How many people are born with 1 kidney?

Having only one kidney, known medically as renal agenesis or unilateral renal agenesis, is a condition present from birth affecting around 1 in 1000 people. It occurs when one of the kidneys fails to develop in utero, resulting in individuals being born with just a single kidney rather than the typical pair. While not ideal, most people born with one kidney are able to live normal, healthy lives with few complications. Here we will explore the prevalence, causes, symptoms, and prognosis for individuals with this condition.

Quick Facts

  • Approximately 1 in 1000 people are born with just one kidney, a condition called renal agenesis
  • Renal agenesis occurs when one kidney fails to develop in utero, usually due to a genetic mutation or error during fetal development
  • Most people with one kidney are asymptomatic and the condition is often discovered incidentally
  • Potential complications include high blood pressure, kidney disease, and decreased kidney function later in life
  • Treatment focuses on managing any symptoms or complications and may include medications for blood pressure control and kidney protection
  • With proper medical care, the prognosis for someone with one kidney is generally good

Prevalence of Unilateral Renal Agenesis

Renal agenesis, also known as unilateral renal agenesis, is estimated to occur in around 1 in 1000 live births. This makes it one of the more common kidney abnormalities present from birth. However, the exact prevalence is difficult to determine for a few reasons:

  • It often goes undiagnosed if no symptoms are present
  • Estimated prevalence ranges in studies from 1 in 500 to 1 in 1300 live births
  • Rates may depend on geographic location and ethnic factors

Based on reviews of multiple studies, a prevalence estimate of around 1 in 1000 live births is reasonable. This means that for every 1000 babies born, one baby will be born with just one kidney. Extrapolating this, tens of thousands of babies are born with unilateral renal agenesis each year worldwide.

Diagnosis Rates

While about 1 in 1000 people are believed to have one kidney from birth, the condition is often not diagnosed right away or potentially ever in some individuals. Studies looking at autopsy results have found higher rates than those looking at medical records. This suggests many cases go undetected, likely because the person was asymptomatic and had no related health problems stemming from their solitary kidney.

Diagnosis rates from studies range from 1.1 to 1.7 per 1000 births when reviewing medical records. However, diagnosis rates rise to 4.5-7.9 per 1000 when looking at autopsy findings. The true prevalence likely falls somewhere in the middle of these ranges.


So why are some babies born with just one kidney? Renal agenesis occurs when one of the kidneys fails to fully form during fetal development in the womb. There are a few possible underlying causes:

  • Genetic mutations – Researchers have identified mutations in several genes that may interfere with normal kidney development. These genetic errors likely account for about 10-40% of cases.
  • Kidney development errors – For unknown reasons, one kidney may simply fail to develop properly, while the other kidney forms normally. This is considered a sporadic developmental error.
  • Fetal teratogens – Exposure to harmful substances (teratogens), such as certain medications or illegal drugs during pregnancy, may impact fetal kidney development resulting in agenesis of one kidney.
  • Reduced blood flow – Compromised blood supply to the developing kidneys may also impair growth of one kidney.

Often, no specific cause can be identified. But some combination of genetic mutations, random developmental errors, teratogens, and compromised blood flow to the kidneys likely underlies most cases.

Unilateral vs. Bilateral Renal Agenesis

With unilateral renal agenesis, only one kidney is missing. The other kidney is usually normal. Unilateral agenesis is much more common than bilateral renal agenesis, where both kidneys fail to form. Bilateral agenesis is incompatible with life and fetuses with the condition do not survive to birth.

Symptoms and Complications

Most people born with just one kidney have no symptoms or complications related to their condition. Their solitary kidney is able to take over the work for the missing one. Blood is filtered and waste removed effectively with overall normal kidney function.

When symptoms do occur, they may include:

  • High blood pressure (hypertension)
  • Blood and protein in the urine (hematuria and proteinuria)
  • Urinary tract infections
  • Prenatal hydronephrosis (swelling of the kidney)

Potential long-term complications include:

  • Chronic kidney disease
  • End-stage kidney failure requiring dialysis or transplant
  • Increased risk for kidney cancer in the solitary kidney

However, most of those born with solitary kidney enjoy normal health and kidney function throughout life with a relatively low risk of serious complications.

