In response to your question regarding imuran and special testing, my GI says Imuran is for the long term(versus prednisone) at least for me.The special test is most likely Prometheus and it measures how your liver enzymes process the drug, specifically how much of that liver enzyme you have which determines how much Imuran your body can process and then help you heal. For me, I probably can't take more than 50/mg of Imuran a day as I don't have a lot of this liver enzyme and then my white blood cell count would go haywire, which would be all sorts of badness apparently.
For the record, I do like Imuran as well, it has helped me a whole lot with this flare, though I still can't get off pred, and will be starting remicade soon :(
Hope this helps!!