Renal Scarring: Causes, Symptoms, and Management

Renal scarring is permanent damage to the kidney’s functional tissue, replacing normal structures with fibrous scar tissue that can no longer filter blood or regulate fluid balance. It develops most often after severe or repeated kidney infections, particularly in children, but chronic conditions like uncontrolled high blood pressure and diabetes also drive it in adults. The scarring itself is usually silent until enough tissue is lost to affect kidney function, which makes detection and prevention far more important than treatment after the fact.

How Kidney Infections Lead to Scarring

The most well-studied cause of renal scarring, especially in children, is acute pyelonephritis, a bacterial infection that reaches the kidney rather than staying confined to the bladder. This type of infection can trigger permanent scarring that later raises the risk of high blood pressure, protein in the urine, pregnancy complications like preeclampsia, and progressive kidney insufficiency.¹ The scarring is not caused directly by the bacteria themselves. Animal research using uropathogenic E. coli shows that the degree of fibrosis tracks most closely with the intensity of the body’s inflammatory response at one and four weeks after infection, not with bacterial load alone.² In other words, the immune system’s own overreaction to infection does much of the lasting damage.

Once inflammation recruits large numbers of immune cells into the kidney tissue, those cells release signaling molecules that activate specialized cells called myofibroblasts. These myofibroblasts produce enormous amounts of connective-tissue matrix, essentially laying down scar material faster than the kidney can clear it away.³ The result is an imbalance between new scar production and scar breakdown, and over time this tips irreversibly toward fibrosis.⁴

Vesicoureteral Reflux and Congenital Factors

Vesicoureteral reflux (VUR) is a condition, usually diagnosed in childhood, where urine flows backward from the bladder toward the kidneys. It is one of the strongest known risk factors for renal scarring, not because the backward flow of sterile urine is itself harmful, but because reflux makes it far easier for bacteria to reach the kidney during a urinary tract infection. Specific risk factors for scarring in children with VUR include higher grades of reflux, dysfunctional voiding patterns, repeated episodes of pyelonephritis, and delays in starting antibiotics. Low-pressure sterile reflux, on its own, does not cause reflux nephropathy.⁵

That distinction matters because it shapes how aggressively doctors treat VUR. Some children are born with kidneys that already show abnormal development, sometimes called congenital reflux nephropathy, which can look similar to acquired scarring on imaging but has a different origin. For acquired scarring, the focus is on preventing infections and treating them quickly when they occur.

Hypertension and Diabetes as Slower Drivers

In adults, the two most common roads to renal scarring run through chronically elevated blood pressure and poorly controlled blood sugar. Sustained hypertension injures the small blood vessels in the kidney, causing thickening of vessel walls (a process called hyalinosis), shrinking of glomeruli, and fibrosis of the tissue between tubules.⁶ Nephrosclerosis, the umbrella term for these hypertension- and aging-related kidney changes, is an extremely common finding in older adults and contributes to a gradual loss of functional kidney tissue over decades.⁷

Diabetes drives scarring through a different but overlapping pathway. High glucose levels damage the glomerulus and the surrounding tubulointerstitial region simultaneously, producing a gradual scarring of both compartments that worsens as blood sugar control deteriorates over years.⁸ Because diabetes and hypertension so often coexist, many patients develop overlapping patterns of kidney damage from both conditions at once, which can accelerate the timeline toward chronic kidney disease.

Why Some People Scar and Others Do Not

One of the frustrating realities of renal scarring is that two children can have the same infection, the same grade of reflux, and the same treatment timeline, yet one develops significant scars and the other recovers with a normal-looking kidney. Genetics appears to explain part of this variability. A systematic review and meta-analysis of candidate gene studies found that variants in the angiotensin-converting enzyme gene (specifically the insertion/deletion polymorphism) and the TGF-β1 gene promoter were both associated with a modestly increased risk of scarring after urinary tract infections.⁹

A study focusing on TGF-β1 and VEGF gene variants found that one particular TGF-β1 promoter variant was present in roughly half of children with renal scarring but only about a quarter of non-scarring patients and healthy controls. After accounting for the presence of VUR, this genetic variant remained an independent predictor of scarring, with a roughly sixfold increase in odds.¹⁰ More recent work has also pointed to mitochondrial gene variants as part of the susceptibility profile, suggesting that the cell’s energy machinery plays a role in how well the kidney withstands and recovers from infection.¹¹

None of these genetic markers is used in routine clinical practice yet, but they help explain why scarring is not simply a matter of how bad the infection was or how quickly antibiotics were given.

