The glomerular filtration rate (GFR) is a lab value that looks at kidney function. While you may recognize the GFR as a result that simply comes back on the lab slip, it’s important to note that this result is based on a calculation that includes serum creatinine, age and gender. There are several estimation equations and even online calculators; the American Society of Nephrology and National Kidney Foundation recommends the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.
CKD-EPI Equation (Inker & Perrone, 2021)
This equation no longer contains a factor for race and may underestimate GFR in Black patients and overestimate GFR in others. This equation was developed to provide a more accurate estimate of GFR in individuals with normal or only mildly reduced GFR (above 60 mL/min/1.73m2
) and should only be used in patients with stable kidney function. It is important to note that eGFR equations that include creatinine will be less accurate in individuals with factors that affect serum creatinine such as a high or low muscle mass or creatinine intake, patients with cirrhosis, chronic heart failure, amputations, neuromuscular disease, or those with high-protein or vegetarian diets. A confirmation test may be required including both a cystatin C and creatinine test, or a timed urine collection for creatinine clearance.