Renal Scarring

What is renal scarring?

Renal scarring is permanent damage to the tissue of the kidney, in which healthy, working kidney tissue is replaced by fibrous scar tissue that cannot filter blood. The word renal simply means relating to the kidneys. Once a scar has formed, that area of the kidney no longer works, although the rest of the kidney can often continue to function normally.

Renal scarring is most often talked about in children, where it usually follows a kidney infection (pyelonephritis), especially in children who have vesicoureteral reflux. Vesicoureteral reflux is a condition in which urine flows backward from the bladder up toward the kidneys instead of only flowing downward. When scarring develops because of reflux, doctors may call it reflux nephropathy. Nephropathy is a general term for kidney disease.

Adults can also develop renal scarring. In adults it is frequently the end result of long-standing kidney conditions such as repeated infections, blockage of urine flow, high blood pressure, diabetes, or inflammatory diseases of the kidney filters. In these cases doctors may describe the scarring using terms such as glomerulosclerosis (scarring of the tiny filtering units) or interstitial fibrosis (scarring of the supporting tissue between the filters).

A small scar in one kidney often causes no problems at all. Extensive scarring, or scarring in both kidneys, can reduce overall kidney function and may lead to complications such as high blood pressure or, in some cases, chronic kidney disease. In many hospitals, including Acibadem, renal scarring is managed by nephrology, the specialty that deals with kidney disease, often together with urology and pediatrics.

Renal scarring symptoms

Renal scarring symptoms are often absent, particularly when only a small area of one kidney is affected. Many people first learn they have a scar when imaging is done for another reason, or during follow-up after a kidney infection. When symptoms do occur, they usually reflect either the condition that caused the scarring or a reduction in kidney function.

• High blood pressure (hypertension), which may be found on a routine check and may appear years after the scar formed
• Protein in the urine (proteinuria), which is usually detected on a urine test rather than noticed by the patient
• Blood in the urine (hematuria), visible or found only on testing
• Repeated urinary tract infections, with burning when passing urine, urgency, or cloudy urine
• Flank pain, a dull ache in the side or back below the ribs, particularly during infections
• Fever during an active kidney infection
• Swelling of the ankles, feet, or around the eyes if kidney function has declined significantly
• Tiredness, poor appetite, or nausea in more advanced loss of kidney function
• Poor growth in children with extensive scarring in both kidneys

How symptoms present tends to differ by stage. In the early stage, scarring is usually silent. In the intermediate stage, blood pressure may rise or protein may appear in the urine even though the person feels well. In advanced disease, when a large amount of kidney tissue has been lost, the general symptoms of reduced kidney function become more noticeable. Because the early stages are so often symptom-free, doctors rely on follow-up testing rather than on how a person feels.

Causes and risk factors

Renal scarring causes fall into a few broad groups. Understanding the underlying cause matters because it guides both treatment and the effort to prevent further damage.

• Kidney infection (acute pyelonephritis): bacteria reaching the kidney cause inflammation, and as the inflamed tissue heals it can leave a scar. This is the most common cause in children. Delayed or incomplete treatment of the infection is thought to increase the chance of scarring.
• Vesicoureteral reflux: backward flow of urine carries bacteria toward the kidney and can also raise pressure inside it. Higher grades of reflux are associated with a greater likelihood of scarring.
• Obstruction of urine flow: blockage from kidney stones, a narrowing where the kidney joins the ureter, an enlarged prostate, or other structural problems can cause pressure that damages tissue over time.
• Chronic kidney diseases: long-standing diabetes, high blood pressure, and glomerulonephritis (inflammation of the kidney filters) can all gradually replace working tissue with scar.
• Reduced blood supply: narrowing of the arteries to the kidney or a previous kidney infarction (loss of blood flow to part of the kidney) can leave scarred areas.
• Injury or medical treatment: physical trauma to the kidney, previous kidney surgery, or radiation to the area may result in scar tissue.
• Congenital abnormalities: some children are born with kidneys that developed abnormally (renal dysplasia), and these areas may look like scars on imaging even though no infection occurred.

Risk factors that make scarring more likely include being very young at the time of a kidney infection, having more than one kidney infection, having high-grade reflux, a delay of several days before starting antibiotics for a febrile urinary tract infection, bladder or bowel dysfunction such as chronic constipation or infrequent voiding, and any anatomical condition that blocks or slows the flow of urine. In adults, poorly controlled diabetes and high blood pressure are important risk factors for progressive scarring.

Renal scarring diagnosis

Renal scarring diagnosis relies mainly on imaging, supported by blood and urine tests that measure how well the kidneys are working. Doctors usually look for scarring after a child has had a kidney infection, when reflux has been identified, or when unexplained high blood pressure or abnormal urine findings are discovered.

