Blood and urine tests are used to determine your kidney function. Routine blood tests used are Blood Urea Nitrogen (BUN) and Creatinine. These levels show your kidneys' ability to remove blood toxins and, in general, the higher these numbers, the lower your kidney function. GFR (glomerular filtration rate) is also typically included in routine blood tests. It’s not directly measured but calculated based on your creatinine level, age, sex, and other factors. In general, a lower GFR indicates reduced kidney function.