Protein C is a blood test that is sent to Cornell; here are 2 links about it:
http://www.diaglab.vet.cornell.edu/c...t/proteinC.asp http://www.vin.com/proceedings/Proce...2675&O=Generic
(see under Liver function test toward the end of paragraph)
Is your dog having symptoms associated with liver disease, or did you just discover it thru routine bloodwork (like I did)?
Good luck, and do keep us posted.