## Tool to estimate glomerular filtration

### Estimated GFR using the BSA adjusted CKD-EPI model:²

##### References:

1. Janowitz T, Williams EH, et al. A new model for estimating glomerular filtration rate in patients with cancer.

2. Levey AS, Stevens LA, Schmid CH, Zhang Y, Castro AF, Feldman HI, et al. A New Equation to Estimate Glomerular Filtration Rate. Ann Intern Med. 2009;150:604-612.

3. DuBois D, DuBois E. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916;17:863–71.

This tab shows the histogram of the data used to develop the model with the input values shown as a red vertical line. The maximum and minimum of the variables are shown as grey vertical lines. The data input data values should not be outside the range of the data used to develop the model

### The new equation used to predict this value is as follows:

\begin{align} \sqrt{\mathrm{GFR}} &= 1.8140 + 0.01914\mathrm{Age} + 4.7328\mathrm{BSA} - 3.7162\log(\mathrm{Cre}) - 0.9142\log(\mathrm{Cre})^2 \nonumber \\ & \quad + 1.0628\log(\mathrm{Cre})^3 - 0.0297\mathrm{Age}\times\mathrm{BSA} + \left(0.0202 +0.0125\mathrm{Age}\right)[\mathrm{if} \, \mathrm{Sex=Male}] \nonumber \end{align}
where:
• GFR is Glomerular filtration rate with units ml/min
• Age has the units years
• BSA is body surface area with units m² calculated using the DuBois equation
• Cre is blood serum creatinine concentration with units mg/dL
and the coefficients in the equation have been rounded to 4 decimal places.

### The CKD-EPI equation takes the following form:

$$\mathrm{GFR_{nonadjusted}} = \begin{cases} 141 \times \mathrm{min} \left(\frac{\mathrm{Cre}}{0.7}, 1\right)^{-0.329} \times \mathrm{max} \left(\frac{\mathrm{Cre}}{0.7}, 1 \right)^{-1.209} \times \mathrm{Age}^{0.993} \times 1.018 & \mathrm{if} \, \mathrm{Sex=Female} \\ 141 \times \mathrm{min} \left(\frac{\mathrm{Cre}}{0.9}, 1\right)^{-0.411} \times \mathrm{max} \left(\frac{\mathrm{Cre}}{0.9}, 1 \right)^{-1.209} \times \mathrm{Age}^{0.993} & \mathrm{if} \, \mathrm{Sex=Male} \end{cases}$$
where GFR now has the units ml/min/1.73m² and all other variables have the same units as above. This non adjusted estimated GFR value is then BSA-adjusted by the following equation
$$\mathrm{GFR_{adjusted}} = \mathrm{GFR_{non adjusted}} \times \frac{1.73}{\mathrm{BSA}}$$