<prompt> Signs and symptoms of a Renal Failure first appear when Renal function deteriorates by more than:20406080  <response>: Answer is C 60: Signs of renal failure become apparent when renal function deteriorates by more than 60 residual renal function between 20-50 while ove symptoms usually develop only after renal function has deteriorated by 75 - 80 residual renal function 20 