Is Glomerular Filtration Rate (GFR) related to age?

Relationship Between Glomerular Filtration Rate (GFR) and Age

Yes, GFR is definitively related to age, with normal GFR declining progressively with advancing age even in healthy individuals. 1

Normal GFR and Age-Related Changes

• Normal GFR in young adults is approximately 120-130 mL/min per 1.73 m² and begins to decline with age 1
• GFR remains relatively constant until approximately age 40, then begins to steadily decline at a rate of approximately 1 mL/min/1.73 m² per year 2, 3
• By age 70, more than 40 mL/min/1.73 m² of GFR may be lost compared to young adulthood 3
• Approximately 17% of persons older than 60 years of age have an estimated GFR less than 60 mL/min per 1.73 m² 1

Clinical Implications of Age-Related GFR Decline

• Although age-related decline in GFR has historically been considered part of normal aging, decreased GFR in the elderly is an independent predictor of adverse outcomes including death and cardiovascular disease 1
• Age-related GFR decline requires adjustment in drug dosages, just as in other patients with chronic kidney disease 1
• The definition of chronic kidney disease is the same regardless of age, despite the natural decline in GFR with aging 1

Measuring GFR in Different Age Groups

• Serum creatinine alone should not be used to assess kidney function, particularly in the elderly 1
• In the elderly, serum creatinine concentration does not accurately reflect the age-related decline in GFR due to concomitant age-related decline in muscle mass that reduces creatinine generation 1
• For example, a serum creatinine level of 1.2 mg/dL may be associated with a creatinine clearance of 110 mL/min in a young athlete but only 40 mL/min in an elderly woman 1

Estimating GFR Across Age Groups

• GFR estimation equations such as the MDRD study equation and Cockcroft-Gault formula incorporate age as a variable to account for age-related changes in kidney function 1
• These equations take into account serum creatinine concentration along with age, sex, race, and sometimes body size 1
• The Full Age Spectrum (FAS) equation may better model the natural decline of renal function with aging by incorporating a quadratic term for age 4

Structural Changes in the Kidney with Age

• Aging is associated with significant structural changes in the kidney, including decreased kidney cortical volume and increased nephrosclerosis 5
• Nephrosclerosis (characterized by glomerulosclerosis, tubular atrophy, interstitial fibrosis, and arteriosclerosis) increases with age 5, 6
• The decline in nephron number with age is accompanied by a comparable reduction in whole-kidney GFR, though single-nephron GFR remains relatively constant with healthy aging 5

Factors Affecting Age-Related GFR Decline

• Systolic blood pressure is strongly associated with faster decline of eGFR with age 3
• Other factors associated with accelerated GFR decline include albuminuria, left ventricular dysfunction, and elevated white blood cell count 3
• Diastolic blood pressure, serum uric acid, and serum albumin have been associated with slower GFR decline in some analyses 3

Understanding the relationship between GFR and age is crucial for proper interpretation of kidney function tests and appropriate management of patients across the lifespan.