Symptoms, or the Lack of Them

Renal scarring itself does not cause pain. There is no telltale symptom that alerts you to scar formation the way, say, a rash signals a skin condition. During an acute kidney infection, you may have fever, flank pain, and painful urination, but those symptoms come from the infection, not the scarring that may follow. Once the infection resolves, the scarring that forms is clinically silent until it becomes extensive enough to compromise overall kidney function.

When scarring is severe or affects both kidneys, the downstream effects can eventually include persistently elevated blood pressure, protein appearing in the urine, and a slow decline in kidney filtration capacity. Scarred kidneys tend to activate the body’s blood-pressure-regulating hormone system, leading to salt and water retention and a rise in blood pressure.¹² In a long-term study of children with VUR, the presence of renal scarring roughly tripled the hazard of developing stage 2 or higher chronic kidney disease compared to children without scars.¹³

Detecting Scars With Imaging

The gold standard for finding renal scars in children is a DMSA scan, a nuclear medicine study that uses a radioactive tracer to map which parts of the kidney are taking up the tracer normally and which are not. Scarred areas show up as cold spots, regions of reduced or absent uptake. The problem with DMSA scans is that they involve radiation exposure and are not always convenient, which has led many clinicians to wonder whether a standard ultrasound could substitute.

The short answer is no. Ultrasound has excellent specificity, meaning that when it shows a scar, the scar is almost certainly there. But its sensitivity is poor. One study found that ultrasound detected only about 5% of focal scars identified by DMSA, and even for more widespread scarring, sensitivity was under 50%.¹⁴ A more recent pediatric study reported a similar picture, with ultrasound sensitivity around 36% and specificity near 90%.¹⁵ In another comparison, a DMSA scan found scars in 35% of kidneys that ultrasound had called normal.¹⁶ A normal ultrasound does not rule out renal scarring.

Emerging Biomarkers and Advanced Imaging

Because DMSA scans involve radiation and ultrasound misses too many scars, researchers have been looking for blood or urine tests that could flag at-risk children without imaging. Among the candidates, urinary NGAL (neutrophil gelatinase-associated lipocalin) adjusted for creatinine has shown the most consistent results, with one study reporting sensitivity around 84% and specificity around 81%.¹⁷ Other markers like MMP-9 and TIMP-1, enzymes involved in tissue remodeling, have also shown promise in identifying children at risk after acute pyelonephritis.¹⁸ None of these tests has reached routine clinical use, but urinary NGAL in particular is getting close to the point where it could reduce the number of DMSA scans children need.

For adults with chronic kidney disease, advanced MRI techniques are being explored as a way to assess fibrosis without a biopsy. Diffusion-weighted imaging can measure how freely water molecules move through kidney tissue; in fibrotic kidneys, that movement is restricted. One study found that a measure called the apparent diffusion coefficient correlated strongly with the degree of fibrosis seen under the microscope, and could distinguish between moderate and severe fibrosis with an area under the curve above 0.90.¹⁹ Other functional MRI approaches, including arterial spin labeling and blood-oxygen-level-dependent imaging, are being studied for the same purpose and may eventually allow dynamic monitoring of fibrosis progression without repeated biopsies.²⁰ A separate study confirmed that the difference in apparent diffusion coefficient between kidney cortex and medulla correlated with biopsy-confirmed fibrosis and could predict decline in kidney function over time.²¹

Can Early Antibiotics Prevent Scarring?

The intuitive assumption is that treating a kidney infection faster should reduce the chance of scarring. This turns out to be less straightforward than it sounds. In a rat model, antibiotics started within the first day of infection could prevent scarring, but treatment begun more than 24 hours after infection had no significant impact on eventual scar formation. The critical threshold appeared to be the arrival of a second wave of immune cells; once those cells were established in the infected tissue, antibiotics could not undo the inflammatory damage already set in motion.²²

In children, the clinical data is even more humbling. A large Italian study found that delaying antibiotic treatment from less than one day to five or more days after fever onset did not significantly increase the risk of scarring on DMSA scans done a year later. The scarring rate stayed relatively flat at around 31% regardless of treatment timing.²³ This does not mean antibiotics are unimportant for pyelonephritis, since they clear the infection and prevent sepsis, but they appear to have limited power to prevent the scarring itself once the inflammatory cascade is underway.

