Test/Monitor Kidney Function

The purpose of the kidneys is to remove wastes and excess fluid from the blood.  Tests exist to check whether the kidneys are working properly: Blood tests can indicate whether the kidneys are failing to remove wastes; urine tests can show how quickly bodily wastes are being removed, and whether the kidneys are leaking abnormal amounts of protein.

Function

Blood and urine tests are key to monitoring kidney function.  By seeing which waste products are remaining in the blood, and which are being expelled via the urine, diagnosticians can determine whether the kidneys are functioning properly.

Serum creatinine. Creatinine is a waste product that comes from the metabolizing of meat protein in the diet, and from the normal wear and tear on muscles of the body.  Higher levels may be a sign that the kidneys are not working properly.  As kidney disease progresses, the level of creatinine in the blood increases.

Blood urea nitrogen (BUN). Urea nitrogen also results from the breakdown of food protein.  As kidney function decreases, the BUN level increases.

Some urine tests require only a few ounces of urine, and others require the collection of all urine produced over a 24-hour period.  A 24-hour urine test shows how much urine the kidneys produce in one day, and can be used to measure how much protein leaks from the kidneys into the urine.  Protein leakage can also be accurately determined in a small sample of urine by measuring its protein and creatinine concentrations.

A creatinine clearance test compares the creatinine in a 24-hour sample of urine to the creatinine level in the blood, to show how much blood the kidneys are filtering each minute.  The creatinine clearance can also be estimated accurately from the serum creatinine alone using well-established prediction equations.