KIDNEY FUNCTION TESTS

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 also 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 also comes 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 also can give an accurate measurement of how much protein leaks from the kidney into the urine in 1 day.

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).