Kidney Ultrasound

Kidney Ultrasound: Information and Get a Scan

A kidney ultrasound is a routine medical scanning procedure that produces detailed images of the kidneys and the surrounding structures in real time, without the need for painful or invasive surgical procedures. Doctors use this type of kidney scan to diagnose (and rule out) a range of kidney conditions. 

In this article, we’re going to discuss what a kidney ultrasound is, why your doctor may suggest you need one and how it works. 

Key Takeaways:

• The kidneys are two, bean-shaped organs that form part of the urinary tract 

• The kidneys are situated in the back of the abdomen and are responsible for maintaining water and electrolyte balance, filtering waste products from the blood and creating urine 

• An ultrasound is a quick, routine, painless scan that uses high-frequency sound waves transmitted through an ultrasound probe called a transducer to create an image of the inside of the body

• A kidney ultrasound is used to help doctors discover what might be causing symptoms such as lower back or side pain, frequent urinary tract infections, blood in the urine or swelling of the face, lower legs and feet

• Doctors use the results from kidney scans to diagnose or rule out several conditions affecting the kidneys, and sometimes the bladder, such as cysts, tumours, inflammation and blockages.

What is a Kidney Ultrasound?

The kidneys are a pair of bean-shaped organs, each about the size of an adult clenched fist. They’re situated inside the abdomen, at the back, close to the lower back, one on the left-hand side of the spine, the other on the right-hand side. 

Their primary functions are to filter waste products from the blood and to maintain the correct fluid (mainly water) and electrolyte balance. (Sodium and potassium are examples of electrolytes; minerals that are essential for regulating various bodily functions such as blood pressure, muscle function and nerve signalling.) 

The kidneys form part of the urinary tract. The urinary tract is made up of:

• Two kidneys (in most people. Some people only have one kidney if they were born without one, donated one, or had it removed for medical reasons). They filter the blood, collect waste products and produce urine

• Two tubes called the ureters, one from each kidney, that transport urine to the bladder

• The bladder, a muscular, sac-like organ that collects urine and stores it until we’re ready to urinate (pee)

• The urethra, a tube that transports urine from the bladder to the outside of the body when we urinate 

A kidney ultrasound scan (also called a renal ultrasound) is a routine, painless scan that creates an image of the size and shape of each kidney, as well as the bladder. Renal ultrasounds give doctors a good idea of the health, structure and function of the kidneys and bladder, how they work together and if there are any blockages, tumours, inflammation or other abnormalities

Ultrasound scans of the kidneys and bladder are carried out as an outpatient procedure and require little preparation. You’ll just need to drink plenty of water 30 minutes before your appointment and ensure you don’t empty your bladder beforehand. Kidney ultrasounds produce the most useful images when taken with a full bladder. 

A kidney ultrasound is carried out by a healthcare provider called a sonographer. During your kidney scan, your sonographer will place a conductive gel on your skin that will feel cold and wet. This helps the ultrasound machine create detailed images. 

They will then move a small ultrasound probe called a transducer over the skin of your lower back to create an image of both kidneys. You may also be asked to turn over so that they can do the same on your lower abdomen and pelvic area to obtain clear images of your bladder. 

Why You Might Need a Kidney Ultrasound

There are various symptoms that might indicate that you need an ultrasound of the kidneys and bladder. If you’re regularly experiencing any of the following symptoms, speak to your doctor or healthcare provider about having a renal ultrasound:

• Pain in your lower back or down your side

• Problems urinating or a weak urine stream (such as a dribble) 

• Frequent urination

• Painful urination 

• Blood in your urine 

• Foamy or darker than usual urine 

• Frequent urinary tract infections (UTIs) 

• Swelling in your lower legs, ankles or feet*

• Facial swelling*

*Swelling is caused by fluid buildup and can indicate that your kidneys aren’t maintaining fluid balance correctly.  

Your doctor may also refer you for a kidney ultrasound if they want to take a biopsy (a sample of tissue that’s examined for unusual cells such as cancer cells). An ultrasound is used in this case to guide the biopsy needles to the right place. Kidney ultrasounds are also used to guide doctors if they’re draining kidney cysts or to check on the health of your kidneys following a kidney transplant. 

