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Calculate Your Glomerular Filtration Rate

Kidney function is measured by how well the kidneys clean the blood. The glomerular filtration rate (GFR) is a good way to find out the 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. This is 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, factors in the equation include age, race and gender. Sometimes optional factors such as weight, blood urea nitrogen and serum albumin are used to get the patient's GFR level. Once the GFR level is known, the stage of kidney disease can be determined.

5 Stages of Chronic Kidney Disease

Stage GFR Level Description

Stage 1

90 ml/min or more

Healthy kidneys or kidney damage with normal or high GFR

Stage 2

60 to 89 ml/min

Kidney damage and mild decrease in GFR

Stage 3

30 to 59 ml/min

Moderate decrease in GFR

Stage 4

15 to 29 ml/min

Severe decrease in GFR

Stage 5

Less than 15 ml/min or on dialysis

Kidney failure


How to Figure Out the GFR

The earlier kidney disease is detected, the better the chance of slowing or stopping its progression. DaVita's 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. It is intended to calculate GFR in adults only. (This calculator uses the formula for adults only.) See your physician to get a diagnosis of chronic kidney disease and determine your stage.

The following table details the information the calculator will request, and the reason for each piece of information.

Information Requested Reason for Asking

Age

GFR decreases with age and disease.

Serum creatinine

Measures waste product in blood that comes from muscle activity. The kidneys usually remove creatinine. When kidney function slows, creatinine rises. This result can be obtained from the blood work ordered by a doctor.

Gender

Medical literature states that men usually have more muscle mass than women, so the calculation is adjusted based on gender.

Race

Medical literature states that people of African descent usually have more muscle mass than other ethnicities, so the calculation is adjusted based on race.

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

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 vegetarians or those taking creatine supplements ) and other conditions. It is important that you talk to your doctor if you have any concerns about your kidney function or the results from this calculator.

Understand How Well Dialysis Is Cleaning Your Blood

The Kt/V calculator is a tool nephrologists use to determine the adequacy of dialysis treatment.

Kt/V is a mathematical formula: K (clearance) multiplied by t (time) divided by V (volume):

K = clearance — the amount of urea your dialyzer can remove (liters/minute)
t = time — the duration of treatment (minutes)
V = volume — the amount of body fluid (liters)

For example, if you have 50 liters of body fluid and a dialyzer with a clearance of 0.25 L/min, to get a Kt/V of 1.2, you would need 240 minutes (4 hours) of dialysis per treatment. To clean your blood well, the dialyzer clearance rate (K) multiplied by the time on dialysis (t) should equal a little more than the total volume of fluid in your body (V) that needs to be cleaned.

In continuous ambulatory peritoneal dialysis (CAPD), the guidelines recommend a weekly Kt/V of at least 2.0, taking into account any remaining kidney function along with the CAPD treatment. In hemodialysis patients, a blood sample is taken at the start and end of a dialysis session. Information about your treatment is collected, and a computer calculates the Kt/V result. In peritoneal dialysis, Kt/V is measured by collecting drained dialysate along with any urine you produce in a 24-hour period.

These lab tests are done once a month for hemodialysis patients and once every four months for peritoneal dialysis patients or after a prescription change. Ask your doctor what your values are each time. If your values do not reach adequate numbers, work with your care team to raise your dialysis dose.

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