A significant number of people live with a single kidney, a condition referred to as a solitary kidney. This single organ is often able to take over the work normally performed by two, allowing individuals to live well. Having only one kidney falls into two broad categories: those born with a single kidney and those who lose one later in life. Long-term health outcomes are generally positive, though careful monitoring is recommended to protect the remaining organ.
Understanding the Prevalence of a Single Kidney
A solitary kidney is not an uncommon occurrence, resulting from either a developmental issue before birth or the surgical removal of a kidney later in life. The condition is sometimes referred to as a solitary functioning kidney, which includes cases where a person has two organs but only one is working effectively. Estimates suggest that between 1 in 750 and 1 in 1,000 babies are born with a single kidney, a condition known as unilateral renal agenesis. The number of people living with a solitary kidney increases further when factoring in adults who have undergone nephrectomy, the surgical removal of a kidney.
Congenital Causes
A person may be born with a solitary kidney if the organ failed to develop during gestation, a condition medically termed renal agenesis. Unilateral renal agenesis occurs when the structures that form the kidney do not interact correctly in the early weeks of fetal development. In other cases, the kidney is present but not fully functional, a condition called renal dysplasia. This dysplastic kidney may be small and structurally abnormal, eventually leaving the person with only one working organ.
The single, healthy kidney often undergoes a process called compensatory hypertrophy, where it grows larger and works harder to take on the role of both kidneys. This adaptive process allows the single kidney to achieve a total filtration capacity of up to 75% of what two normal kidneys would provide. While this compensatory mechanism is effective, the single kidney’s nephrons—the microscopic filtering units—are under increased stress, a state known as hyperfiltration. This increased workload is the reason people born with a solitary kidney may face a slightly higher risk of developing health issues like high blood pressure or protein in the urine later in life.
Acquired Causes
The loss of a kidney later in life, resulting in an acquired solitary kidney, most frequently occurs due to a surgical procedure called a nephrectomy. The most common elective reason for a healthy person to have a nephrectomy is to become a living kidney donor. Every year, thousands of people choose to donate one of their kidneys to a family member, friend, or stranger whose own kidneys have failed.
A kidney may also be surgically removed for therapeutic reasons to treat a specific disease or injury. This necessity arises with conditions such as kidney cancer, where the entire organ must be removed to prevent the spread of malignancy. Other non-cancerous conditions, including severe infections, large kidney stones that have caused irreparable damage, or advanced polycystic kidney disease, may also necessitate removal of the affected organ. Finally, severe physical trauma, such as that sustained in a car accident or a significant fall, can damage a kidney beyond repair, making an emergency nephrectomy a life-saving measure.
Long-Term Health and Monitoring
Most individuals with a single healthy kidney, whether congenital or acquired, lead normal, full lifespans. The remaining organ effectively manages the body’s waste filtration, fluid balance, and blood pressure regulation. However, the kidney’s increased workload means that regular, lifelong monitoring is an important part of health maintenance.
Monitoring typically involves periodic blood tests to measure the Glomerular Filtration Rate (GFR), which is the best indicator of how well the kidney is filtering waste. Urine tests are also regularly performed to check for the presence of protein, known as proteinuria, which can be an early sign of stress on the nephrons. Maintaining optimal blood pressure is a specific focus, as hypertension can accelerate damage to the kidney’s delicate blood vessels. Lifestyle recommendations include staying well-hydrated and taking precautions to avoid direct impact injuries, which often means avoiding high-contact sports like football or boxing to protect the lone organ.