## eGFR

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Nephromatic uses two approaches to calculate the estimated glomerular filtration rate. The choice of CKD-EPI equation is based on whether creatinine, cystatin C, or both are entered.

## MDRD GFR

The MDRD GFR is an estimate of the glomerular filtration rate (GFR) using serum creatinine and demographic factors. It has not been studied extensively in populations that are not white or black. It relies on a stable creatinine and may be less accurate for GFR values above 60.

Nephromatic uses the simplified MDRD equation by Levey, et. al.

eGFR = 186*(0.742 if female)*(1.212 if Black)*creatinine^{-1.153}*age^{-0.203}

## CKD-EPI GFR

The CKD-EPI GFR is an estimate of the glomerular filtration rate (GFR) using serum creatinine and demographic factors. It is a relatively new equation proposed to be superior to the MDRD GFR equation. There are three different versions of this equation used.

The CKD-EPI creatinine equation by Levey, et. al.:

eGFR = 141 x min(Scr/k, 1)^{a} x max(Scr/k, 1)^{-1.209} x 0.993^{age} [ x 1.018 if female ] [ x 1.159 if
black ]

Scr is serum creatinine, k is 0.7 for females and 0.9 for males, a is
-0.329 for females and -0.411 for males.

The CKD-EPI cystatin C equation by Inker, et. al.:

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 ]

Scys is serum cystatin C.

The CKD-EPI creatinine-cystatin C equation by Inker, et. al.:

eGFR = 135 x min(Scr/k, 1)^{-a} x max(Scr/k, 1)^{-0.601} x min(Scys/0.8, 1)^{-0.375} x max(Scys/0.8, 1)^{-0.711} x 0.995^{age} [ x 0.969 if female ] [ x 1.08 if black ]

Scr is serum creatinine and Scys is serum cystatin C.

k is 0.7 for females and 0.9 for males

a is -0.248 for females and -0.207 for males

## CKD Staging

Chronic kidney disease (CKD) staging uses the National Kidney Foundation (NKF) staging system for individuals who have known kidney damage. CKD stage is determined from the CKD-EPI eGFR.

Recommendations are based on NKF guidelines for patients with CKD and may not be relevant in the acute setting.

### References

- (Levey AS, Greene T, Kusek J, Beck GJ, Group MS: A simplified equation to predict glomerular filtration rate from serum creatinine [Abstract]. J Am Soc Nephrol 11: A0828, 2000).
- Levey et al. A new equation to estimate glomerular filtration rate. Ann Intern Med (2009) vol. 150 (9) pp. 604-12.
- Inker et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med (2012) vol. 367 (1) pp. 20-9.