Each transplant center determines the guidelines that they will use to accept someone as a kidney donor. There are no national or international guidelines that are universally recognized. I can only suggest that you seek a second opinion at another transplant center, if you wish to be re-considered. The levels of kidney function that you quote seem to be pretty good, but each transplant center determines the criteria and they have the option of refusing you as a donor, if you do not meet their criteria.
For more information on living donation click here: