06/03/2011What is a Glomerular Filtration Rate, or GFR?

Abida Zafar, MD

GFR stands for Glomerular Filtration Rate. It gives an estimate of the degree of kidney function. The GFR is equal to the sum of the filtration rates in all of the functioning nephrons, thus the GFR gives a rough measure of the number of functioning nephrons.

The normal value for GFR depends on age, sex, and body size, and is approximately 130 and 120 mL/min/1.73m2 for men and women, respectively, with considerable variation even among normal individuals.

The most common method utilized to estimate the GFR is the MDRD (Modification of Diet in Renal Disease Study). The most accurate method to calculate GFR is inulin clearance, but it is not clinically used as inulin is expensive and difficult to assay. The GFR is used to stage the degree of impairment of renal function with Stage 1 being kidney damage with normal or increased GFR (greater than 90mL/min/1.73m2), Stage 2 with kidney damage and mild decrease in GFR (60-89 mL/min/1.73m2), Stage 3 with moderate decrease in GFR (30-59 mL/min/1.73m2, Stage 4 with severe decrease in GFR(15-29 mL/min/1.732), and Stage 5 with GFR of less than 15 mL/min/1.73m2. This stage also includes patients with ESRD on dialysis.

Thus, GFR is a very important value for all patients with CKD (Chronic Kidney Disease). Change in GFR is very crucial in the management of patients with CKD and therefore all patients should know their baseline GFR and stage of kidney disease.

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