Small or scarred kidney seen by chance on a scan
An ultrasound or CT done for the belly, the back or something else often shows the kidneys too, so the report may say a kidney is small, thin, scarred or brighter than usual. A scan shows what the kidneys look like; blood and urine tests show how well they work. (NHS)(KDIGO 2024) This page covers what the words mean, how kidneys change with age, and which checks come next, not treatment.
What the report means
Imaging lets doctors look at kidney shape, size and symmetry, and signs of a blockage, cysts or reflux. (KDIGO 2024) Guidelines count a structural change seen on imaging as one marker of kidney damage. (KDIGO 2024)(NICE NG203)
| Report wording | What it describes |
|---|---|
| Small kidney or reduced kidney size | Shorter or smaller than usual; one study used below the 10th percentile for length (Wang 2025) |
| Cortical thinning | The outer working layer of the kidney is thinner than usual (KDIGO 2024)(Mlynarska 2022) |
| Scar or scarring | A dent or thin patch in the kidney outline; reviews link scarring to past damage, such as small blocked blood vessels (Mlynarska 2022) |
| Increased echogenicity (echogenic kidneys) | Kidney tissue looks brighter on ultrasound, often a sign of scarring (Wang 2025) |
| Asymmetric kidneys | One kidney is clearly smaller than the other (KDIGO 2024) |
| Atrophy or atrophic kidney | A kidney that has shrunk over time (Wang 2014)(Wang 2025) |
How kidneys change with age
- Some shrinking is expected. A review reports that kidney mass falls by about 10% to 30% from the 40s or 50s to the 70s or 80s, and total kidney volume drops by about 16 cm3 per decade, mostly after age 60. (Mlynarska 2022)
- The cortex thins. In CT scans of 1,344 potential kidney donors aged 18 to 75, the outer layer of the kidney got smaller with age, in step with the normal fall in kidney function. (Wang 2014)
- Other common age changes. Focal thinning of the cortex, calcium spots and simple cysts all become more common with age. (Mlynarska 2022) For cysts, see kidney cyst found by chance.
- When it points to kidney disease. Kidneys shrink, mainly in the cortex, in advanced chronic kidney disease. (Wang 2014) In a study of 1,068 ultrasound reports, small kidneys on both sides and bright kidneys on both sides were linked to a chronic kidney disease diagnosis. (Wang 2025)
These are results from groups of people, not a forecast for one person.
What comes next
- Blood and urine tests. NICE says to offer an eGFR blood test and a urine albumin test (ACR) to adults with structural renal tract disease and other risk factors. (NICE NG203) KDIGO also recommends testing people at risk with both tests. (KDIGO 2024) The NHS describes the same two tests. (NHS) See kidney test results for what the numbers mean.
- Old or new? KDIGO says earlier test results, repeat tests, your history and imaging such as reduced kidney size and cortex thickness help show whether a change has lasted at least 3 months. A single abnormal eGFR or ACR does not prove a long-term problem. (KDIGO 2024)
- Earlier scans. Comparing with an older scan helps show whether a kidney has changed. Bring dates of earlier scans if you have them.
Your doctor decides which tests fit your report, your history and your earlier results.
Who it applies to
Adults told that an ultrasound or CT done for another reason shows a small, thin, scarred or bright kidney. If you already know you have kidney disease, see screenings if you have kidney disease.
MedlinePlus, chronic kidney disease: (MedlinePlus)
"Many people don't have any symptoms until their kidney disease is very advanced." Blood and urine tests "are the only way to know if you have kidney disease."
The NHS says to see a GP for lasting symptoms such as swollen ankles, feet or hands, shortness of breath, tiredness, blood in your pee, or peeing more than usual, especially at night. (NHS)
Routine age-based screening
Diabetes and high blood pressure are the most common causes of chronic kidney disease. (MedlinePlus) That is why routine checks for both tie in with kidney tests.
- Blood pressure. See blood pressure screening and screenings if you have high blood pressure.
- Diabetes. See diabetes screening and screenings if you have diabetes.
- Kidney tests. See kidney disease screening for who is tested and how often. (MedlinePlus)
- Other kidney findings. See kidney stone found by chance and small kidney mass found by chance.
- All screenings by age. See screenings by age and gender.
Where they differ:
- Age as a reason to test. NICE says not to use age on its own as a risk factor for kidney testing. (NICE NG203) Studies show kidney size and function fall with age, so a small kidney in an older adult may partly reflect age. (Mlynarska 2022)(Wang 2014)
- Routine screening in the US. USPSTF has an update in progress for chronic kidney disease screening, and its 2012 statement is out of date. (USPSTF) KDIGO and NICE advise testing people with risk factors. (KDIGO 2024)(NICE NG203)
- What counts as a normal eGFR. The NHS says healthy kidneys filter more than 90 ml/min. (NHS) KDIGO defines chronic kidney disease as a GFR below 60, or another marker of damage, for at least 3 months. (KDIGO 2024)
Your doctor decides what your result means for you.
Questions people ask
Is a small or scarred kidney the same as kidney disease?
Not on its own. Guidelines count a structural change seen on imaging as one sign of kidney damage, and chronic kidney disease means signs of damage or a low GFR that last at least 3 months. Blood and urine tests show how well the kidneys work. Your doctor decides. (KDIGO 2024) (NICE NG203)
Do kidneys get smaller with age?
Yes, a little. A review reports that kidney mass falls by about 10% to 30% between middle age and the 70s or 80s, with most of the volume loss after 60. A CT study of 1,344 adults found the outer layer of the kidney (the cortex) gets thinner with age. (Mlynarska 2022) (Wang 2014)
What tests come next?
Guidance says to check kidney function with a blood test for eGFR and a urine test for albumin (ACR). NICE lists structural renal tract disease among the reasons to offer both tests. (NICE NG203) (KDIGO 2024) (NHS)
Does one abnormal test result confirm a long-term problem?
No. KDIGO says not to assume a long-term problem from a single abnormal eGFR or ACR. Earlier results, repeat tests and imaging, including kidney size and cortex thickness, help show whether a change is old. (KDIGO 2024)
What does "echogenic kidneys" mean on an ultrasound report?
It means the kidney tissue looks brighter than usual on ultrasound. In one study of 1,068 ultrasound reports, bright kidneys on both sides and small kidneys on both sides were the findings most linked to a diagnosis of chronic kidney disease. (Wang 2025)
Related
- Swollen kidney (hydronephrosis) seen by chance on a scan
- Bladder wall thickening seen by chance on a scan
- Kidney test results: eGFR and uACR
- Kidney disease screening
- Kidney cyst found by chance: Bosniak follow-up
- Kidney stone found by chance: follow-up
- Small kidney mass found by chance: follow-up scans
- Screenings if you have kidney disease
- After an abnormal screening result
- Screenings by age and gender