Normal levels of blood urea nitrogen, or BUN, for adults and children range from 10 to 20 and 5 to 18 milligrams per deciliter, respectively, according to WebMD. For adult men and women, normal creatinine levels range between 0.7 to 1.3 and 0.6 to 1.1 milligrams per deciliter, respectively, according to Healthline.
A BUN test measures the amount of nitrogen released from the waste product urea into the blood, explains WebMD. Since the kidneys are responsible for removing urea from the blood, changes in the blood urea nitrogen levels usually indicate that the kidneys have a disorder. However, dehydration, heart failure and a high-protein diet may also cause high BUN levels, while liver disorders and a normal pregnancy in its second or third trimester also lower BUN levels. Doctors test for BUN to check for normal kidney function, to check on the progress of a kidney disease, to see whether a treatment is working and to check for severe dehydration in patients.
A creatinine blood test measures the amount of creatinine in the blood, explains Healthline. Creatinine is a waste product formed when creatine breaks down. The kidneys remove creatinine through the urine, and any disorders cause a rise in creatinine levels, as the kidneys are unable to function properly. Doctors test creatinine levels to check on the function of the kidneys and diagnose other conditions, such as diabetes.