My girlfriend donated a kidney to her mum a year ago. now she was diagnosed with a stage 3 renal impairment. will she need a transplant?

Probably not : All people living with one kidney instead of two have less function than they used to. A donor is predicted to have about 75% of their pre-donation function. We generally require a GFR of >80 to donate, which means that stage 3 (45-60) is a bit lower than we would like to see. It is important to keep her weight, BP and glucose in control, and to see a kidney doctor regularly for protection.

Transplant?: At her stage, 3, of chronic kidney disease (ckd), she has sufficient renal function to allow her to live off of hemodialysis. The question should be to the doctor who diagnosed her with class 3 ckd. You should have her return to him to see what the cause of her CKD is. She had a rapid decline in her kidney function, as i suspect she had no CKD one year ago. See a nephrologist and find out why.