Why can some people live with one kidney and others require a kidney transplant?

Living with One Kidney vs. Requiring Kidney Transplant

People can live with one kidney when they have one healthy, functioning kidney that can adequately filter blood and maintain homeostasis, whereas kidney transplant is required when both kidneys have failed or when a solitary kidney has lost sufficient function to sustain life.

Understanding Solitary Kidney Function

Physiologic Adaptation

• A single healthy kidney undergoes compensatory hyperfiltration and increased glomerular pressure to maintain adequate renal function 1
• The remaining kidney can typically maintain normal or near-normal kidney function through these adaptive mechanisms 1
• Living kidney donors, trauma patients, and those with nephrectomy for renal malignancies can live normal lives with appropriate monitoring 1

When One Kidney Is Sufficient

People successfully live with one kidney in these scenarios:

• Living kidney donors who donate a healthy kidney while retaining a normal functioning kidney 2
• Individuals who lose one kidney to trauma or surgical removal for cancer, provided the remaining kidney is healthy 1
• The solitary kidney must have adequate baseline function and no significant underlying disease 1

When Kidney Transplant Becomes Necessary

End-Stage Kidney Disease

Kidney transplant is required when kidney function deteriorates to the point where it cannot sustain life, regardless of whether one or both kidneys are present 3, 4

Key indicators for transplant need:

• GFR ≤30 ml/min with progressive decline 2
• Dialysis requirement for ≥8 weeks 2
• Kidney biopsy showing >30% glomerulosclerosis and/or 30% fibrosis 2
• Metabolic kidney diseases (hyperoxaluria, atypical hemolytic uremic syndrome) 2

Failed Kidney Transplant Recipients

• Patients with failing kidney allografts have higher mortality and hospitalization rates compared to those with deteriorating native kidneys 2
• These patients may require repeat transplantation or return to dialysis 2
• Immunosuppression management becomes critical to balance sensitization risk against infection and malignancy 2

Critical Distinction: Function vs. Number

The number of kidneys is less important than their functional capacity. The key factors determining whether someone needs a transplant include:

Functional Criteria

• Total kidney function (measured by GFR) rather than kidney number determines transplant need 2, 5
• One healthy kidney can provide sufficient function (typically 60-80% of two-kidney function) 1
• Two diseased kidneys with combined GFR <15 ml/min require transplant, just as one diseased kidney with GFR <15 ml/min would 2

Disease Progression Factors

• Underlying kidney disease (diabetes, hypertension, glomerulonephritis) determines progression to transplant need 6, 3
• Genetic conditions and preexisting glomerular pathologies can worsen outcomes in solitary kidney 1
• Persons with solitary kidney may develop progressive CKD if they have additional risk factors like diabetes, hypertension, or obesity 1

Survival and Quality of Life Outcomes

Benefits of Transplantation

• Kidney transplantation provides significant survival, cost, and quality-of-life benefits over dialysis 4, 7
• Most studies found significantly lower mortality associated with transplantation, with relative benefits increasing over time 7
• Quality of life is significantly and substantially better among transplant recipients compared to dialysis patients 7

Living with One Kidney

• Living kidney donors and those with acquired solitary kidney can maintain normal life expectancy with proper management 1
• Recommended lifestyle modifications include avoiding excessive protein intake (>1 g/kg/day), limiting sodium (<4 g/day), maintaining BMI <30 kg/m², and managing CKD risk factors 1

Common Pitfalls to Avoid

• Do not assume that having one kidney automatically means transplant is needed—function matters more than number 1
• Avoid excessive dietary protein and sodium in persons with solitary kidney, as this can accelerate decline 1
• Monitor persons with solitary kidney regularly for development of proteinuria, hypertension, and declining GFR 1
• In failed transplant recipients, avoid abrupt cessation of immunosuppression as this increases sensitization and reduces chances of successful repeat transplantation 2