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 leaking abnormal amounts of protein.

NORMAL FINDINGS

Blood Tests

Serum creatinine. Creatinine is a waste product that comes from 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.

Normal findings: 0.6 to 1.2 mg/dL

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

Normal findings: 7-20 mg/dL

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

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. This is to show how many milliliters of blood the kidneys are filtering out each minute (mL/min). The creatinine clearance can also be estimated from the serum creatinine alone using well established prediction equations.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.