your bros nephrology team will help u trust me, ur creatine is only slightly elevated, get your urine checked for protein, good luck
if your concerned forget your doc waste of time, your brother must be under the care of a nephrologist ask him hell know better than a gp who knows just a little about everything, im a renal patient, and i know that on kidney is sufficient to live but youve only got 50 percent function now, understand youve got 100 percent of 1 kidney meaning 50 percent function so creatinine can sometimes be expected to be high same as your bro, whats his creatinine,
ps, what a great person u are donating a kidney, a credit to you. im sure god will give u a long healthy life.