What is the most accurate method for estimating GFR in adults, and how does it compare to creatinine clearance?

The most accurate method for estimating glomerular filtration rate (GFR) in adults is to use the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation based on serum creatinine measurement. Clinical laboratories in the UK are recommended to report an estimated GFR (eGFRcreatinine) using this equation alongside serum creatinine results, employing creatinine assays calibrated to standardised reference material and specific enzymatic methods to ensure accuracy.

Compared to creatinine clearance, eGFRcreatinine using the CKD-EPI equation is preferred for routine clinical use due to better standardisation and less variability. Creatinine clearance requires timed urine collections, which are more cumbersome and prone to collection errors, whereas eGFRcreatinine provides a reliable, convenient estimate from a blood sample.

However, eGFRcreatinine may be less reliable in certain populations such as those with extremes of muscle mass, acute kidney injury, pregnancy, oedematous states, or malnutrition, and has limited validation in some ethnic groups. In cases where highly accurate GFR measurement is needed (e.g., chemotherapy dosing or living kidney donor evaluation), reference standard methods such as inulin clearance or radiolabeled markers (51Cr-EDTA, 125I-iothalamate, iohexol) should be considered.