• DMSA renal scan: this is a nuclear medicine test in which a small amount of a tracer called technetium-99m dimercaptosuccinic acid is injected into a vein and taken up by working kidney tissue. Scarred areas do not take up the tracer and appear as gaps on the images. This scan is widely regarded as the most sensitive way to detect renal scars and to compare the function of the two kidneys. Doctors often wait several months after an infection before performing it, so that temporary inflammation is not mistaken for a permanent scar.
• Kidney ultrasound: a painless scan using sound waves that shows kidney size, shape, and outline. It may show a small kidney, a thinned outer layer, or an irregular surface. Ultrasound is less sensitive than a DMSA scan for small scars but is often the first test used.
• Voiding cystourethrogram (VCUG): an X-ray study in which contrast dye is placed in the bladder through a thin tube and images are taken while the bladder fills and empties. It shows whether reflux is present and how severe it is.
• Blood tests: serum creatinine and estimated glomerular filtration rate (eGFR) give an overall measure of kidney function. Electrolytes and blood counts may also be checked.
• Urine tests: a urinalysis looks for blood, protein, and signs of infection. A urine culture identifies the bacteria responsible when infection is suspected. A urine protein-to-creatinine ratio measures how much protein is leaking.
• Blood pressure measurement: repeated readings are an important part of both diagnosis and long-term follow-up, since high blood pressure is a common consequence of scarring.
• CT or MRI: these are used less often for scarring itself but may be requested to look for stones, blockage, or other structural causes.

A kidney biopsy, in which a small sample of kidney tissue is removed with a needle and examined under a microscope, is not usually needed to diagnose scarring from infection or reflux. It may be considered in adults when a different underlying kidney disease is suspected.

Treatment options for renal scarring

There is currently no treatment that can reverse an established renal scar or turn scar tissue back into working kidney. Renal scarring treatment therefore focuses on three aims: treating the cause, preventing new scars from forming, and protecting the remaining healthy kidney tissue from further harm. The plan depends on age, the cause, the extent of scarring, and the level of kidney function.

Observation and monitoring

For a small scar in one kidney with normal blood pressure and normal urine tests, doctors often recommend regular monitoring rather than active treatment. This typically includes blood pressure checks, periodic urine tests for protein, and blood tests of kidney function. The frequency of follow-up is decided individually and may become less frequent over time if results remain stable.

Medication

• Antibiotics are used to treat active urinary tract or kidney infections promptly, which is the main way to limit new scarring. In selected children with reflux, a low daily dose of preventive antibiotic (antibiotic prophylaxis) may be prescribed for a period of time. Whether prophylaxis is appropriate is a decision made case by case, weighing benefits against the risks of side effects and antibiotic resistance.
• Blood pressure medicines, particularly angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs), are commonly used when blood pressure is high or when protein is present in the urine. These drugs lower pressure inside the kidney filters and may help slow the loss of function.
• Treatment of underlying conditions such as diabetes or glomerulonephritis follows the standard approach for those diseases.

Procedures and surgery

When vesicoureteral reflux is contributing to repeated infections, a urologist may discuss correcting it. Options include an endoscopic injection, in which a bulking substance is placed at the junction of the ureter and bladder through a thin telescope to reduce backflow, or open or minimally invasive ureteral reimplantation surgery, which repositions the ureter so it enters the bladder at a better angle. Many cases of mild reflux improve on their own as a child grows, so surgery is generally reserved for higher-grade reflux or for children who continue to have infections despite other measures. Obstruction from stones or narrowing is treated by removing the blockage. In rare situations where a kidney is severely scarred, barely functioning, and causing problems such as recurrent infection or uncontrolled blood pressure, removal of that kidney (nephrectomy) may be considered.

Supportive measures

Good bladder and bowel habits are an important part of care, especially for children: regular complete emptying of the bladder, adequate fluid intake, and treatment of constipation all reduce the risk of infection. In adults, controlling blood pressure and blood sugar, avoiding smoking, and using pain relievers of the nonsteroidal anti-inflammatory type only as advised help protect remaining kidney tissue. If kidney function has declined substantially, a nephrologist may recommend dietary adjustments to salt, protein, or potassium. If kidney failure eventually develops, which is uncommon, dialysis or kidney transplantation are the established treatments.

Living with renal scarring and outlook

The outlook for most people with renal scarring is reassuring, although it varies with the extent of scarring and the underlying cause. A single small scar in one kidney, with a normal opposite kidney, usually has little or no effect on overall kidney function, and many people live entirely normal lives without ever noticing it. The kidneys have a considerable reserve, and healthy tissue can compensate for lost areas.