What a Kidney Ultrasound Can Diagnose

A kidney ultrasound can be used in the diagnosis of the following conditions: 

• Kidney Stones - mineral deposits that form crystals in the urine and collect in the kidneys

• Hydronephrosis - swelling of one or both of the kidneys due to a buildup of urine, potentially caused by kidney stones, pregnancy, an enlarged prostate or tumours

• Kidney Cysts - fluid-filled sacs that can develop in the kidneys and are usually benign (non-cancerous)

• Polycystic Kidney Disease - a genetic condition that causes multiple cysts to form on the kidneys 

• Kidney Tumours - abnormal growths in the kidneys that can be benign (non-cancerous) or malignant (cancerous) 

• Urinary Tract Obstruction - a blockage in the kidneys or the tubes that restricts the flow of urine, caused by kidney stones, inflammation, infections or tumours 

• Chronic Kidney Disease (CKD) - often associated with high blood pressure or diabetes, CKD reduces kidney function 

• Acute Kidney Injury - a sudden and complete or partial loss of kidney function and often a complication of another serious illness (not a physical injury to the kidneys)

• Kidney Infections - caused by bacteria travelling up the kidneys' ureters, an infection can lead to painful or bloody urination 

• Congenital Kidney Abnormalities - structural and functional abnormalities that a person is born with 

Types of Kidney Ultrasounds

Although the technology remains the same, high-frequency sound waves are used to create an image of the kidneys; different types of ultrasounds are used to scan the kidneys and bladder. Which one you have will depend on your symptoms and your medical history:

Standard Renal Ultrasound

A standard renal ultrasound is the most common type of kidney ultrasound scan. A transducer ultrasound probe is moved over the skin of the lower back while you're lying on your front to create an image of the kidneys and the surrounding structures in real time. 

Renal Doppler Ultrasound

A Doppler ultrasound works in the same way as a standard ultrasound, but uses additional equipment to create an image of the blood vessels and blood flow to and from each kidney. 

Unlike a standard ultrasound that doesn’t make an audible sound, a Doppler ultrasound creates a whoosh-like sound, but the sound waves still cannot be felt as they enter the body. Doctors use Doppler ultrasounds to diagnose or rule out conditions that can cause narrowing or blockages in the renal blood vessels. 

Duplex Renal Ultrasound

A duplex renal ultrasound combines a standard and a Doppler ultrasound to asses the overall health of each kidney, and its blood supply. 

Contrast-Enhanced Renal Ultrasound (CEUS)

A contrast-enhanced renal ultrasound, or CEUS, is a specialist type of ultrasound of the kidneys that uses a gas containing microbubbles as a contrast agent (rather than a dye) to create a clear image of the internal structures of the kidneys. 

The microbubbles are injected into a vein, normally in the arm, before a renal ultrasound. They’re smaller than blood cells and cannot be felt as they move around the body in the bloodstream. As the sound waves from the ultrasound encounter the microbubbles in the kidneys, they reflect and create very light areas on an ultrasound image. A radiologist can then use the images to specifically assess restrictions to blood flow through the kidney tissue. 

Intraoperative Renal Ultrasound

Intraoperative renal ultrasound techniques help guide surgeons to the specific area of the kidney they need when performing surgery or a biopsy. 

How an Ultrasound of the Kidney Works

Ultrasound machines bounce high-frequency sound waves into the body through the skin via a probe called a transducer. A special conductor gel is placed liberally onto the skin, and the transducer is moved slowly, with a fair amount of pressure, over the skin where the gel has been applied. This gel helps the transducer glide over the skin without pulling and also acts as a conductor for the sound waves to enter the skin and the body uninterrupted. 

The sound waves used are too high-pitched to hear, and you won’t feel them entering your body. When the sound waves encounter a structure, such as an organ, soft tissues or bones, they bounce off in the same way as an echo, back to the transducer. 

Each structure the sound waves encounter reflects them in different ways. For example, dense bone reflects them quickly, and soft tissue and gases reflect them more slowly. 

Computers attached to the ultrasound machine pick up these differences and turn them into black-and-white images, which a doctor, called a radiologist, then views to make a diagnosis or rule out certain kidney conditions. 

Equipment Used

An ultrasound machine sits on top of a medical trolley, next to a bed, with a transducer probe attached. A transducer is a small, handheld device. The gel used is a clear gel that feels cold and wet when applied. It’s easily removed afterwards, and as it's a water-based gel, it shouldn't stain your clothing.

Benefits

Ultrasound scans are quick, routine, painless and effective. Unlike x-rays and CT scans, they don’t require the use of ionising radiation and therefore don’t carry the (albeit small) risks associated with radiation exposure that these scans do. 

Risks & Side Effects

There are no known risks or side effects associated with ultrasound scans. The only downside is that you may experience some discomfort when the transducer probe is pressed onto your skin and your full bladder. 

How to Prepare for a Kidney Ultrasound

An ultrasound of the kidneys and bladder requires little preparation, but you’ll need to drink 500ml (half a litre) of water (or other clear fluids) 30 minutes before your appointment. You shouldn’t empty your bladder before your scan, as a kidney ultrasound creates the best and most informative images when you have a full bladder. 

