Understanding Glomerular Filtration Rate (GFR)
Glomerular Filtration Rate (GFR) measures how many milliliters of blood your kidneys' microscopic nephrons clean per minute, normalized to an average adult body surface area of 1.73 m² (mL/min/1.73m²). Healthy adult values typically range between 90 and 120 mL/min/1.73m². As part of the natural aging process, GFR declines by approximately 0.8 to 1.0 mL/min/year past the age of 40.
CKD-EPI 2021 Refined Standard
Co-developed by the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) Task Force and published in The New England Journal of Medicine. This standard entirely eliminated race modifiers from clinical eGFR assessment, achieving validated equity and diagnostic precision.
Serum Creatinine & Filtration
Creatinine is a metabolic waste byproduct generated by continuous phosphocreatine breakdown in skeletal muscle. Because kidneys clear creatinine almost entirely through passive glomerular filtration, elevated serum creatinine reflects compromised clearance.
Chronic Kidney Disease (CKD) Stages (KDIGO Guidelines)
- Stage 1 (≥ 90 mL/min/1.73m²): Normal kidney filtration rate. Proteinuria (urine albumin) should be checked to rule out structural injury.
- Stage 2 (60 - 89 mL/min/1.73m²): Mild decrease. Common in elderly populations without intrinsic nephropathy.
- Stage 3a (45 - 59 mL/min/1.73m²): Mild-to-moderate functional loss. Medical review of nephrotoxic medications is advised.
- Stage 3b (30 - 44 mL/min/1.73m²): Moderate-to-severe functional impairment. Active clinical monitoring of blood pressure, anemia, and bone minerals.
- Stage 4 (15 - 29 mL/min/1.73m²): Severe kidney impairment. Planning for renal replacement therapy (dialysis or kidney transplant).
- Stage 5 (< 15 mL/min/1.73m²): End-stage renal disease (ESRD). Dialysis or kidney transplantation required.