Why estimate GFR?
The gold standard for measurement of GFR is kidney clearance of inulin, but this method is a research tool and not practical for clinical practice. GFR may be accurately measured by determining the clearance rate of exogenous radioisotopes, such as radiolabelled Cr51-EDTA. Alternatively, the measurement of 24-hour creatinine clearance provides a reasonable, though less accurate, approximation. Both methods are inconvenient, time-consuming and costly. Serum creatinine concentration is widely used as a surrogate marker of GFR, but is crude and insensitive. For example, among the nationally representative AusDiab cohort of 11 247 Australian adults, 1.1% had elevated serum creatinine levels whereas 11.2% had a calculated GFR < 60mL/min.2 Because of these anomalies, much effort has been directed at deriving formulas that use serum creatinine level together with other clinical variables, such as age, sex and weight, to yield an accurate estimated GFR (eGFR). The abbreviated MDRD (Modificatio
