I was diagnosed in February of this year
and was given a prescription for
Avonex that day. I had to have a blood test to check my
liver function and my AST and ALT levels were way high, and to make a long story short, they still haven't come back down to "normal" and I'm still not on Avonex.
Apparently, liver function tests have to be done every 3 months for the first year on Avonex (or any interferon, for that matter), and they recommend 6 to 12 month intervals after that.