Renal Agenesis: When a Kidney Does Not Form Before Birth

Perhaps a routine scan during pregnancy, or an imaging test done for something else entirely, brought up a sentence you did not expect: only one kidney can be seen. It is unsettling to hear, and the first question is usually the same — what does this mean for daily life?

Renal agenesis is a condition present from birth in which one kidney or, rarely, both kidneys do not form. Many people with one functioning kidney remain well with appropriate monitoring, while bilateral renal agenesis requires specialized care before and after birth.

Overview: What Is Renal Agenesis?

Renal agenesis is present from birth, meaning it develops before a baby is born, and it means one or both kidneys never formed. The kidneys normally filter waste and excess fluid from the blood, help regulate blood pressure, support healthy bones, and contribute to red blood cell production. When one kidney is absent, the other kidney may enlarge and take on the work of both kidneys.

Doctors talk about two forms. Unilateral renal agenesis means one kidney is missing. It may be discovered during a prenatal ultrasound, an examination for another health concern, or later in life when imaging is performed for an unrelated reason. Bilateral renal agenesis means both kidneys are absent. This is much less common and is a serious developmental condition that requires care from a specialist team.

Renal agenesis belongs to a broader group of conditions called congenital anomalies of the kidneys and urinary tract. It is different from a kidney that formed but later lost function because of disease, injury, or surgery. It is also different from a small or scarred kidney, so imaging is needed to confirm the diagnosis.

How Renal Agenesis Can Affect Health

People with unilateral renal agenesis often have no symptoms. A healthy remaining kidney can usually provide enough filtering capacity for everyday life. Some individuals do not learn they have one kidney until adulthood, including during imaging for abdominal pain, pregnancy care, or a routine medical evaluation.

Even if you feel perfectly well, a single working kidney is worth keeping an eye on. Over many years, some people may develop high blood pressure, protein in the urine, or a reduction in kidney function. These changes are not inevitable, but regular monitoring can identify concerns early and help protect long-term kidney health.

Some children and adults with renal agenesis have differences elsewhere in the urinary tract, such as reflux of urine toward the kidney, narrowing of a urinary passage, or an absent or unusually positioned ureter. Differences in reproductive organs can also occur because the urinary and reproductive systems develop close together before birth. The need for further assessment depends on the individual findings and symptoms.

Symptoms and Signs

Unilateral renal agenesis commonly causes no obvious symptoms. If the remaining kidney and urinary tract are healthy, a child may grow and develop normally. For this reason, the condition is often found incidentally rather than because it causes pain or illness.

Symptoms, when present, may relate to an associated urinary tract condition rather than the absent kidney itself. These can include recurrent urinary tract infections, fever with a urinary infection in a young child, pain in the side or back, blood in the urine, difficulty passing urine, or new urinary leakage. Swelling, persistent tiredness, or changes in urine output should also be assessed, although they have many possible causes.

During pregnancy, an ultrasound may show that one kidney cannot be seen or that the amount of amniotic fluid is lower than expected. Low amniotic fluid can occur in bilateral renal agenesis because fetal urine contributes substantially to amniotic fluid later in pregnancy. A fetal medicine specialist can explain what the scan findings mean and arrange confirmatory evaluation.

Causes and Risk Factors

Renal agenesis occurs when normal kidney development is interrupted early in pregnancy. In most cases, there is no single identifiable cause, and it is not the result of an activity, food, exercise, or ordinary stress during pregnancy. If you are a parent hearing this news, please know it is not something you caused.

Genetic factors may contribute in some families. Renal agenesis can occur on its own or as part of a genetic syndrome that affects other organs. A family history of congenital kidney, urinary tract, or reproductive-system differences may lead a clinician to recommend genetic counseling or testing. However, many people with unilateral renal agenesis have no known family history.

Healthcare professionals also review pregnancy and family history carefully, including maternal health conditions, medicines, and possible exposures. This review helps guide care but does not always establish a cause. For people considering a future pregnancy, pre-pregnancy counseling can provide individualized information about screening and recurrence considerations.

