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The glomerular filtration rate may be measured using inulin or iothalamate markers but is clinically impractical. The GFR allows for an easier method of determining kidney function by calculating the GFR.  Many labs now offer a calculated GFR using serum creatinine levels and equations such as the Modification of Diet in Renal Disease (MDRD) or the Chronic Kidney Disease Epidemiology Study (CKD-EPI). The normal values are as follows:

Males: 97-137 ml/min/1.73m2

Females: 88-128 ml/min/1.73m2

The value of the GFR may be calculated from a serum creatinine value, or may be obtained by measuring the creatinine clearance via a 24-hour urine collection or the Cockroft-Gault equation using the serum creatinine. The method using a 24-hour urine collection is the most accurate, but should only be performed once the serum creatinine has stabilized. The equations for calculating and measuring the creatinine clearance are as follows:

Twenty-four-hour urine collection:

Estimate using serum creatinine Cockroft-Gault method: