Understanding estimated glomerular filtration rate: implications for identifying chronic kidney disease

Area of Science:

• Nephrology
• Clinical Chemistry
• Biomarker Analysis

Background:

• Glomerular filtration rate (GFR) is a key indicator of kidney function.
• Serum creatinine (SCr) and cystatin C are common markers for estimating GFR.
• Accurate GFR estimation is vital for diagnosing and managing kidney diseases.

Purpose of the Study:

• To review new insights into estimated GFR (eGFR) based on theory and validation.
• To examine SCr assay standardization, cystatin C, and longitudinal comparisons with measured GFR.
• To provide guidance on interpreting eGFR in various clinical contexts.

Main Methods:

• Review of existing literature on GFR estimation theories and validation studies.
• Analysis of SCr assay standardization and cystatin C performance.
• Longitudinal comparison of eGFR with measured GFR across different populations.

Main Results:

• SCr-based eGFR estimation differs between healthy individuals and those with chronic kidney disease (CKD).
• Measured GFR declines faster than SCr-based eGFR in populations with normal baseline GFR.
• While elevated SCr is specific for CKD, elevated cystatin C can occur in other conditions. Validation requires refitting equations and appropriate bias assessment methods.

Conclusions:

• SCr should be used as a marker of CKD probability, interpreted within the patient's clinical context.
• Measured GFR or creatinine clearance may be beneficial for high-risk individuals with normal SCr.
• GFR estimating equations are best reserved for patients with diagnosed CKD; standardized assays are needed.