A person can live a completely healthy, normal life with only one kidney. This condition is medically termed monorenal status or a solitary kidney. The remaining organ has a remarkable ability to increase its function and capacity. The single kidney can handle the body’s full waste filtration and fluid balance needs, providing up to 75% of the function normally performed by two kidneys. Overall health and life expectancy are typically not affected.
Common Reasons for Having a Single Kidney
A person might have a solitary kidney for one of three main reasons. The most common cause is the surgical removal of a kidney (nephrectomy), often performed to treat cancer, severe injury, or other diseases. Another frequent reason is kidney donation, where an individual gives one of their healthy kidneys for transplantation. The third category includes congenital conditions, such as renal agenesis (born with only one kidney) or renal dysplasia (born with two kidneys where only one is functional).
The long-term health prognosis depends heavily on the reason the second kidney was lost. Donors generally have the most favorable outcomes because their remaining kidney was healthy initially. Individuals who lost a kidney due to systemic disease, such as cancer or severe infection, may have a less predictable outcome. Those born with a single kidney, particularly due to dysplasia, may have a slightly elevated risk of mild function loss later in adulthood.
How the Remaining Kidney Compensates
The remaining kidney compensates for the loss of its partner through two primary physiological mechanisms. The first is compensatory hypertrophy, which is the physical enlargement of the remaining kidney. This growth affects the filtering units (glomeruli) and the associated tubules, increasing the overall size and weight of the organ. This structural change allows the single organ to accommodate a greater workload.
The second mechanism is glomerular hyperfiltration, an increased rate of blood filtering at the level of the individual nephron. The remaining nephrons increase their single nephron glomerular filtration rate (SNGFR) to maintain the body’s total filtration rate within a near-normal range. This adaptive hyperfiltration is driven by increased blood flow and pressure within the glomeruli. While initially beneficial, this process requires the single kidney to work at a higher, sustained capacity.
Long-Term Monitoring and Potential Health Risks
Due to the increased workload on the solitary organ, long-term monitoring is necessary to ensure kidney health. Regular check-ups with a healthcare professional, such as a nephrologist, are important for vigilance against potential complications. Monitoring involves specific diagnostic tests to assess the kidney’s filtering capacity and overall function.
One of the most important tests is the Glomerular Filtration Rate (GFR), which estimates how quickly the kidney filters waste from the blood. A blood test is also performed to check for protein in the urine (proteinuria or albuminuria). The presence of excess protein indicates that the kidney’s filtering barrier is stressed or damaged.
A primary long-term concern is the development of high blood pressure (hypertension), which the kidneys naturally help regulate. Hypertension can damage the delicate blood vessels within the kidney, creating a cycle that further impairs filtration. Individuals with a solitary kidney are advised to maintain their blood pressure below 130/80 mmHg. The sustained hyperfiltration can also lead to a slightly increased risk of developing Chronic Kidney Disease (CKD) later in life.
Daily Life and Protective Measures
Protecting the single kidney through practical, daily measures is a primary focus for individuals with monorenal status. Consistent fluid intake is important for maintaining hydration, which supports efficient waste filtration. While highly restrictive diets are unnecessary, a general low-sodium diet is beneficial because high sodium intake contributes to high blood pressure and fluid retention, straining the kidney.
A strong warning is issued against the use of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), such as ibuprofen and naproxen, unless approved by a doctor. NSAIDs can reduce blood flow to the kidney and cause acute injury by blocking natural chemicals that dilate renal blood vessels. All medications should be reviewed with a health professional aware of the solitary kidney status.
When considering physical activity, a common concern is participation in contact sports, such as football or boxing. Although the actual risk of a catastrophic kidney injury is extremely low, any injury to the sole kidney would be severe. Therefore, protective gear or avoidance of high-impact activities like high-risk cycling or equestrian sports are sensible protective measures. Maintaining a healthy body weight and avoiding smoking further supports the long-term health of the remaining kidney.