Some people can't metabolize Imuran and it builds up in your liver. there is a fairly easy blood test they can run before a person starts the medication that can determine if you have a genetic mutation to the enzyme thiopurine
S-methyltransferase (TPMT) that metabolizes thiopurines. If you have poor metabolism, the Imuran builds up and becomes toxic and can be very serious. There is a simple blood test that determines if you have the defective gene. They should do the blood test before starting the medication...in my case they didn't. I'm off the Imuran and started CellCept a year and a half ago. i don't think it is working
Here is a link that might explain the TPMT enzyme better.
http://www.specialtylabs.com/educati...DF/TN_1196.pdf