if the dr is aware of the kidney problems them everything should be ok. But here is a little info I was able to find on the subject:
Kidney, heart, or other problems that require medical tests or examinations that use certain medicines called contrast agents, with x-rays—Metformin should be stopped before medical exams or diagnostic tests that might cause less urine output than usual. Passing unusually low amounts of urine may increase the chance of a build-up of metformin and unwanted effects. Metformin may be restarted 48 hours after the exams or tests if kidney function is tested and found to be normal
Hope this helps you. | 
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