remember, that the ferret, being by
>nature an obligate carnivore, has an extremely short digestive tract,
>and requires meals as often as every four to six hours.  Should food not
>be available, it possesses the ability to quickly mobilize peripheral
>fat stores in order to meet energy requirements.  When this physiologic
>mechanism is activated, the liver is literally flooded with fat, which
>results in hepatocellular swelling which may be marked.  The result
>of this swelling is the leakage of membrane enzymes such as alanine
>aminotransferase, and as the hepatocellular swelling increases,
>occlusion of bile canaliculi occurs, resulting, over time, in elevation
>of alkaline phosphatase.
>
>In conjunction with this physiologic change, elevations of ALT up to
>800 mg/dl can be seen, and alkaline phosphatase up to approximately
>100 mg/dl.  This often causes confusion to practitioners, who render
>an erroneous diagnosis of unspecified hepatic disease...
 
There is much more for you there!
[Posted in FML issue 4463]