Dear Giants,
The very same thing happened to me. And Sherri's comments are spot on. I was trying to exercise seriously, to keep my BP and weight down for final approval, and I ended up dumping protein into my urine as a result (in retrospect, I'm also not sure that eating several [high-protein] tofu sandwiches in the days before my test was a great idea). The medical director of the transplant program, a nephrologist, was not amused, and was ready to cancel my donation (I'd been in the process for nearly a year by then!) I refused to take no for an answer, and ended up getting another 3 or 4 24-hr. urine collection tests, with no exercising, and I did fine. However, the brief period when I thought I would not be approved was truly awful.
Still, even as I was shouting at her that she couldn't throw me out, I respected the nephrologist for looking out for me. Even though I sort of viewed her as my "enemy" at that stage, the fact that she "had my back" (rather than being a vulture just dying to grab my kidney) allowed me to demand to continue. I figured that if it really was unsafe (I mean, I'm not nuts), she just wouldn't let me do it.
In the end, everything has worked out so far for my donor and I, nearly 7 months post-donation. I hope things work out for you. Keep us posted.
Be well, Snoopy