Hi, I am not on 6 mp yet but know from my daughter who had leukemia and was on 6mp for 3 years that everyone metabolizes this drug differently. There is a prometheus test that can check your TPMT level which can tell you if you are an average, below average or above average metabolizer of the 6mp. I just got my results yesterday and it says I am way below normal at 21.0 so they are starting me on azithopan(spelling??) like 6mp but 50% of dose. He thinks 6mp will bottom me out. My GI likes to see the wbc between 3.0-4.0. Again, from my daughter's experience when you get a cold whether it is viral or bacterial it can either lower your wbc or higher it. That is a good time to get the wbc checked. There is also a drug called GCSF if the wbc gets too low for too long and you need to recover. Probably much more info than you needed but finally something I know since I am a crohns newbie!!
I was just worked up for a low white cell count, specifically the neutrophils. My situation is a little different in that I'm not taking a drug known to lower the WBC like 6-MP but it is still a low WBC, with the same risks, i.e. the inability to fight infection.
The hematologist I saw said that my WBC, which just dropped from 30 years at 3-3.6 down to 2.2 was not too concerning. I had asked him about treatment with methotrexate which had been considered at one time and he said it would require dosing considerations and extra monitoring but it was not ruled out, even with a WBC this low starting the treatment. So, even though a normal WBC ranges from 4-11,000 it can go considerably lower before there are serious concerns. Even at a level of 2.2 I don't have a problem with infections