It’s also a good idea to wear loose-fitting clothing that can be easily removed if necessary (to change into a gown). You can eat and take medications as normal before your appointment unless otherwise advised by your doctor. 

The Procedure Explained: What to Expect

Different clinics and sonographers vary, but generally, your kidney ultrasound will take place in the following steps:

1. Change into a Gown if Required - You’ll need to pull your lower clothing down to expose your lower back and abdomen. If you can’t, you’ll be given a medical gown to wear. Your sonographer will also cover the area with a blanket or tissue. 

2. Lie Down on the Exam Table - A kidney ultrasound is taken from the back, so you’ll be asked to lie face down on the medical bed. Your sonographer will make sure you’re comfortable before they begin scanning. 

3. Gel Applied to the Abdomen or Back - The conductor gel will be applied to the skin. 

4. Transducer Moved Over the Area - Your sonographer will then move the transducer slowly over the area, pausing every so often to take images. 

5. May Be Asked to Hold Breath or Change Position - At certain times, they may ask you to hold your breath for a few seconds at a time to ensure you’re as still as possible for the clearest images. If you’re having a bladder ultrasound too, you’ll be asked to turn over, and the process will be repeated with the transducer moved over the skin of your lower abdomen and pelvic area. You may also be scanned whilst lying on either side. 

6. May Be Asked to Empty Your Bladder - You may also be asked to go to the toilet, and the scan repeated on your abdomen with an empty bladder. 

7. Gel Wiped Off After Scan - Your sonographer will then wipe the conductor gel from your skin, and you’ll be able to get dressed. 

What Happens After a Kidney Ultrasound?

After an ultrasound of the kidneys, you’ll be able to go to the toilet to empty your bladder if you weren’t asked to do so during your scan. You’ll be able to return home and to your normal duties (if your symptoms allow) on the same day. 

Getting the Results

Once your radiologist has received your ultrasound images, they’ll assess them for abnormalities and signs of disease. They’ll then get in touch to discuss your results and any treatment options with you. 

Get a Kidney Ultrasound

Having symptoms that indicate a possible medical problem with your kidneys or urinary tract is a worrying and upsetting time. NHS waiting lists can mean that you’ll wait several weeks or even months to get an appointment to discover what might be causing your symptoms. 

Book a private ultrasound with us for faster answers. It couldn’t be simpler - choose a clinic near you and book in for an abdominal ultrasound (that will cover your kidneys and bladder). The sooner you do, the sooner you can begin treatment and get back on track. 

FAQs

Can You See Cancer on a Kidney With Ultrasound?

Yes, kidney tumours can be detected during a kidney ultrasound. 

What is a Dark Spot on a Kidney Ultrasound?

A dark spot on a kidney ultrasound usually suggests a fluid-filled cyst or a collection of infection-related pus. Kidney cysts are usually benign (non-cancerous), and infections can be treated. 

Can Ultrasound Detect Kidney Failure?

Yes, an ultrasound can detect signs of kidney failure, and is usually used as a series of tests and investigations to assess kidney health and ultimately diagnose kidney failure if present. 

Why Would a Doctor Order a Kidney Ultrasound?

There are various reasons why your doctor may recommend a kidney ultrasound. These include having symptoms such as recurrent urinary tract infections, lower back pain and blood in the urine. They may also recommend an ultrasound to check on the health of a transplanted kidney. 

How Long Does a Kidney Ultrasound Take?

A kidney ultrasound takes around 20 to 30 minutes, but you should allow an hour for your appointment. 

How Accurate Is Ultrasound for Kidney Stones?

Ultrasounds are fairly accurate in picking up kidney stones. The larger the stone, the more likely it is to be detected. If a kidney ultrasound doesn’t detect kidney stones but you still have symptoms, your doctor will arrange some further tests. 

What Do Kidney Stones Look Like on Ultrasound?

Kidney stones are often more dense than the kidney tissue surrounding them, and therefore appear as bright white spots on an ultrasound against a darker background. 

References

Kidney and bladder ultrasound scan - Overview. (n.d.-b). Guy’s and St Thomas’ NHS Foundation Trust. https://www.guysandstthomas.nhs.uk/health-information/kidney-and-bladder-ultrasound-scan

Professional, C. C. M. (2025, May 6). Kidney ultrasound. Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/15764-kidney-ultrasound

Kidney ultrasound. (2021, August 8). Johns Hopkins Medicine. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/kidney-ultrasound

Professional, C. C. M. (2025a, April 29). Kidney. Cleveland Clinic. https://my.clevelandclinic.org/health/body/21824-kidney