Bun @ 16 mg/dl creatinine 1.16 mg/dl estimated gfr = 49 1 kidney should i be concerned?

Low GFR, one kidney: You may hace chronic kidney disease (ckd). Your creatinine level is dependent is your age, sex, race and weight. You are the one to determine what those are. I would suggest you see a neprhologist and collect a 24 hour urine to see how well your one kidney is working. Another test that can be done is an ultrasound of your one kidney to see its size and to see if there is any presence of ckd.