My 9 month old son has 82% efficent kedney on left & 18% on right, what may be consequences?

Depends on pbm: Your ? Does not list the origin of the problem. Loss of fcn can be attributed to structure/blockage/infection/ metabolism. Any or all may have differing outcomes. A top question in my mind is the potential for hypertension from changes in the weak kidney & or progressive loss of function.Close followup with your physician and a frank discussion of the future surveylance needs are in order.

More information: It would be very hard to analyze this problem without any medical history and the underlying cause of the poor renal function in the R kidney. I suggest you see a pediatric nephrologist to get more answers on outcomes. It may be necessary to have some specific renal function tests done to get a good answer in this case -that could involve surgery as well as special nuclear medicine studies.