Cirrhosis can be quantified by liver biopsy as well as biochemical markers like
platelets, bilirubin, albumin, INR
and others. Also to some extent through imaging; U/S scan, for instance can determine organ dimensions, portal vein diameter, proper flow through the portal tract, etc.
As far as expressing the damage, of course they use the terms ‘compensated’ and ‘decompensated’. This can also be expressed by the Child-Turcotte-Pugh scale:
http://en.wikipedia.