Kidney function can be evaluated by measuring substances in the blood that are filtered and excreted by the kidneys. Elevations in these substances may indicate inadequate cleansing and filtering of the blood by the kidneys. Examples of this are two substances called creatinine and blood urea nitrogen, or BUN. Both BUN and creatinine are by-products of our normal metabolism. Small amounts are typically excreted in the urine. Of the two substances, creatinine is a more specific indicator of kidney function.

If the kidneys are not filtering well, perhaps as the result of untreated hypertension, the creatinine level in the blood will be higher than normal. This will influence the type of medication that your health care provider chooses to control the high blood pressure. The BUN may indicate kidney damage as well, but there are other reasons why a BUN level might be elevated. Remember, many people have more than one disease process occurring at the same time.