At what percentage of normal function is a kidney considered non-functioning?

At What Percentage is a Kidney Considered Non-Functioning

A kidney is considered non-functioning (kidney failure) when the glomerular filtration rate (GFR) falls below 15 mL/min per 1.73 m², which represents approximately 10-15% of normal kidney function. 1

Definition of Kidney Failure

• Kidney failure is defined as either a GFR less than 15 mL/min per 1.73 m² (which is typically accompanied by signs and symptoms of uremia) or the need to start kidney replacement therapy (dialysis or transplantation) 1
• This represents Stage 5 of Chronic Kidney Disease (CKD) according to the Kidney Disease: Improving Global Outcomes (KDIGO) classification system 1
• Approximately 98% of patients with kidney failure in the United States begin dialysis when their GFR falls below this threshold 1

Classification of Kidney Function

Kidney function is classified into stages based on GFR:

• Normal or High: GFR ≥90 mL/min per 1.73 m² (Stage G1) 1
• Mildly Decreased: GFR 60-89 mL/min per 1.73 m² (Stage G2) 1
• Moderately Decreased:
  • G3a: GFR 45-59 mL/min per 1.73 m² 1
  • G3b: GFR 30-44 mL/min per 1.73 m² 1
• Severely Decreased: GFR 15-29 mL/min per 1.73 m² (Stage G4) 1
• Kidney Failure: GFR <15 mL/min per 1.73 m² (Stage G5) 1

Clinical Manifestations of Kidney Failure

• Clinical symptoms and signs are generally poor predictors of reduced renal function until GFR falls below 15 mL/min/1.73 m² 2
• At GFR <15 mL/min/1.73 m², patients commonly present with:
  • Hypertension
  • Vomiting
  • Pruritus (itching)
  • Peripheral edema
  • Hyperpigmentation
  • Peripheral neuropathy
  • Severe anemia 2

Important Considerations

• The term "kidney failure" is not synonymous with "end-stage renal disease" (ESRD) 1
• ESRD is an administrative term in the United States that indicates a patient is treated with dialysis or transplantation 1
• The classification of ESRD does not include patients with kidney failure who are not treated with dialysis and transplantation 1
• GFR estimation equations may be less accurate in advanced kidney disease, especially in elderly patients and those with diabetic nephropathy 3
• For more accurate assessment in advanced kidney disease, direct measurement methods such as 51Cr-EDTA or inulin clearance may be preferred 4

Age-Related Considerations

• Normal GFR in young adults is approximately 120-130 mL/min per 1.73 m² and declines with age 1
• Renal function declines by approximately 1% per year beyond age 30-40 4
• Despite this age-related decline, the definition of kidney failure remains the same regardless of age (GFR <15 mL/min per 1.73 m²) 1
• Recent evidence suggests that using combined creatinine and cystatin C-based GFR estimation (eGFRcr-cys) provides more accurate risk prediction in older adults than creatinine-based estimates alone 5