What is a solitary functioning kidney?
Most people have two kidneys. Some children, however, have only one kidney that works. This is called a solitary functioning kidney. The main causes are:
- A kidney that never formed (renal agenesis). The kidney does not develop before birth. Renal agenesis occurs in about 1 in 2,000 babies.
- Multicystic dysplastic kidney. The kidney is there but is filled with cysts and does not work.
- Removal of a kidney (nephrectomy). For example, because of a tumor or a blockage that destroyed the kidney.
It is slightly more common in boys. The diagnosis is confirmed by ultrasound.
How the healthy kidney adapts
To do the work alone, the single kidney grows larger. This is called compensatory hypertrophy, and it can start before birth, from about the 20th week of pregnancy. The kidney filters more, and total kidney function stays close to the level of two kidneys.
This adaptation has a cost: the kidney works under extra load for many years. Children with a single kidney therefore have a higher risk over time of high blood pressure, protein in the urine and reduced kidney function. In a study of 407 children, 37% had at least one of these signs. The risk rises with age, especially during puberty. It is higher still if the single kidney does not grow as expected or has another abnormality.
Other abnormalities
About one in three children also has another birth difference in the single kidney or urinary tract. The most common are vesicoureteral reflux (in about 20% of children) and UPJ obstruction (in about 5%).
Not every child needs a voiding cystourethrogram. It is usually done if ultrasound shows a dilated ureter or suggests severe reflux, or if the child has had a urinary tract infection.
Follow-up
A child with a single kidney needs lifelong follow-up. International recommendations for a kidney missing from birth are:
| Check | When |
|---|---|
| Blood pressure | Every year |
| Urine test (protein) | Every year |
| Kidney function blood test (creatinine, eGFR) | Every 5 years until puberty, then every 2 years |
| Kidney ultrasound | At 1 year, then every 5 years |
If blood pressure has been high or kidney function has dropped, 24-hour blood pressure monitoring is added and the child is followed together with a pediatric nephrologist. For children whose kidney was removed by surgery, the treating team sets an individual follow-up plan.
Looking ahead for girls: women with a single kidney have about a 2.5 times higher risk of high blood pressure and preeclampsia in pregnancy, so the doctor should always be told during pregnancy.
Daily life and sports
- Diet: no special diet is needed. Using little salt, keeping a healthy weight and drinking enough fluids are enough.
- Medicines: tell every doctor that your child has one kidney. Medicines that can harm the kidneys should be used as little as possible.
- Sports: for a long time, children with one kidney were kept out of contact sports. Current data show that kidney injury during sports is very rare, and none of the reported injuries led to loss of the kidney. Among children, cycling is the most common cause of sports-related kidney injury. Physical activity is therefore encouraged. Opinions are not fully uniform: the American Academy of Pediatrics advises individual assessment for contact and collision sports and notes that protective gear may reduce the risk enough to allow most sports. Discuss your child’s chosen sport with the doctor.
When to see a doctor
Do not skip the planned checks. In addition, do not wait for the next planned visit in these situations:
- a fever of 38 °C or higher, especially without another obvious cause,
- blood in the urine or pain after a hard blow to the abdomen, side or back,
- repeatedly high blood pressure readings at home.
When to seek urgent care
If any of the following is present, do not wait for a routine appointment: call the doctor or go to the nearest emergency department.
- Fever of 38 °C or higher in a child with a solitary kidney (possible urinary tract infection)
- Blood in the urine or pain after a hard blow to the abdomen, side or back
Call your local emergency number (112 in Europe, 911 in North America)
Note for pediatricians and family doctors
The main congenital causes of a solitary functioning kidney are unilateral renal agenesis and multicystic dysplastic kidney; the acquired form follows nephrectomy (for example for Wilms tumor or obstructive uropathy). Compensatory hypertrophy can begin as early as 20 weeks of gestation and is defined as a kidney length more than 2 SD above the reference for age. Its absence, and additional CAKUT (in about one in three children; VUR in about 20%, UPJ obstruction in about 5%), are associated with a worse prognosis. In the KIMONO cohort (n = 407), 37% of children had kidney injury (hypertension, proteinuria, reduced GFR or need for renoprotective medication), and risk rises with age and during puberty. Suggested follow-up for the congenital form: yearly office blood pressure and urinalysis; yearly ambulatory BP monitoring from age 5 in children with current or previous hypertension or CKD (and to be considered in all children from that age); eGFR every 5 years until puberty and every 2 years thereafter; ultrasound at 1 year and then every 5 years. VCUG is a second-line test, used when high-grade VUR is suspected on ultrasound, the ureter is dilated, or a UTI occurs. Refer to pediatric nephrology if eGFR falls by more than 5 ml/min/1.73 m² over 2 years or below 90 ml/min/1.73 m²; when kidney injury is present, ACE inhibitors are first-line. Avoid combining RAAS inhibitors with NSAIDs and minimize other nephrotoxic drugs.
What happens at the visit?
- All prenatal and postnatal ultrasound results are reviewed together: kidney size, growth, dilation and the ureter are assessed.
- We measure blood pressure, test the urine, and check kidney function in the blood when needed.
- We set up an individual follow-up schedule, give advice on sports and medicines, and plan joint care with a pediatric nephrologist when needed.
Frequently asked questions
Can my child play soccer or do wrestling?
In most cases, yes. Kidney injury during sports is very rare, and the benefits of physical activity outweigh this small risk. For contact and collision sports the decision is individual, and protective gear may reduce the risk. Discuss the specific sport with your doctor.
Does my child need a special diet?
No. Avoiding too much salt, preventing excess weight and drinking enough fluids are recommended. Restricting protein has not been shown to help children.
Which medicines need caution?
Tell every doctor that your child has one kidney. Check with the doctor before using medicines that can harm the kidneys, including nonsteroidal anti-inflammatory drugs such as ibuprofen.
Related topics
- Multicystic dysplastic kidneyCystic, non-functioning kidneyCondition
- Vesicoureteral refluxUreteral reflux, VURCondition
- UPJ obstructionNarrowing between the renal pelvis and the ureterCondition
- Kidney and bladder ultrasoundUltrasound scan, sonographyTest
- Obstructive uropathies and antenatal hydronephrosisFor doctors
Sources
- Groen in ’t Woud S et al. Clinical management of children with a congenital solitary functioning kidney: overview and recommendations. Eur Urol Open Sci, 2021.
- Westland R et al. Risk factors for renal injury in children with a solitary functioning kidney. Pediatrics, 2013.
- McArdle Z et al. Physiology and pathophysiology of compensatory adaptations of a solitary functioning kidney. Front Physiol, 2020.
- Rice SG et al. Medical conditions affecting sports participation. Pediatrics, 2008.
- Grinsell MM et al. Single kidney and sports participation: perception versus reality. Pediatrics, 2006.
- NIDDK. Solitary or single-functioning kidney.
This information is for educational purposes and does not replace medical advice. Decisions about your child’s treatment are made with the doctor after an examination.
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