Renal function tests are very common, and done to measure how well an individuals kidneys are working. Some common types of renal function tests are the BUN test, creatinine blood test, creatinine urine test and creatinine clearance test, according to Medline Plus.
Creatinine is a natural product that occurs in the body as muscles change over time. It is also a waste product that occurs due to animal protein in the diet. High levels indicate that the kidneys may not be functioning properly. Normal BUN levels are between 7 to 20 milligrams per deciliter. When BUN levels are higher, this indicates kidney function is decreasing, according to WebMD.