eGFR mL/min/1.73m² | Kidney function |
---|---|

≥90 | Normal |

60-89 | Mildly decreased |

45-59 | Mildly to moderately decreased |

30-44 | Moderately to severely decreased |

15-29 | Severely decreased |

<15 | Kidney failure |

# 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 creatinine and cystatin C levels, and what values of estimated GFR (eGFR) are an alarming indicator.

## What is eGFR?

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 the result is low, it may indicate that your kidneys don't function correctly; in the worst case, you might have chronic kidney disease. The faster it is diagnosed, the better are the chances for an effective treatment.

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 sex and race of a 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.

## How to calculate GFR?

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 basic 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
- 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 takes into account 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
- Scys is the level of standardized serum cystatin C in mg/L.

**3. CKD-EPI Cystatin C Equation (2012)**

This equation takes into consideration 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
- Scys is the level of standardized serum cystatin C in mg/L.

**4. MDRD Study Equation**

This 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
- SCr is the level of standardized serum creatinine in mg/dL.

## What levels of estimated GFR are alarming?

Now that you know how to calculate the GFR (and have used our eGFR calculator to find out yours), you probably wonder what do 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.

eGFR [mL/min/1.73m²] | Kidney function |
---|---|

90 or above | No kidney damage or mild kidney damage |

60-89 | Kidney damage with mild loss of kidney function |

45-59 | Mild to moderate loss of kidney function |

30-45 | Moderate to severe loss of kidney function |

15-29 | Severe loss of kidney function |

Less than 15 | Kidney failure |

Even if your eGFR is mildly decreased (to 60-89), it still **does not necessarily mean you are in danger** of kidney malfunction. First of all, the level of eGFR decreases with age; the normal eGFR of people aged 70 or older is only 75. Moreover, you should monitor the levels of creatinine and cystatin C to check whether this lowering of eGFR is a long-term condition.

Only if the estimated glomerular filtration rate is **below 60 for 3 months** straight (or if you have other **worrying symptoms**, including high levels of albumin in your urine), it means that you may have **chronic kidney disease** (CKD). Make sure to visit your doctor! He may suggest further tests, such as a simple urine test or kidney biopsy.

## How to deal with chronic kidney disease?

If you have some of the symptoms of CKD - **lowered eGFR** or worrying **markers in your urine** occurring for **longer than three months** - you may have the chronic kidney disease. In 2 out of 3 cases, it is caused by **diabetes** or **high blood pressure**. The other common causes of CKD are immunological or inherited diseases.

If your CKD was diagnosed at an early stage, you're lucky - it can be slowed down or brought to a complete stop. With proper monitoring, you may never experience major kidney problems. If, on the other hand, your kidneys are in an alarming state (at the end stage of kidney disease), you may require dialysis or a kidney transplant.