Diagnosis and Follow-Up Testing

Ultrasound is usually the first test used to evaluate possible renal agenesis. Before birth, detailed fetal ultrasound can assess whether kidneys are visible, examine the bladder and urinary tract, and measure amniotic fluid. After birth or later in life, abdominal and renal ultrasound can confirm whether a kidney is absent and evaluate the size and appearance of the remaining kidney.

Sometimes additional tests are needed because a kidney may be difficult to see, unusually located, very small, or poorly functioning rather than truly absent. Depending on the situation, clinicians may use magnetic resonance imaging, specialized nuclear medicine scans, or other imaging studies. These tests can also help identify urinary blockage or urine reflux when there is a clinical reason to look for them.

Blood tests can measure kidney filtration, while a urine test can check for protein, blood, or signs of infection. Blood pressure measurement is a central part of follow-up for children and adults with one kidney. Clinicians may also recommend assessment by pediatric nephrology, adult nephrology, or urology, particularly when kidney function is reduced, urinary tract differences are found, or infections recur.

Treatment and Everyday Kidney Protection

There is no treatment that can create a kidney that did not develop. Care for unilateral renal agenesis focuses on protecting the remaining kidney, detecting related urinary tract problems, and supporting normal daily life. Most people do not need treatment solely because they have one kidney, but they do benefit from a personalized follow-up plan.

Monitoring commonly includes periodic blood pressure checks, urine testing for protein, and blood tests for kidney function when advised by a clinician. The frequency depends on age, kidney test results, and whether other urinary tract differences are present. Urinary tract infections should be assessed promptly, especially in infants and young children, because recurrent infections may require further investigation.

Day to day, the basics matter: drink enough fluid for your own needs, eat a balanced diet, keep to a healthy weight, stay away from tobacco, and keep conditions like diabetes or high blood pressure under control. People should discuss frequent use of anti-inflammatory pain medicines, supplements, or herbal products with a clinician, as some substances can affect kidney function. Contact sports are not automatically prohibited, but the decision should be individualized after discussing the activity, protective equipment, and personal risk with a healthcare professional.

Bilateral renal agenesis requires highly specialized care. When identified during pregnancy, families are typically supported by maternal-fetal medicine, neonatology, pediatric nephrology, and other relevant specialists. The care plan is individualized and includes clear counseling about the baby’s health needs and available supportive options.

Living With One Kidney: Practical Planning

Having one kidney does not usually prevent a person from attending school, working, traveling, exercising, or having a family. Do tell any doctor treating you that you have one kidney before you start a new medicine, have a scan with contrast dye, or go for major surgery. Keeping a record of imaging and kidney test results may also make future care easier.

Children with unilateral renal agenesis should continue routine childhood care, including vaccinations and growth monitoring. Parents and caregivers can encourage regular fluid intake, healthy meals, and prompt reporting of urinary symptoms. As children grow older, involving them in understanding their condition can help them take an active role in appointments and healthy habits.

For adults, pregnancy is often possible with a solitary kidney, but pre-pregnancy or early pregnancy review is sensible. Monitoring blood pressure and kidney function may be recommended more closely during pregnancy. Acıbadem Health Point’s multidisciplinary specialists and JCI-accredited hospitals provide diagnostic assessment and care planning for international patients with congenital kidney conditions.

When to Seek Medical Care

Medical review is appropriate if a prenatal scan suggests a kidney difference, if a child has repeated urinary tract infections, or if a person is told incidentally that they may have one kidney. A clinician can arrange suitable imaging and explain whether the finding is renal agenesis or another kidney condition.

Prompt medical attention is important for fever with urinary symptoms in an infant or young child, severe pain in the side or back, visible blood in the urine, inability to pass urine, marked reduction in urine output, or swelling of the face, hands, or legs. These symptoms do not necessarily mean kidney failure, but they should be evaluated without delay.

If you know you have one kidney, keep your follow-up appointments even on the days you feel completely fine. Early identification of high blood pressure, urine protein, or changes in kidney function gives the healthcare team an opportunity to recommend appropriate next steps.

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