Natalie,
Sorry to hear you are going through this!
My advice about your Tysabri infusion is the same as everyone else's. Tell the nurses what you have been through and the results. Have your doc fax the results over. The infusion center will talk to your neuro and he will have the final say.
Don't take chances with your health for your infusion. You can have it later if nothing is wrong. Get whatever is going on diagnosed and cleared up. It may be neurogenic bladder. It may be something else entirely. Figure out what it is and don't worry about being a few days late on the infusion. Worry about your kidneys first.
Peeing is a BIG DEAL!