What is the estimated Glomerular Filtration Rate (GFR) for individuals of different ages?

Estimated Glomerular Filtration Rate (GFR) Across Different Age Groups

The estimated GFR varies significantly across age groups, with normal values typically declining with advancing age, and the most accurate estimation requires using age-appropriate equations such as the CKD-EPI equation for adults, with specific considerations for elderly patients where BIS1 or FAS equations may be more appropriate. 1, 2

Normal GFR Values by Age Group

• Children and Adolescents (>2 years):

  • Normal eGFR: ≥90 mL/min/1.73 m² 1
  • Values <90 mL/min/1.73 m² should be flagged as "low" in this age group

• Adults (18-70 years):

  • Stage 1 CKD: ≥90 mL/min/1.73 m² (with evidence of kidney damage)
  • Stage 2 CKD: 60-89 mL/min/1.73 m² (with evidence of kidney damage)
  • Stage 3a CKD: 45-59 mL/min/1.73 m²
  • Stage 3b CKD: 30-44 mL/min/1.73 m²
  • Stage 4 CKD: 15-29 mL/min/1.73 m²
  • Stage 5 CKD: <15 mL/min/1.73 m² 2

• Older Adults (>70 years):

  • Median eGFR typically 10-15 mL/min/1.73 m² lower than younger adults
  • Studies show median values around 53-57 mL/min/1.73 m² in this population 3, 4

GFR Estimation Equations

For Adults (18-70 years):

The CKD-EPI equation is currently recommended as the most accurate for adults:

CKD-EPI equation:

• eGFR (mL/min/1.73 m²) = 186 × [SCr (mg/dL)]^-1.154 × [age (years)]^-0.203 × [0.742 if female] × [1.21 if African American] 1

This equation has been updated to a race-free version in 2021, which is now preferred 1.

For Elderly (>70 years):

Several equations may be more accurate:

1. BIS1 equation (Berlin Initiative Study):

   • Shows better accuracy in patients >70 years 4
   • Estimates lower GFR values than CKD-EPI in this population

2. FAS equation (Full Age Spectrum):

   • Provides continuity across age transitions
   • Less biased in older adults compared to CKD-EPI 5

For Children:

• Modified Schwartz equation is typically used
• For infants and small children, enzymatic creatinine assays are recommended over Jaffe methods due to higher relative contribution of non-creatinine chromogens 1

Age-Related GFR Decline

• GFR typically peaks in early adulthood (around age 20-30) at approximately 120-130 mL/min/1.73 m²
• After age 30-40, GFR declines by approximately 0.75-1 mL/min/1.73 m² per year 3
• By age 80, median GFR is typically around 50-60 mL/min/1.73 m² in healthy individuals 4

Clinical Considerations

• Elderly patients: CKD-EPI and MDRD equations may overestimate GFR in the elderly (median overestimation of 1.7-3.5 mL/min/1.73 m²) 3
• High GFR ranges: MDRD equation tends to underestimate GFR at higher values (>60 mL/min/1.73 m²) 6
• Accuracy limitations: Even the best equations achieve only 80-87% accuracy (defined as estimates within 30% of measured GFR) 3

Important Caveats

1. Serum creatinine alone is inadequate for GFR estimation, particularly in elderly patients, those with reduced muscle mass, or malnutrition 1

2. Laboratory standardization is crucial:

   • Laboratories should use creatinine assays calibrated to international standard reference materials
   • Report eGFR alongside filtration marker concentrations 1

3. Special populations require consideration:

   • Obesity: Both CKD-EPI and MDRD may be less reliable 1
   • Transgender individuals: Limited data on appropriate equations 1

4. Clinical context matters:

   • For drug dosing in patients with severe kidney impairment or when administering potentially toxic drugs, measured GFR using clearance methods may be necessary 1

The most accurate assessment of kidney function requires consideration of both GFR and evidence of kidney damage (such as albuminuria), particularly for diagnosing early stages of CKD 2.