Antibiotic Prophylaxis and Reflux Surgery

For children with VUR who are at ongoing risk of repeated kidney infections, doctors often prescribe low-dose daily antibiotics to prevent infections from happening in the first place. A systematic review and meta-analysis found that continuous prophylaxis significantly reduced the odds of recurrent febrile or symptomatic UTIs, but did not reduce the rate of new renal scarring. There was a meaningful trade-off: children on long-term antibiotics were about nine times more likely to develop infections with antibiotic-resistant bacteria.²⁴

A randomized trial in infants with moderate-to-severe VUR echoed this pattern. Prophylaxis roughly halved the rate of first UTI over two years compared to no treatment, but the incidence of new kidney scars and kidney function at two years did not differ between the groups. About two-thirds of untreated children had no UTI at all during the trial period.²⁵ These findings have made the decision to use prophylaxis more nuanced; it is now weighed against the risk of breeding resistant organisms and the recognition that preventing UTIs does not automatically prevent scars.

Surgical correction of VUR, typically through ureteral reimplantation, is highly effective at eliminating reflux, with resolution rates above 90% for grades up through IV. But it is an invasive procedure requiring hospitalization, with a complication rate of roughly 5 to 9%.²⁶ Endoscopic injection, a less invasive alternative, is also used, with variable success rates depending on reflux grade. The decision between watchful waiting, prophylaxis, endoscopic treatment, and surgery is increasingly individualized based on reflux severity, the child’s history of breakthrough infections, and whether scars are already present.

Managing Established Scarring

Once scarring has formed, the kidney tissue is not coming back. Management shifts toward slowing further damage and controlling the consequences. For adults and older children with scarring-related kidney disease, medications that block the renin-angiotensin system, including ACE inhibitors and angiotensin receptor blockers, are a cornerstone. These drugs lower blood pressure within the kidney’s filtration units and reduce protein leakage into the urine. In a small series of patients with hereditary nephritis, ACE inhibitor therapy dramatically reduced urinary protein levels and appeared to stabilize the decline in kidney function.²⁷

Newer agents, particularly SGLT2 inhibitors originally developed for diabetes, have shown benefits in slowing kidney disease progression and reducing heart failure risk when used alongside renin-angiotensin blockers, even in people without diabetes.²⁸ The combination of blood pressure control, protein reduction in urine, and these newer medications represents the current best strategy for preserving whatever kidney function remains after scarring.

Pregnancy and Renal Scarring

Women who had kidney infections or VUR as children sometimes worry about whether renal scarring will complicate a future pregnancy. The evidence is somewhat reassuring but conditional. A study comparing pregnancies in women with and without renal scarring from childhood UTIs found no significant difference in rates of preeclampsia, operative delivery, prematurity, or birth weight, though the authors noted that the women with severe scarring had been under continuous clinical supervision throughout pregnancy.²⁹

A review of published studies clarified an important distinction: VUR without scarring did not increase pregnancy complications at all, whether the reflux had been diagnosed in childhood or adulthood. It was renal scarring itself, rather than the reflux, that was the primary risk factor for pregnancy-related morbidity, and this risk existed regardless of whether reflux was still present at the time of pregnancy.³⁰ The practical takeaway is that women with known renal scars benefit from early referral to a specialist who can monitor kidney function and blood pressure closely through pregnancy, but most will have uncomplicated outcomes with appropriate surveillance.

Quality of Life for Children With VUR and Scarring

The medical discussions around renal scarring tend to focus on kidney function numbers and imaging findings, but the lived experience of children and families dealing with VUR, repeated UTIs, and the prospect of scarring is a separate concern. Children with VUR reported quality of life broadly comparable to healthy peers, but with lower scores on measures of stomach complaints, behavior, and communication, likely reflecting the toll of chronic medical appointments, imaging studies, and ongoing antibiotic use.³¹

When treatment leads to resolution of reflux and regression of scars, quality-of-life scores improve substantially. In one study tracking children before and after endoscopic treatment, those whose scars regressed on follow-up DMSA scans had the highest gains in health-related quality of life, while the small number who showed scar progression had the lowest.³² These findings remind clinicians that the goal is not just protecting kidney function on paper but preserving a child’s normal experience of childhood, something that frequent catheterizations, nuclear scans, and daily medications can easily erode.