Estimating Glomerular Filtration Rate (GFR) in Clinical Practice

Introduction to eGFR Calculation

The National Kidney Foundation recommends using a validated GFR estimating equation, such as CKD-EPI 2021, with serum creatinine calibrated to international reference standards, to account for differences in creatinine reference ranges by incorporating age, sex, and body surface area 1, 2

Clinical laboratories must measure serum creatinine using assays calibrated to isotope-dilution mass spectrometry (IDMS) reference methodology, as recommended by the American Journal of Kidney Diseases 1, 2
The American Journal of Kidney Diseases suggests that creatinine assays should be traceable to international standard reference materials 1
Values less than 1 mg/dL should be reported to two decimal places (hundredths), according to the American Journal of Kidney Diseases 1
Laboratories must adjust prediction equations to account for differences in creatinine calibration between their assay and the one used to develop the equation, as stated in the American Journal of Kidney Diseases 1

The 2021 CKD-EPI equation without race is the current recommended standard for adults, as suggested by the American Journal of Kidney Diseases 4, 3
For initial assessment in adults, the American Journal of Kidney Diseases recommends using creatinine-based eGFR (eGFRcr) 2, 3
For confirmation when eGFRcr is 45-59 mL/min/1.73 m² without other markers of kidney damage, the American Journal of Kidney Diseases suggests adding cystatin C to calculate combined eGFRcr-cys 2, 5

The American Journal of Kidney Diseases recommends considering cystatin C-based or combined creatinine-cystatin C equations when there are extremes of muscle mass, body weight, or composition, advanced cirrhosis, cancer, or dietary factors affecting creatinine 3, 6
Measured GFR (mGFR) using exogenous markers should be considered when precise GFR measurement is critical for clinical decision-making, as stated in Kidney International 8, 9, 10

Clinicians should request that their laboratory automatically reports eGFR using CKD-EPI 2021, as recommended by the American Journal of Kidney Diseases 4, 3
The American Journal of Kidney Diseases suggests using the same equation consistently within a geographical region 3
For adults without conditions affecting creatinine, eGFRcr is sufficient for initial evaluation, according to the American Journal of Kidney Diseases 3
The American Journal of Kidney Diseases recommends adding cystatin C for confirmation in borderline cases (eGFR 45-59) without albuminuria 2, 5