# eGFR Equations for Adults

Estimate glomerular filtration rate (GFR) in individuals ages 18 and older using the following race-free Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations

- 2021 CKD-EPI creatinine equation (2021 CKD-EPI eGFRcr)
- 2021 CKD-EPI creatinine-cystatin C equation (2021 CKD-EPI eGFRcr-cys)
- 2012 CKD-EPI cystatin C equation (2012 CKD-EPI eGFRcys)

Using both creatinine and cystatin C to estimate GFR is preferred and is more accurate than using serum creatinine alone. However, a single parameter equation may be preferred when important non-GFR determinants are present in a given individual, for either creatinine or cystatin C. Using the combined creatinine-cystatin C equation is particularly important when the estimated GFR (eGFR) is close to a critical decision value, such as in certain cases of drug dosing or kidney transplant evaluation. Using the combined creatinine-cystatin C equation may also be particularly important when assessing racial disparities in risk of kidney failure or death in Black versus White United States-based populations. Use of the 2021 CKD-EPI eGFRcr equation appears to diminish the true difference in these disparities compared to the 2021 CKD-EPI eGFRcr-cys, the 2012 CKD-EPI eGFRcys, and the 2009 race-based CKD-EPI eGFR equations.^{1}

## Limitations of the 2021 CKD-EPI eGFRcr Equation

Although combined use of creatinine and cystatin C is preferred, cystatin C is not currently routinely assessed in clinical contexts. Therefore, the 2021 CKD-EPI eGFRcr equation is likely to become the most widely used equation in the near future. Thus, it is particularly important to acknowledge its limitations. Estimated GFR calculated using the 2021 CKD-EPI eGFRcr equation may be less precise compared to the 2021 CKD-EPI eGFRcr-cys, the 2012 CKD-EPI eGFRcys, and the 2009 race-based CKD-EPI equations.^{1,2,3,4} On average, the 2021 CKD-EPI eGFRcr appears to overestimate GFR by about 4% in non-Black individuals while underestimating GFR by about -4% in Black individuals.

Decisions on how to best account for small biases in various eGFR calculations when clinical decisions are being made, such as with drug dosing and listing for kidney transplant, can be individualized by health care teams based on conditions specific to each patient.

## Equations

NIDDK calculates eGFR using creatinine determinations that are traceable to an isotope dilution mass spectrometry (IDMS) reference measurement procedure and cystatin C determinations that are traceable to ERM-DA471_IFCC HUMAN SERUM (cystatin C) certified reference material.

### 2021 CKD-EPI Creatinine Equation

The 2021 CKD-EPI eGFRcr equation estimates GFR using age, sex, and serum creatinine.^{2}

The equation can be expressed as a single equation:

**eGFR = 142 × min(SCr/κ,1) ^{α} × max(SCr/κ,1)^{-1.200} × 0.9938^{Age} × 1.012 [if female]**

Abbreviations/units

- eGFR = estimated GFR in mL/min/1.73 m
^{2} - SCr = standardized serum creatinine in mg/dL
- κ = 0.7 (females) or 0.9 (males)
- α = -0.241 (females) or -0.302 (males)
- min = indicates the minimum of SCr/κ or 1
- max = indicates the maximum of SCr/κ or 1
- age = years

Alternately, the equation can be expressed as a series of equations for different sex and creatinine conditions, as shown in Table 1.

**Table 1. 2021 CKD-EPI eGFRcr equation for estimating GFR expressed for specified sex and serum creatinine (conventional units)**

Sex | Serum creatinine, SCr (mg/dL) | Equation (age in years for ≥ 18) |
---|---|---|

female | ≤ 0.7 | GFR = 142 × (SCr/0.7)^{-0.241} × (0.9938)^{Age} × 1.012 |

female | > 0.7 | GFR = 142 × (SCr/0.7)^{-1.200} × (0.9938)^{Age} × 1.012 |

male | ≤ 0.9 | GFR = 142 × (SCr/0.9)^{-0.302} × (0.9938)^{Age} |

male | > 0.9 | GFR = 142 × (SCr/0.9)^{-1.200} × (0.9938)^{Age} |

GFR conversion factors

- GFR mL/min/1.73 m
^{2}to mL/s/1.73 m^{2}, multiply by 0.0167 - serum creatinine µmol/L to mg/dL, divide by 88.4