No Symptoms in Many Cases

Upwards of 80-85% of people with unilateral renal agenesis report no adverse symptoms and enjoy normal health and kidney function. Many do not even realize they have only one kidney until it is detected incidentally through medical imaging for other reasons.

The solitary kidney present enlarges (hypertrophies) to take on the workload of both kidneys. With no symptoms or health impact, the condition often goes undiagnosed unless abnormalities are noted prenatally on ultrasound or after birth during evaluation of an unrelated condition.


There are several ways in which unilateral renal agenesis may be diagnosed:

  • Prenatal ultrasound – May detect absence of one kidney during routine fetal screening. This accounts for around 50% of diagnoses.
  • Postnatal imaging – Abdominal X-rays, CT scan, MRI, or ultrasound of the urinary tract done for other reasons may reveal the absence of one kidney.
  • Urinary tract infection – Evaluation of a UTI may uncover the underlying condition.
  • Incidental finding – Discovery during surgery or autopsy that only one kidney is present.

Once suspected, doctors will order imaging tests such as an abdominal ultrasound, CT scan, or MRI to confirm one kidney is missing and look at the size and structure of the remaining kidney.

Prenatal vs. Postnatal Diagnosis

Prenatal diagnosis rates have increased with routine fetal ultrasounds during pregnancy. One large study found that prenatal ultrasound detected 55% of unilateral renal agenesis cases, compared to just 16% detected postnatally and 29% found incidentally.

Early diagnosis allows parents and doctors to monitor the solitary kidney growth and prepare for any related complications. However, most cases are still discovered after birth when symptoms appear or during evaluation of unrelated problems.


For those without symptoms or related problems, no treatment may be needed beyond regular monitoring of the solitary kidney with imaging tests. Doctors focus on managing any symptoms or complications that do arise:

  • Blood pressure control – Medications to control high blood pressure (hypertension), which is more common in those with one kidney.
  • Antibiotics – To treat urinary tract infections, which occur more frequently.
  • Kidney protective drugs – Medications that reduce strain on the remaining kidney and slow kidney damage in those with chronic kidney disease.

In most cases, medical management with careful monitoring and control of complications provides good outcomes. Severe kidney disease is rare, and most can avoid dialysis or kidney transplantation.

Kidney Removal

Surgical removal of the solitary kidney is almost never required in those with one kidney present from birth. However, if serious complications like recurrent kidney infections or cancer develop, the kidney may need to be removed. Dialysis would then be required until a donor kidney transplant could be performed.

Outlook and Prognosis

What is the long-term outlook for those born with just one kidney? For the majority of affected individuals, prognosis is excellent:

  • Most have normal kidney function and health without complications related to their condition
  • Studies show around 80-90% have normal glomerular filtration rate (GFR), indicating normal kidney function
  • Hypertension risk only slightly higher compared to the general population
  • Only a minority develop chronic kidney disease later in life

Of course, regular medical care is still recommended to monitor the solitary kidney and manage any related problems should they arise. But overall, people born with unilateral renal agenesis can expect a normal lifespan with good kidney health into old age.

Impact on Life Expectancy

Data suggests that congenital absence of one kidney has minimal impact on life expectancy for most:

  • Overall mortality no different compared to the general population
  • Developing end-stage kidney disease appears only slightly more likely
  • May be some increased cardiovascular risk from higher rates of hypertension

With access to modern medical treatment, the prognosis for longevity is favorable. Of course, those who develop chronic kidney disease later in life have higher mortality and may require dialysis or a kidney transplant.

Key Takeaways

The key points to remember about unilateral renal agenesis include:

  • Approximately 1 in 1000 people are born with only one kidney due to renal agenesis
  • Genetic mutations, developmental errors, or reduced fetal blood flow prevents one kidney from forming
  • Most people with one kidney have no symptoms and normal health and kidney function
  • Potential complications include high blood pressure, kidney infections, and increased kidney disease risk later in life
  • Treatment centers on controlling symptoms and complications when they occur
  • Monitoring and medical management provides good outcomes for the majority
  • Life expectancy is generally normal for those born with solitary kidney


Being born with just one kidney is a relatively common congenital condition, estimated to affect around 1 in 1000 people due to unilateral renal agenesis. While not ideal, the outlook for people born with one kidney is generally quite good. Most will enjoy normal health and kidney function throughout life with minimal complications related to their solitary kidney. With proper medical treatment when needed, the prognosis for longevity and quality of life is favorable.

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