To improve the usefulness of the serum creatinine concentration as a marker of kidney function, prediction equations were developed.4,5 To more accurately predict GFR, these formulas take into account a patient's race, age, gender, and body surface area, in addition to serum creatinine concentration. The 2 most commonly used formulas are shown in Table 3. The Cockcroft-Gault equation is easy to use but may represent a slight overestimation of GFR. The Modification of Diet in Renal Disease (MDRD) equation is more accurate; moreover, an easy-to-use, modified version of this equation has been developed.6 Currently, these equations are readily available on most personal digital assistant medical calculation programs or online. Neither formula should be used unless a patient's renal function is in steady state. Rapidly changing creatinine levels, such as are seen in acute renal failure, render these equations useless. However, the MDRD equation is frequently used to estimate GFR in many clinical settings.

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