Why a Renal Ultrasound May Be Recommended
Blood and urine tests can provide important information about how well the kidneys are working, but they cannot show what the kidneys physically look like. When a clinician needs more information about kidney size, structure, or the urinary tract, a renal ultrasound may be recommended.
A renal ultrasound uses sound waves to create images of the kidneys and nearby structures. The test is noninvasive, does not use ionizing radiation, and generally does not require anesthesia. It may be ordered after abnormal kidney laboratory results, urinary symptoms, recurrent infections, unexplained changes in kidney function, or other findings that suggest a structural problem.
Nephrology Associates of Northern Illinois and Indiana (NANI) evaluates patients in Berwyn and North Chicago, Illinois, and Bergen, New Jersey, for a range of kidney concerns. Ultrasound findings can add another piece of information when blood tests, urine testing, symptoms, and medical history do not provide the full picture.
What a Renal Ultrasound Can Show
During the test, ultrasound images allow the healthcare team to look at several physical characteristics of the kidneys.
The kidneys are evaluated for their location, size, shape, and general appearance. Ultrasound may also reveal cysts, swelling of the kidney from backed-up urine, certain stones, masses, or other structural changes.
Kidney size can sometimes provide useful context. For example, chronically damaged kidneys may become smaller over time, although kidney size alone cannot determine the cause or severity of kidney disease.
Ultrasound findings are therefore interpreted alongside kidney function measurements such as creatinine and eGFR rather than being used as a standalone assessment.
Reasons a Kidney Ultrasound May Be Ordered
A clinician may recommend ultrasound for many different reasons. The purpose depends on the patient’s symptoms, laboratory findings, and medical history.
Common reasons include:
- An unexplained decline in kidney function
- Blood in the urine
- Recurrent urinary tract infections
- Flank or back pain that may involve the kidneys
- Suspected urinary obstruction or hydronephrosis
- Evaluation of kidney cysts
- Concerns about kidney size or structure
- Follow-up of a previously identified abnormality
- Evaluation for certain forms of chronic kidney disease
Not every abnormal kidney test requires imaging. In many cases, the decision is based on whether ultrasound is likely to answer a specific clinical question.
Looking for Urinary Blockages
One particularly useful role of renal ultrasound is identifying hydronephrosis. This occurs when urine backs up into the kidney and causes part of the urinary collecting system to become enlarged.
A blockage may develop because of a kidney stone, prostate enlargement, narrowing within the urinary tract, or another obstruction.
When kidney function worsens unexpectedly, determining whether urine flow is blocked can be important because obstruction may require a different approach than kidney damage caused by diabetes, hypertension, or an inflammatory condition.
Ultrasound can show enlargement associated with hydronephrosis, although additional imaging may sometimes be needed to determine exactly what is causing the blockage.
Identifying Kidney Cysts
Kidney cysts are fluid-filled sacs that may be discovered during ultrasound. Simple kidney cysts become more common with age and often cause no symptoms or loss of kidney function.
Ultrasound can help show the size, location, and general characteristics of a cyst. Some simple cysts require no treatment, while other findings may lead to additional imaging or monitoring.
More complex cystic conditions are different from an isolated simple cyst. For example, inherited disorders such as polycystic kidney disease can involve multiple cysts and may affect kidney structure and function over time.
An ultrasound finding should therefore be interpreted within the context of the patient’s family history, laboratory results, symptoms, and overall kidney disease evaluation.
Can Ultrasound Detect Kidney Stones?
Some kidney stones can be seen with ultrasound, particularly when they cause obstruction or changes in the urinary collecting system.
However, ultrasound does not identify every stone as clearly as other imaging methods. Computed tomography, or CT, may provide more detailed information in certain situations.
The choice between ultrasound and CT depends on the clinical question. Ultrasound has the advantage of avoiding radiation, while CT may be more sensitive for identifying certain stones and defining their size and location.
A healthcare professional determines which imaging method is most appropriate based on symptoms and the information needed.
What Happens During the Test?
A renal ultrasound is typically performed in a medical office, imaging center, or hospital. Patients usually lie on an examination table while a trained sonographer performs the study.
A gel is applied to the skin over the abdomen, sides, or back. The sonographer moves a handheld device called a transducer across the skin. The transducer sends sound waves into the body and receives the echoes that return from internal structures.
These signals are converted into images on a monitor.
Patients may be asked to change position so the kidneys can be viewed from different angles. Depending on the type of study, the bladder may also be evaluated.
The test itself is generally painless, although pressure from the transducer may feel uncomfortable over an area that is already tender.
Preparing for a Renal Ultrasound
Preparation requirements vary depending on what structures need to be examined.
Some patients may be instructed to drink water and arrive with a full bladder, particularly if the bladder and urinary tract are being evaluated along with the kidneys. Others may receive different instructions based on the imaging center’s protocol.
Patients should follow the specific directions provided when the test is scheduled rather than assuming that every renal ultrasound requires the same preparation.
Routine medications usually do not need to be stopped unless the healthcare team gives separate instructions.
One advantage of ultrasound is that it typically does not require injected contrast dye. This can make it useful when clinicians want structural imaging without exposing a patient to contrast agents that may require additional consideration in people with reduced kidney function.
What the Results Can and Cannot Tell You
A renal ultrasound can reveal structural abnormalities, but it cannot fully measure how well the kidneys are performing their filtering functions.
A kidney may appear relatively normal on imaging while blood and urine testing reveal chronic kidney disease. Conversely, ultrasound may show cysts or other structural findings even when filtration remains relatively stable.
This is why imaging results are usually reviewed alongside eGFR, urine albumin, blood pressure, medical history, and other clinical information.
Following kidney protection recommendations may still be important even when ultrasound findings are reassuring, particularly for patients with diabetes, hypertension, proteinuria, or other risk factors.
When More Imaging May Be Needed
Ultrasound often provides enough information to answer the initial clinical question, but sometimes another type of imaging is necessary.
CT scans can provide more detailed views of stones, tumors, infections, injuries, and certain urinary tract abnormalities. Magnetic resonance imaging, or MRI, may be useful when detailed soft-tissue or blood-vessel imaging is needed.
The need for additional imaging does not necessarily mean that something serious was found. An ultrasound may simply identify an area that cannot be fully characterized with sound waves alone.
The clinician and radiologist use the ultrasound findings, symptoms, laboratory results, and medical history to determine whether further testing would provide meaningful information.
Putting Imaging Into the Larger Kidney Evaluation
Renal ultrasound is valuable because it answers questions that laboratory testing cannot. It can show whether the kidneys are unusually small or enlarged, whether urine appears to be backing up, and whether cysts or other structural abnormalities are present.
At the same time, ultrasound is only one part of kidney evaluation. Blood tests reveal how well the kidneys are filtering, urine testing can identify protein or blood, and medical history may point toward diabetes, hypertension, inherited disease, medication effects, or another cause.
For patients receiving nephrology care through NANI in Berwyn and North Chicago, Illinois, and Bergen, New Jersey, renal ultrasound may be used when structural information can help clarify abnormal laboratory findings or symptoms. Combining imaging with blood and urine testing gives the care team a more complete view of kidney health.
Sources
Kidney Disease: Improving Global Outcomes CKD Work Group. (2024). KDIGO clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney International.
O’Neill, W. C. (2000). Sonographic evaluation of renal failure. American Journal of Kidney Diseases.
Moghazi, S., Jones, E., Schroepple, J., et al. (2005). Correlation of renal histopathology with sonographic findings. Kidney International.
