What is GFR (Glomerular Filtration Rate)?

When a person has chronic kidney disease (CKD), it means their kidneys are not working at full capacity. Because kidney function decreases over time, kidney disease has been divided into five stages. When someone is diagnosed with CKD, the next step is to determine the stage of the disease. That's where measuring the glomerular filtration rate (GFR) comes in.

How To Determine the Stage of Chronic Kidney Disease Using GFR

Kidney function is measured by how well the kidneys clean the blood. The GFR is a good way to find out a patient's stage of kidney disease. The main factor in estimating the GFR is finding out the level of creatinine in the blood. Your doctor will order blood tests that will list your serum creatinine, a waste product that comes from muscle activity. When kidneys are functioning, they remove creatinine from the blood. As kidney function slows, blood levels of creatinine rise.

A mathematical equation is used to estimate the GFR. In addition to serum creatinine, other factors in the equation include age and gender. Sometimes, optional factors such as weight, blood urea nitrogen (BUN) and serum albumin are used to get a patient's GFR level. Once the GFR level is known, the stage of kidney disease can be determined. See the chart below for the stages:

Early Indications and Symptoms of a Low GFR

As CKD progresses a patient may develop other problems including high blood pressure, anemia, malnutrition, bone disease and problems with the nervous system. Knowing the accurate GFR level helps doctors provide the proper treatment and medication dosages at each stage.

If you score above 60 mL/min on the GFR calculator, it doesn't necessarily mean you have Stage 1 or Stage 2 CKD; it does, however, apply to people with existing kidney damage. In Stage 1 and Stage 2 CKD, there are often few symptoms. Early CKD is usually diagnosed if there are other problems present such as:

• High blood pressure
• Higher than normal levels of creatinine or urea in the blood
• Blood or protein in the urine
• Evidence of kidney damage in an MRI, CT scan, ultrasound, or contrast X-ray
• A family history of polycystic kidney disease (PKD)

Since diabetes and high blood pressure are the top two causes of chronic kidney disease, these diseases must also be controlled. Managing blood sugar and blood pressure, plus taking prescribed blood pressure medication and limiting protein are recommended to help slow the progression of CKD.

In Stage 3 CKD, anemia (a shortage of red blood cells) and/or early bone disease may appear and should be treated to reduce problems down the road. As Stage 3 progresses, the National Kidney Foundation recommends the patient see a nephrologist—a doctor who specializes in treating kidney disease.

When CKD has progressed to Stage 4, it is time to begin preparing for dialysis and/or a kidney transplant. The patient should discuss the two types of dialysis—hemodialysis and peritoneal dialysis—with the doctor to determine which is best. If the patient will undergo hemodialysis, a fistula or graft vascular access can be put in to give it time to mature before dialysis begins. A catheter also needs to be put in place for peritoneal dialysis.

By Stage 5 CKD the kidneys can no longer clean the blood, so dialysis or a kidney transplant is needed for survival.

How to Calculate the GFR

Use DaVita's GFR Calculator to figure out a GFR. This calculator uses the formula for adults only. It will ask you to provide:

• Age (GFR decreases with age.)
• Serum creatinine (Measures waste product in the blood that comes from muscle activity.)
• Gender (Medical literature states that men usually have more muscle mass than women, so the calculation is adjusted based on gender.)

After submitting information, the GFR Calculator will tell you an estimated GFR level. Always consult a physician for more information about medical conditions.

The earlier kidney disease is detected, the better the chance of slowing or stopping its progression. The DaVita GFR Calculator was designed to help you learn about the stages of kidney disease and provide information about typical steps taken to ensure the best care. See your physician to get a diagnosis of chronic kidney disease and determine your stage.

Disclaimer: This is not designed to be a self-diagnostic tool. When using this GFR Calculator, you should not assume that you have or do not have CKD until your doctor has diagnosed you. GFR estimates may not be reliable in certain individuals. There are other factors besides chronic kidney disease that will increase GFR such as, muscle trauma, vigorous exercise, unusually high or low muscle mass (such as in athletes or malnourished individuals), unusually high or low dietary creatine (such as in those taking creatine supplements or vegetarians) and possibly other conditions. It is important that you talk to your doctor if you have any concerns about your kidney function or the results from using this calculator.