A renal Doppler is a non-invasive medical test that uses ultrasound technology display the kidneys and surrounding blood vessels. Doctors and medical care providers use it to detect kidney abnormalities and to assess the organs’ overall health. It is typically only used when problems are suspected, which is to say that it isn’t normally a part of routine checks or exams. The procedure itself is painless, but it can be quite expensive to perform and may carry some associated risks. As a result, it is usually only used when necessary to diagnose or rule out specific problems.
How it Works
Doppler ultrasounds use sound wave technology to look at blood flow in targeted parts of the body, and in the renal context they are focused specifically on one or both kidneys. In most cases the sound waves pass through a hand-held wand, called a transducer. They bounce off of red blood cells as they circulate, then translate the speeds and measurements detected into a visual image, usually on an attached computer screen. Technicians and medical experts can manipulate those images further by honing in on different areas and zones.
Patients sometimes have to prepare for these procedures in advance. Pre-test procedures vary by care provider, but in general people are asked to not consume any food or beverage for at least eight hours prior to the procedure, with the exception of small quantities of water. Carbonated beverages in particular should be avoided, as the carbonation can interfere with the testing procedure and can skew the images.
It’s also common for patients to be given water to drink prior to starting the procedure in order to stimulate the kidneys and trigger more vigorous blood flow. People are usually required to remove clothing and anything else that could interfere with the testing process, like jewelry or other accessories; sometimes undergarments can stay on, but more often people wear surgical gowns. Most of the time patients lie down on an examining table, though reclining in an ultrasound chair is sometimes also possible. The technician will apply a clear gel to the skin over the abdomen to allow the transducer to glide, which in turn can help produce a clearer, smoother image.
Why It’s Used
Renal Doppler procedures are traditionally used to detect conditions such as renal artery stenosis, which is a narrowing and hardening of the arteries flowing to and from the kidneys. Stenosis is a form of atherosclerosis, which results in blood flow restriction; where the kidneys are concerned, this can cause a number of problems. Impaired kidney function can impact everything from digestive health to blood chemistry. Renal artery stenosis is most commonly found in people over 50, but can happen to almost anyone.
If doctors suspect hypertension, sometimes referred to as unilateral stenosis, they may also order a Doppler. Hypertension happens when blood flow to one kidney is restricted due to a narrowing of the artery and is frequently associated with high blood pressure. Bilateral stenosis, or renal failure, results from limited blood flow to both kidneys and is normally related to diminished kidney function. Risk factors such as diabetes and smoking greatly increase an individual's chance of developing these conditions, but sometimes they happen as a result of genetics, illness, or unrelated injury.
Doppler scanning is also an efficient way to detect the presence of kidney stones, which are calcium deposits that lodge in the renal passageways and can cause pain along with a number of different symptoms. These blockages change the way that blood flows to and through the kidneys, and trained technicians can usually notice these changes pretty quickly in the translated image.
Renal Doppler testing is usually considered safe from a medical standpoint, and it is often a good alternative to radiation-based X-rays and more invasive tests like contrast dye scans. As a result it is generally safe for people who have dye allergies, as well as women who are pregnant. The biggest risks come in the form of misdiagnosis, usually as a result of other underlying conditions that can interfere with the test. Obesity, for instance, can skew the results, as can certain blood chemistry imbalances. People who suffer from chronic intestinal gas sometimes also find that Doppler scans are inconclusive or simply wrong, too.