Yes, it is entirely possible to be born with only one kidney. This condition is formally known as a Congenital Solitary Kidney (CSK), which is often the result of unilateral renal agenesis. While the idea of being born with one kidney may sound serious, many individuals with this condition lead completely normal, healthy lives and may not even discover the absence of the second kidney until later in adulthood. The body’s single kidney adapts remarkably to handle the full workload of two.
The Medical Terminology and Prevalence
The medical term for the complete failure of one kidney to develop in the womb is unilateral renal agenesis. This results in an individual having a Congenital Solitary Kidney. This congenital condition is distinct from an acquired solitary kidney, which is the result of surgical removal due to injury or disease later in life.
Unilateral renal agenesis is estimated to occur in approximately 1 in 1,000 to 2,000 live births, making it a relatively uncommon, yet not extremely rare, congenital anomaly. The condition where both kidneys fail to develop, known as bilateral renal agenesis, is much less common and is typically fatal shortly after birth due to associated lung underdevelopment.
How the Condition Develops During Pregnancy
The development of the kidneys in a fetus is a complex process that begins early in the first trimester. Kidney formation relies on a reciprocal communication between two embryonic structures: the ureteric bud and the metanephric blastema. The ureteric bud, which sprouts from the mesonephric duct, must penetrate and interact with the metanephric blastema.
Renal agenesis occurs when this delicate interaction fails to happen on one side of the body, usually around the fifth week of gestation. If the ureteric bud either fails to emerge or does not properly connect with the surrounding tissue, the metanephric blastema does not receive the signal to form a kidney. Without the necessary signals, the tissue that would have formed the kidney dissolves through a natural process called apoptosis.
The cause is often sporadic, but genetic factors are known to be involved in some cases. Mutations in certain genes, such as RET or GREB1L, have been linked to the failure of development. External factors, including maternal diabetes or the use of specific medications during the first trimester, are also considered potential influences on the developing kidney structures.
Diagnosis and Ongoing Monitoring
The presence of a solitary kidney is often first identified before birth during a routine prenatal ultrasound scan. This imaging test may show an empty renal fossa where one kidney should be located, leading to a suspected diagnosis. Postnatal confirmation typically involves a follow-up renal ultrasound to verify the absence of the kidney and to ensure the remaining kidney is structurally normal and properly positioned.
If not detected prenatally, the condition is frequently an incidental finding later in life when the abdomen is imaged for an unrelated health concern. Lifelong monitoring is recommended, including annual medical check-ups to monitor blood pressure and perform urine tests for protein, a sign of potential kidney strain.
Routine blood tests calculate the estimated Glomerular Filtration Rate (eGFR), measuring how effectively the kidney filters waste from the blood. Renal ultrasounds may also be performed every one to two years to assess the size and structure of the single kidney. This regular surveillance detects early signs of complications like hypertension or proteinuria.
Living Well with a Single Kidney
The remaining kidney compensates for the absence of its pair by undergoing an adaptation process called compensatory hypertrophy. This involves the single kidney physically growing larger and its nephrons, the filtering units, increasing their activity to handle the body’s filtration needs. This increased workload results in a state known as hyperfiltration, where the kidney filters a greater volume of blood.
While this compensatory mechanism is effective for maintaining normal kidney function, the long-term, sustained pressure can increase the risk of complications. Over many decades, chronic hyperfiltration can lead to a low risk of developing proteinuria (protein leakage in the urine) or mild chronic kidney disease. Studies suggest that a small percentage of individuals may develop hypertension or kidney dysfunction by early adulthood.
Individuals with a single kidney are advised to adopt specific lifestyle measures. Maintaining a healthy blood pressure is important, as is following a balanced diet that is moderate in protein and low in sodium, ideally less than 2,300 mg per day. Avoiding excessive use of non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen is also recommended, as these medications can reduce blood flow to the kidney.
Staying well-hydrated is encouraged. While participation in most physical activities is safe, caution is advised for high-impact contact sports. Protective gear is often recommended in sports like football or hockey to minimize the risk of injury to the single organ.