Estimating Glomerular Filtration Rate (GFR) in Adults

Primary Calculation Method

The American College of Cardiology recommends using the 2021 CKD-EPI creatinine equation without race as the standard method for estimating GFR in adults, which requires only serum creatinine, age, and sex 1, 2
The CKD-EPI 2021 equation uses standardized serum creatinine, incorporates patient age and sex, and does not use race as a variable, providing more accurate estimates than MDRD, especially at GFR >60 mL/min/1.73 m² 1, 2
Serum creatinine must be measured using assays calibrated to isotope-dilution mass spectrometry (IDMS) and traceable to international reference standards, with values <1 mg/dL reported to two decimal places 2

The National Kidney Foundation recommends adding cystatin C measurement and using the combined CKD-EPI creatinine-cystatin C equation when extremes of muscle mass, advanced cirrhosis, cancer, or eGFR 45-59 mL/min/1.73 m² without other markers of kidney damage are present 1, 2
The Cockcroft-Gault equation (1976) may overestimate kidney function in CKD stages 3-5 and is less accurate than CKD-EPI, requiring body weight and serum creatinine 1, 2, 3, 4
The MDRD equation (1999) is more accurate than Cockcroft-Gault for GFR <90 mL/min/1.73 m² but not valid for eGFR >60 mL/min/1.73 m² and has been superseded by CKD-EPI 2021 3, 5

The American Academy of Pediatrics recommends using pediatric-specific equations, such as the Schwartz equation and its modifications, or the Full Age Spectrum (FAS) equation, for children 4
For glomerular disease patients, no eGFR equation has been specifically validated, and hypoalbuminemia, glucocorticoids, and low muscle mass may affect eGFR estimates, considering measured GFR using exogenous markers for critical decisions 4, 2

Measured GFR (using iohexol or radioisotopic markers) should be considered when precise GFR measurement is critical for clinical decision-making, extremes of age or body size, calculating doses of potentially toxic drugs excreted by kidneys, or acute kidney injury 4, 2, 3
The National Institute of Diabetes and Digestive and Kidney Diseases recommends requesting laboratories to automatically report eGFR using CKD-EPI 2021 whenever serum creatinine is ordered, and not using serum creatinine alone to assess kidney function 2, 3