eGFR (cystatin C)

Estimated Glomerular Filtration Rate (eGFR, cystatin-C-based) is a measure of kidney function that uses cystatin C—a protein produced at a relatively constant rate by all nucleated cells—along with age and sex. Unlike creatinine, cystatin C is not influenced by muscle mass, making it especially useful in people with unusually high or low muscle mass, the elderly, or those with borderline creatinine-based eGFR values. It is calculated using the CKD-EPI 2012 cystatin C equation. eGFR is reported on the same scale (mL/min/1.73m²), and CKD stages use the same cutoffs (e.g., Stage 3 <60). Values ≥90 are generally ideal, while sustained values below 60 indicate reduced kidney function and warrant medical follow-up.