How to Read the Results of Kidney Function Tests

Kidney function tests can help your physician detect problems early.
Kidney function tests can help your physician detect problems early. (Image: lab tools image by PHOTOFLY from

The kidneys are workhorses. These two small organs filter roughly 200 quarts of blood every day to eliminate excess water and waste, producing about 2 quarts of urine. When the kidneys are not functioning optimally, waste products begin to accumulate in the body, causing disease. In severe cases, these vital organs can fail, a potentially fatal event. According to the National Kidney Foundation, 26 million Americans have impaired renal function, otherwise known as chronic kidney disease. People who have high blood pressure, diabetes or a family history of kidney disease are more likely to develop kidney problems. Severe traumatic injury and childhood or genetic disorders can also damage the kidneys.

Check the lab report for the serum creatinine level. This shows the amount of creatinine found in your blood. Creatinine is a waste product derived from creatine, a component of muscle tissue. A creatinine test measures how effectively your body is eliminating creatinine. If your blood contains a high level of creatinine, it means your kidneys are not filtering out enough. The measurement of serum creatinine is reported in milligrams per deciliter. The normal range is 0.8 to 1.4 mg/dL.

Look for the glomerular filtration rate, or GFR. The GFR is the most informative test of overall kidney function. It evaluates how effectively the kidneys filter out waste products in the blood. Your physician will use your age, sex, serum creatinine level and other characteristics to calculate this value. A normal GFR is 30 or higher.

Find the letters BUN on your lab report. The BUN (blood urea nitrogen) measurement reveals how much urea nitrogen, a byproduct of protein, your blood contains. Urea nitrogen is one of the waste products your kidneys filter out under normal conditions. BUN is reported in milligrams per deciliter. The normal range of BUN is 7 to 20 mg/dL.

Check for urine protein test results. This simple urine test can determine whether you have excessive amounts of protein in your urine. If you do, it may be a sign of kidney disease. This test is usually repeated to ensure that the high protein level is persistent and not just a temporary occurrence. The measurement is reported in milligrams per deciliter. The normal range of protein in the urine for a random sample is 0 to 8 mg/dL. For a 24-hour urine test, the normal range is 150 mg or less.

Look for the entry "creatinine clearance." If you had both urine and blood levels of creatinine measured, your doctor may compare them as another way to calculate the glomerular filtration rate. The creatinine clearance test is reported in milliliters per minute. The normal range for women is 88 to 128 mL/min. For men, it is 97 to 137 mL/min.

Tips & Warnings

  • For more information on interpreting the results of your lab tests, talk to your physician. Another resource is the National Kidney and Urologic Diseases Information Clearinghouse (see Resources).
  • If you find an abnormal value on your lab report, try not to panic. Your doctor can explain whether there is cause for concern. Some conditions and drugs can cause some test levels to be higher or lower than normal.

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