Definition and Overview

Also known as renal sonography, a kidney ultrasound is a noninvasive imaging procedure that locates and assesses the condition of the kidneys and related structures such as the bladder and ureters. It is used as a diagnostic test to detect cysts, tumours, fluid collection, kidney stones, abscesses, and infection within or around the kidney. It can also be performed to assist in placing needles when taking tissue samples for biopsy, in placing drainage tube, and in draining abscess or fluid from a cyst. Lastly, it can also be performed to assess the blood flow to the kidney through the veins and renal arteries.

Unless there is a congenital defect, a person has two kidneys, one on each side of the back of the abdomen (flank). A size of a person’s fist, each kidney plays a huge role in blood filtration.

As the blood circulates all throughout the body, it delivers nutrients and oxygen to different cells. In turn, the cells release by-products and wastes, which are converted into urine that is excreted by the body. During a cycle, the blood passes through the kidneys, which have nephrons, the blood’s central filtration system. Aside from filtering the blood for toxins and by-products, the kidneys also control the amount of sodium and water in the body, two important components of electrolyte balance.

Sometimes, though, the kidneys malfunction and lose the ability to perform their functions; for example, it may fail to regulate the amount of sodium, which can lead to the blood pressure going up. Unless the condition is corrected, more wastes will build up in the blood, exposing the body to a toxic environment.

Since there are two kidneys and the changes can be very subtle, a person can lose up to 90% of the organ’s functions before experiencing the symptoms of a problem such as pain, changes in urination, blood in the urine, lethargy, and abnormal blood pressure. When these symptoms are present, medical professionals typically recommend a kidney ultrasound.

Who Needs It and Expected Results

A kidney ultrasound may be recommended for people with:

  • Flank pain – While many things can cause pain in the flank (around the lower back area), it is also possible that damaged kidneys or the presence of kidney stones causes it. An ultrasound can accurately locate the kidneys, and assess its overall condition.

  • Changes in urine – One of the telltale signs of a kidney problem is a change in urine. A kidney ultrasound may be recommended if the patient is passing too little urine even if the bladder feels full or if the patient urinates little amounts more frequently. This procedure is also performed when the urine contains blood.

  • High creatinine– Creatinine, which comes from creatine, a molecule used by muscles to produce energy, can be measured by a blood test. If creatinine is past the normal range, it may indicate a problem with the kidneys.

  • Kidney disease - Tumours and cysts can develop in the kidneys resulting in acute or chronic conditions. Some people also acquire hereditary kidney disorders such as polycystic kidney disease. The presence of these conditions warrants a kidney ultrasound.

  • Transplanted kidneysKidney transplant is one of the most common surgeries carried out around the world. New kidneys should be constantly monitored since they are vulnerable to rejection or disease.

Since the procedure is non-invasive, it is generally safe and not painful. Depending on the results of the exam, the diagnosing doctor may request additional tests to confirm a diagnosis or formulate an individualized treatment plan.

How Does It Work?

Unlike other types of ultrasound, a kidney ultrasound does not require any special preparation. The patient does not have to fast or submit urine samples. The procedure is usually carried out in a hospital. The patient will be instructed to remove all accessories before changing to a gown and lying on a flat surface or examination table. The patient may be instructed to lie on the back or turn to the side to easily locate the kidneys.

A cool gel is then applied to the site before a transducer (which appears like a wand) is moved to the area where the kidneys are, delivering sound waves. The waves are then bounced off by the organs and structures such as the muscles and tissues until an image of the kidneys can be seen in real time on a monitor.

The entire test takes at least 20 minutes. The obtained images may be printed, stored digitally, and sent to the doctor, who is going to interpret the results.

Possible Complications and Risks

Since the body is not exposed to radiation and the procedure itself is non-invasive, the risks of complications are extremely low. If there are, they are usually minor. For instance, lying on the examination table for some time may cause anxiety and discomfort while some patients may also develop irritation or even allergic reaction to the gel used.

Certain factors such as the presence of gas in the intestine and obesity may provide an inconclusive or inaccurate result.


  • Lee YZ, McGregor JA, Chong WK. Ultrasound-guided kidney biopsies. Ultrasound Clin. 2009;4:45–55.
  • Salama AD, Cook HT. The renal biopsy. In: Taal MW, Chertow GM, Marsden Pa, et al., eds. Brenner and Rector’s The Kidney. 9th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 28.
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