16th May 2025

Estimating renal function

The gold standard for measuring glomerular filtration rate (GFR) is by directly measuring the plasma or urinary clearance of an exogenous filtration marker, however this is difficult in practice. In practice GFR can be estimated with equations that use serum creatinine and other variables. Estimated glomerular filtration rate (eGFR) can be commonly calculated based on the Modification of Diet in Renal Disease (MDRD) equation or Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Creatinine clearance (ClCr) which is calculated from the Cockcroft-Gault formula is also commonly used to estimate renal function.

In patients with extremes of muscle mass eGFR should be used with caution. Reduced muscle mass can lead to overestimation of GFR, and increased muscle mass will result in an underestimation. In patients of average height and weight eGFR can be used to dose medications as opposed to ClCr. In toxic drugs, elderly patients, and extremes of muscle mass ClCr is recommended.