WC rules differ by state. The result of how refusing a diagnostic test will differ greatly based upon many factors. In CA, your primary care doc absolutely has the power to change your status from TTD to P&S, for ANY reason. This can mean an end of income, but it can also put the breaks on moving forward with potential treatment, and/or receiving medications. Many states have very strict rules in place that prevents the injured worker from switching docs. (In part, so that the IW can't doc swap when they're status is changed to P&S.)

If the OP can avoid (or postpone) the test, that is clearly preferred. But, the only person she should trust that it won't effect her WC case, would be her attorney (if she has one.)

In my case, it wasn't my primary, but an IWE. Once agreed upon ahead of time by both parties, you're stuck with them. If I had experienced past episodes of spread from similar procedures, I would have refused. Since I've had no long term pain other than the original RSD site, I was not too worried. My flares have responded quite well to meds. I had a plan in place with my PC, if the worst case scenario happened. Etc. Was it a difficult decision that required significant consideration? Of course.