### 2021 CKD-EPI Creatinine-cystatin C Equation

The 2021 CKD-EPI eGFRcr-cys equation calculates eGFR using age, sex, serum creatinine, and serum cystatin C.^{3}

The equation can be expressed as a single equation:

**eGFR = 135 × min(SCr/κ,1) ^{α} × max(SCr/κ,1)^{-0.544} × min(Scys/0.8,1)^{-0.323} × max(Scys/0.8,1)^{-0.778} × 0.9961^{Age} × 0.963 [if female]**

Abbreviations/units

- eGFR = estimated GFR in mL/min/1.73 m
^{2} - SCr = standardized serum creatinine in mg/dL
- Scys = standardized serum cystatin C in mg/L
- κ = 0.7 (females) or 0.9 (males)
- α = -0.219 (females) or -0.144 (males)
- min = indicates the minimum of SCr/κ or 1
- max = indicates the maximum of SCr/κ or 1
- age = years

GFR conversion factors

- GFR mL/min/1.73 m
^{2}to mL/s/1.73 m^{2}, multiply by 0.0167 - serum creatinine µmol/L to mg/dL, divide by 88.4
- cystatin C does not require unit conversion

Alternately, the equation can be expressed as a series of equations for different sex, creatinine, and cystatin C conditions, as shown in Table 2.

**Table 2. 2021 CKD-EPI eGFRcr-cys equation for estimating GFR expressed for specified sex, serum creatinine, and cystatin C (conventional units)**

Sex | Serum creatinine, SCr (mg/dL) | Serum cystatin C (mg/L) | Equation (age in years for ≥ 18) |
---|---|---|---|

female | ≤ 0.7 | ≤ 0.8 | GFR = 135 × (SCr/0.7)^{-0.219} × (Scys/0.8)^{-0.323} × (0.9961)^{Age} x 0.963 |

female | ≤ 0.7 | > 0.8 | GFR = 135 × (SCr/0.7)^{-0.219} × (Scys/0.8)^{-0.778} × (0.9961)^{Age} x 0.963 |

female | > 0.7 | ≤ 0.8 | GFR = 135 × (SCr/0.7)^{-0.544} × (Scys/0.8)^{-0.323} × (0.9961)^{Age} x 0.963 |

female | > 0.7 | > 0.8 | GFR = 135 × (SCr/0.7)^{-0.544} × (Scys/0.8)^{-0.778} × (0.9961)^{Age} x 0.963 |

male | ≤ 0.9 | ≤ 0.8 | GFR = 135 × (SCr/0.9)^{-0.144} × (Scys/0.8)^{-0.323} × (0.9961)^{Age} |

male | ≤ 0.9 | > 0.8 | GFR = 135 × (SCr/0.9)^{-0.144} × (Scys/0.8)^{-0.778} × (0.9961)^{Age} |

male | > 0.9 | ≤ 0.8 | GFR = 135 × (SCr/0.9)^{-0.544} × (Scys/0.8)^{-0.323} × (0.9961)^{Age} |

male | > 0.9 | > 0.8 | GFR = 135 × (SCr/0.9)^{-0.544} × (Scys/0.8)^{-0.778} × (0.9961)^{Age} |

### 2012 CKD-EPI Cystatin C Equation

The 2012 CKD-EPI eGFRcys equation estimates GFR using age, sex, and serum cystatin C.^{5}

**eGFR = 133 x min(Scys/0.8, 1) ^{-0.499} x max (Scys/0.8, 1)^{-1.328} x 0.996^{Age} x 0.932 [if female]**

Abbreviations/units

- eGFR = estimated GFR in mL/min/1.73 m
^{2} - Scys = standardized serum cystatin C in mg/L
- min = indicates the minimum of Scys/0.8 or 1
- max = indicates the maximum of Scys/0.8 or 1
- age = years

GFR conversion factors

- GFR mL/min/1.73 m
^{2}to mL/s/1.73 m^{2}, multiply by 0.0167 - cystatin C does not require unit conversion

### European Kidney Function Consortium (EKFC) equations

The EKFC equations provide estimates of GFR across a wide age spectrum—from children older than 2 years to adults.^{6,7}As full age spectrum equations, the EKFC equations can be used continuously for patients transitioning from pediatric to adult care. Learn more about the EKFC equations.