Current methods to assess kidney function have not been tested in people who have HIV/AIDS population. Given effects of the disease as well as potential effects of the medications, it is possible that the methods currently used to assess kidney function are not accurate. This purpose of this study is to evaluate methods to assess kidney function the HIV population. The investigators hypothesize that tenofovir causes a decrease in the secretion of creatinine which would cause an elevation in blood levels without affecting actual glomerular filtration rate (GFR).