Glomerular Filtration Rate (GFR) and Kidney Function

Most people know that their blood pressure and cholesterol numbers are important in evaluating their risk for heart and blood vessel disease. Yet few know about the number that indicates the health of their kidneys. This important number is the glomerular filtration rate (GFR). GFR tells a lot about how well your kidneys are working.

The kidneys perform several important jobs. One job is to remove wastes and excess fluid from the blood. When your kidneys are working well, wastes and excess fluid are removed to become part of the urine your body makes each day. When kidneys aren't working well, they don't filter the way they should. Important substances that should remain in the body, for example protein, are filtered out, and wastes that should be removed build up in the blood.

People don't always know if something is wrong with their kidneys. Early kidney disease can be silent, without pain or other symptoms. A person may not suspect that they have kidney disease. In more advanced kidney disease, some people notice problems such as swelling, high blood pressure, poor appetite and nausea and vomiting.

Your GFR number is an estimate of how much kidney function you have. GFR is the best way to check kidney function. If your GFR number is low, your kidneys are not functioning well. Having your GFR checked will help find kidney disease. Early detection means early treatment, and early treatment can slow down the complications of kidney disease.

GFR can't be measured directly. It needs to be estimated using a mathematical formula from the amount of creatinine in your blood along with other factors like your age, race and gender. Creatinine is a waste product created by your body's muscles. Your kidneys usually keep the level of creatinine just right. The creatinine level alone is not the best way to check kidney function, but it is an important blood test because it is used to estimate GFR.

Ask your health care professional what your GFR is and what your number means for you. Generally:

  • In adults, the normal GFR number is 90 or higher
  • Having a GFR between 60 and 89 may be normal for some people, including those over age 60. GFR tends to decline as we age even in people without kidney disease. These people may need to have GFR checked more often in the future. They may be asked to avoid medications that can damage the kidneys (such as ibuprofen and other non-steroidal anti-inflammatory agents) or reduce the dose of medicines that are removed by the kidneys
  • A GFR below 60 is abnormal. The GFR test should be repeated. GFR below 60 that persists for 3 months or more means chronic kidney disease. Your health care professional may refer you to a nephrologist (kidney specialist) for evaluation and treatment. A GFR below 15 indicates kidney failure. Someone with kidney failure needs dialysis or a kidney transplant to survive

If your GFR is abnormal, additional evaluation is done to give more information. Tests may include:

  • Urine tests that look for:
    • the type and amount of protein in the urine. Persistent protein in urine (proteinuria) is not normal; it is an early sign of kidney damage
    • red blood cells. Red blood cells in the urine (hematuria) is abnormal; it is a sign of bleeding in the urinary system
    • white blood cells. White blood cells in the urine (pyuria) is a sign of infection.
  • Ultrasound or CT scan to get a picture of your kidneys and urinary system. These pictures show the size of your kidneys and whether or not tumors, kidney stones or cysts are present.
  • A kidney biopsy to remove a tiny piece of the kidney for evaluation. The sample is studied under a microscope to see what kind of kidney damage is happening.

If a sign of kidney damage is found, even if GFR is normal, a person may still have chronic kidney disease (CKD). CKD is defined as:

  • GFR below 60 for 3 or more months, or
  • Sign(s) of kidney damage for 3 or more months regardless of the GFR level.

Through its Kidney Early Evaluation Program (KEEP™) initiative, the National Kidney Foundation offers free health screenings throughout the United States for anyone 18 years and older with high blood pressure, diabetes or a family history of kidney disease. To find our where and when a KEEP screening is being offered, visit www.kidney.org. You can search by zip code. KEEP offers a health risk examination, blood pressure measurement, and blood and urine tests. Some of the results from these tests will be available on-site. There is also an opportunity to discuss these results with health care professionals on-site.

Kidney disease is a progressive disease. The earlier it is found, the better. When it is found and treated early, it may be possible to slow the progression. The success of treatment depends on:

  • The stage of kidney disease when treatment is started. Treatment will depend on the stage of kidney disease and other existing health problems. The earlier it's started, the better a person is likely to do.
  • How carefully the treatment plan is followed
Questions you may want to ask your doctor include:
  • Am I at increased risk for kidney disease? What makes me at risk?
  • What is my GFR?
  • Do I have chronic kidney disease? If yes, what stage do I have? How can I slow the progression?
  • What is my blood pressure? Is it within the recommended target range? If not, what can I do to get it to target?

For further information, contact the National Kidney Foundation:

National Office
800.622.9010 (toll free)
www.kidney.org

Local Affiliate or Division
www.kidney.org/about/offices.cfm

KEEP Kidney Screenings
www.kidney.org/news/keep/index.cfm