What is the best method to calculate estimated Glomerular Filtration Rate (eGFR)?

Best Method to Calculate eGFR

For routine clinical practice in adults, use the 2021 CKD-EPI creatinine equation without race as your standard first-line method for estimating GFR. 1, 2, 3

Initial Assessment Approach

• Start with creatinine-based eGFR (eGFRcr) using the 2021 CKD-EPI equation for the majority of adults without conditions affecting serum creatinine independent of GFR 1
• This equation requires only serum creatinine, age, and sex—no race variable 1, 3
• The 2021 CKD-EPI equation is more accurate than older equations (MDRD, Cockcroft-Gault), particularly at GFR >60 mL/min/1.73 m² 3, 4

Laboratory Requirements for Accuracy

• Serum creatinine must be measured using assays calibrated to isotope-dilution mass spectrometry (IDMS) and traceable to international reference standards 2, 3
• Values <1 mg/dL should be reported to two decimal places 2
• Request that your laboratory automatically reports eGFR using CKD-EPI 2021 whenever serum creatinine is ordered 2, 3

When to Add Cystatin C (Combined eGFRcr-cys)

Use the combined CKD-EPI creatinine-cystatin C equation in these specific situations: 1

• Extremes of muscle mass (very high or very low) 1, 3
• Extremes of body weight or composition 1
• Advanced cirrhosis 1, 3
• Cancer with high cell turnover 1
• eGFRcr 45-59 mL/min/1.73 m² without other markers of kidney damage (for confirmation) 2, 3
• Dietary factors affecting creatinine (vegetarian diet, creatine supplements) 1, 3

The combined equation (eGFRcr-cys) is more accurate than either marker alone, with coefficients of variation <10% and improved agreement across manufacturers 1

When to Measure GFR Directly (mGFR)

Consider measured GFR using exogenous markers (iohexol, iothalamate, or radioisotopic markers) when: 1, 3

• Precise GFR measurement is critical for clinical decision-making (e.g., kidney-cleared chemotherapeutic agents) 1
• Even combined eGFRcr-cys is thought to be inaccurate 1
• Extremes of age or body size 3
• Calculating doses of potentially toxic drugs excreted by kidneys 3

Alternative When mGFR Unavailable

• Consider timed urine collections for measured creatinine clearance if mGFR is not available and eGFRcr-cys is thought to be inaccurate 1
• Be aware that creatinine clearance progressively overestimates GFR as kidney function declines, potentially by up to twice the true GFR at 15-20 mL/min 1

Special Populations

• Children: Use pediatric-specific validated equations (Schwartz equation or Full Age Spectrum equation), not adult equations 1, 3
• Glomerular disease patients: No eGFR equation has been specifically validated; consider measured GFR for critical decisions 3

Common Pitfalls to Avoid

• Never rely on serum creatinine alone without using an estimating equation 1, 3
• Do not use race in eGFR computation—the 2021 CKD-EPI equation eliminates this variable 1
• Avoid Cockcroft-Gault equation for routine use, as it overestimates kidney function in CKD stages 3-5 and is less accurate than CKD-EPI 3
• Do not use MDRD equation—it has been superseded by CKD-EPI 2021 and is not valid for eGFR >60 mL/min/1.73 m² 3
• Use the same equation consistently within your geographical region for longitudinal monitoring 1