GFR Calculator - Estimated Glomerular Filtration Rate

This GFR calculator (estimated glomerular filtration rate calculator) is a tool that can help you with detecting a kidney disease at its early stage. Read on to get a better understanding of how it works, how to calculate the GFR from cystatin C and creatinine levels, and what values of estimated GFR (eGFR) are an alarming indicator.

The estimated glomerular filtration rate, or eGFR for short, is a parameter that determines the risk of kidney disease. It can be calculated from your blood test results. If may indicate that the kidneys don't function correctly.

The unit of eGFR is mL/min/1.73m². The value 1.73m² is the standardized body area - that's why none of the equations include a variable of height or weight.

It's important to remember that creatinine levels might differ depending on the sex and race of the patient. Also, muscle mass, physical activity, or cachexy have their influence on the blood test result. On the other hand, cystatin C levels are independent of muscle mass - the factors that may interfere are thyroid dysfunction and corticosteroid therapy.

There are four main equations that you can use to estimate GFR according to the National Institute of Diabetes and Digestive and Kidney Diseases. Our estimated glomerular filtration rate calculator uses all four of them. You can compare all results and see whether all of them are in the normal range. You can also choose whether you want to calculate eGFR based on serum creatinine or serum cystatin C levels. Or both!

Note that the estimated GFR calculator is suitable only for adults aged 19 or older. Use the pediatric eGFR calculator to calculate the estimated glomerular filtration rate of children.

1. CKD-EPI Creatinine Equation (2009)

This is the primary and most recommended method. It uses just one blood test result for serum creatinine.

eGFR = 141 × min(SCr/k, 1)^α × max(SCr/k, 1)^-1.209 × 0.993^Age × a × b

where:

• α is a coefficient dependent on sex: -0.329 for females, -0.411 for males;
• k is a coefficient dependent on sex: 0.7 for females, 0.9 for males;
• a is a coefficient dependent on sex: 1.018 for females, 1 for males;
• b is a coefficient dependent on race: 1.159 for black, 1 for other; and
• SCr is the level of standardized serum creatinine in mg/dL.

2. CKD-EPI Creatinine-Cystatin Equation (2012)

It's a version of the previous formula that also considers the level of serum cystatin C. It provides more accurate results for patients with unusual diet or extreme muscle mass.

eGFR = 135 × min(SCr/k, 1)^α × max(SCr/k, 1)^-0.601 × min(Scys/0.8, 1)^-0.375 × max(Scys/0.8, 1)^-0.711 × 0.995^Age × a × b

where:

• α is a coefficient dependent on sex: -0.248 for females, -0.207 for males;
• k is a coefficient dependent on sex: 0.7 for females, 0.9 for males;
• a is a coefficient dependent on sex: 1.969 for females, 1 for males;
• b is a coefficient dependent on race: 1.08 for black, 1 for other;
• SCr is the level of standardized serum creatinine in mg/dL; and
• Scys is the level of standardized serum cystatin C in mg/L.

3. CKD-EPI Cystatin C Equation (2012)

This equation considers only the level of serum cystatin C. It is a useful formula for patients with unstable creatinine concentration (for example, pregnant women), as well as a confirmatory test after applying the previous two equations.

eGFR = 133 × min(Scys/0.8, 1)^-0.499 × max(Scys/0.8, 1)^-1.328 × 0.996^Age × a

where:

• α is a coefficient dependent on sex: 0.932 for females, 1 for males; and
• Scys is the level of standardized serum cystatin C in mg/L.

4. MDRD Study Equation

This equation is an alternative to the CKD-EPI equations composed by the Chronic Kidney Disease Epidemiology Collaboration. The MDRD equation stands for Modification of Diet in Renal Disease; it has been proven correct for patients between 18 and 70 years old and returns correct values for all patients with common causes of kidney disease.

eGFR = 175 × SCr^-1.154 × Age^-0.203 × a × b

where:

• a is a coefficient dependent on sex: 0.742 for females, 1 for males;
• b is a coefficient dependent on race: 1.212 for black, 1 for other; and
• SCr is the level of standardized serum creatinine in mg/dL.

Now that you know how to calculate the GFR (and have used our eGFR calculator to find out yours), you probably wonder what the results mean. The table below shows the typical values of eGFR on different stages of kidney malfunction, basing on the data presented by the National Kidney Foundation.

Remember that the results may differ between different people based on numerous factors. Consult a doctor in case of any doubts.

In most cases, chronic kidney disease is caused by diabetes or high blood pressure. The other common causes of CKD are immunological or inherited diseases.

If CKD is diagnosed at an early stage, it may be slowed down or brought to a stop. In the most advanced stages of CKD, the patient may require dialysis or a kidney transplant.

If this topic is of interest to you, check the kidney failure risk calculator.