The main long-term concerns are high blood pressure, protein in the urine, and, in a minority of people with extensive scarring in both kidneys, a gradual decline in kidney function that may progress to chronic kidney disease. Because these problems can develop years or even decades after the scar formed, and because they are usually silent at first, ongoing follow-up is generally advised even when a person feels well. How often this is needed is individual; some people are checked annually, others less frequently.

For women with significant renal scarring, pregnancy may carry a higher chance of urinary infection and high blood pressure, so doctors often recommend closer monitoring during pregnancy. Children with renal scarring can usually take part in normal activities and sports. Families are often advised to seek prompt medical assessment for any fever without an obvious cause, since early treatment of infection is the most effective way to prevent further damage.

It is important to remember that a scar seen on a scan is a record of past damage, not necessarily a sign of ongoing disease. With prompt treatment of infections, good blood pressure control, and regular review, many people with renal scarring maintain stable kidney function over the long term, though no outcome can be guaranteed for any individual.

Frequently asked questions

Can renal scarring be reversed?

Established scar tissue in the kidney is permanent and cannot currently be reversed by medication or surgery. However, the appearance of a kidney on a scan taken soon after an infection can improve as temporary inflammation settles, which is why doctors often wait several months before confirming a scar. Treatment aims to prevent new scars and to protect the healthy tissue that remains.

What are the first renal scarring symptoms to look out for?

In most cases there are no early symptoms at all, and the scar is found on imaging after a kidney infection or during investigation of reflux. The earliest measurable signs are often high blood pressure or protein in the urine, which are detected on routine tests rather than felt by the person. Repeated urinary infections or flank pain may point to an underlying problem that could cause scarring.

What are the most common renal scarring causes in children?

In children, the most common cause is a kidney infection, particularly when it occurs in a young child who also has vesicoureteral reflux. Delayed treatment of a febrile urinary tract infection and repeated infections increase the likelihood of a scar forming. Some children also have areas of abnormally developed kidney tissue from birth that look similar to scars on imaging.

How is renal scarring diagnosis usually confirmed?

The most sensitive test is a DMSA renal scan, a nuclear medicine study in which scarred areas show up as regions that do not take up the tracer. Ultrasound is often used first and may show a small or irregular kidney. Blood tests, urine tests, and blood pressure measurement help assess how much the scarring has affected overall kidney function, and a VCUG may be done to check for reflux.

What does renal scarring treatment usually involve?

Treatment depends on the cause and extent. Many people need only regular monitoring of blood pressure, urine, and kidney function. Others may need antibiotics for infections, sometimes as a preventive daily dose, blood pressure medicines that also protect the kidneys, or a procedure to correct reflux or relieve a blockage. Surgery to remove a kidney is rarely needed.

Does renal scarring always lead to kidney failure?

No. Most people with limited scarring, especially when it affects only one kidney, never develop kidney failure. The risk is higher when scarring is extensive and involves both kidneys, or when there is an ongoing disease such as uncontrolled diabetes or high blood pressure. Regular follow-up allows any decline in function to be identified early so that protective treatment can be adjusted.

Can renal scarring be prevented?

Not every case can be prevented, but the risk can be reduced. Prompt diagnosis and treatment of urinary tract and kidney infections, particularly in infants and young children with fever, is the most important step. Managing reflux when it is significant, treating constipation and bladder dysfunction, and controlling blood pressure and diabetes in adults also help protect the kidneys.

When to see a doctor

If you or your child have been told there is renal scarring, follow the monitoring schedule recommended by your care team, which may be arranged through a specialist service such as the Nephrology Department. Seek prompt medical attention if any of the following warning signs occur, because they may indicate an active kidney infection, a blockage, or a significant change in kidney function:

• Fever with pain in the side or back, chills, or shaking, especially in a child with known reflux
• Fever in an infant or young child without an obvious cause such as a cold
• Burning, urgency, or pain when passing urine that does not settle within a day, or that returns repeatedly
• Visible blood in the urine or urine that is persistently cloudy or foul-smelling
• Passing very little urine or being unable to pass urine at all
• Sudden swelling of the face, legs, or ankles, or rapid unexplained weight gain
• Severe headache, blurred vision, or a very high blood pressure reading
• Persistent vomiting, extreme tiredness, confusion, or shortness of breath, which can be signs of markedly reduced kidney function

Severe pain, high fever with vomiting, inability to pass urine, or confusion should be treated as urgent and assessed the same day, through emergency services if necessary. Between scheduled visits, it is also reasonable to ask for an earlier review if blood pressure readings taken at home are consistently higher than usual, or if a new symptom develops that concerns you.