Article: Medical Tests of Kidney Function

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Healthy kidneys remove wastes and excess fluid from the blood. Blood tests show whether the kidneys are failing to remove wastes. Urine tests can show how quickly body wastes are being removed and whether the kidneys are leaking abnormal amounts of protein.

Blood Tests

Serum creatinine. Creatinine (kree-AT-uh-nin) is a waste product that comes from meat protein in the diet and from the normal wear and tear on muscles of the body. Creatinine levels in the blood can vary, and each laboratory has its own normal range. In many labs the normal range is 0.6 to 1.2 mg/dL. 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 (yoo-REE-uh NY-truh-jen) also is produced from the breakdown of food protein. A normal BUN level is between 7 and 20 mg/dL. As kidney function decreases, the BUN level increases.

Urine Tests

Some urine tests require only a few ounces of urine. But some tests require collection of all urine produced for a full 24 hours. A 24-hour urine test shows how much urine your kidneys produce in 1 day. The test is sometimes used to measure how much protein leaks from the kidney into the urine in 1 day. However, protein leakage can also be accurately determined in a small sample of urine by measuring its protein and creatinine concentration.

Creatinine Clearance

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

More information is available from

American Kidney Fund
6110 Executive Boulevard
Suite 1010
Rockville, MD 20852
Phone: 1-800-638–8299 or (301) 881-3052
Email: helpline@akfinc.org
Internet: www.akfinc.org

National Kidney Foundation
30 East 33rd Street
New York, NY 10016
Phone: 1-800-622–9010 or (212) 889-2210
Email: info@kidney.org
Internet: www.kidney.org


Source: National Institute of Diabetes and Digestive and Kidney Diseases
Cache Date: December 10, 2004

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