Stage II renal failure

I have an extensive history of kidney stones with numerous lithotripsies (8+) done and one percutaneous nephrolithotomy.  I am wondering if this could have contributed to the diagnosis of Stage II renal failure (I understand that this is mild).  If not, are there any specific causes for this condition?  I take a diuretic when it is necessary because I do have some edema problems and I am on a low dose ace inhibitor to take the strain off of the renal artery.  I am undergoing chemotherapy for breast cancer at this time and am scheduled to receive the CAT regimen.  I have already completed the CA part.  My nephrologist did some follow-up labs and was pleased with the results, which indicated that the chemo was not having any adverse effect on my kidney function (good because I am being treated aggressively for an aggressive form of breast cancer).  I am concerned about one thing....on the next set of labs, she has ordered a magnesium level and listed among the ICD 9 codes a "disorder of magnesium metabolism".  Is this something I should be concerned about?  Any  information you can give me would be greatly appreciated.