How is renovascular hypertension diagnosed?
It is important to see a doctor regularly to make sure blood pressure numbers are checked and are within the normal range. He or she may recommend blood tests be done.
A healthcare provider can gather clues that vascular disease may be present by taking a thorough history and performing a physical exam. Patients with a history of other vascular disease, such as heart attacks or strokes are at higher risk for having renal artery stenosis. One exam, listening to the neck or belly with a stethoscope may help identify narrowed arteries. When blood flows through a narrowed artery, it sometimes makes a whooshing sound, called a bruit.
Healthcare providers will usually think of renovascular hypertension when the blood pressure suddenly worsens in an older patient, develops in younger patients, worsens in the setting of worsening kidney function, or is very difficult to control despite using three or more medications. Providers may order one of the imaging tests below to look for narrowed kidney arteries. However, finding a narrowed kidney artery alone does not mean that the high blood pressure is due to renovascular hypertension. Many patients have narrowing of kidney arteries without high blood pressure or with high blood pressure that is not caused by the narrowing (essential hypertension). The provider will need to use other clinical clues to help determine if the two are connected.
Imaging tests that can be done to see if the kidneys’ arteries have narrowed include:
- Duplex ultrasound: Images from this test can show blockage in the renal artery or blood moving through nearby arteries at a higher-than-normal speed. Ultrasound is noninvasive, meaning that no medical instruments enter the body and does not expose the patient to radiation. It is a good starting test. However, it does not find all cases of renal artery stenosis, cannot always tell how narrowed the artery is, and may be less accurate if the technician performing the test is not highly skilled.
- Computerized tomographic angiography, or CTA: This procedure uses both x-rays and computer technology to create images. Contrast medium is injected into a vein in the patient’s arm to better see the structure of the arteries. The patient is awake during this test and will lie on a table that slides into a doughnut-shaped device where the x-rays are taken. The test is fairly quick. Claustrophobia is not a major problem with this test. Because x-rays are used, the patient is exposed to some radiation. This procedure may not be an option for those with poor kidney function because of the need to use contrast dye.
- Magnetic resonance angiogram, or MRA: Images from this test show blood flow and organ function without using x-rays. Contrast medium may be injected into a vein in the person’s arm to better see the structure of the arteries. The patient remains awake, although a muscle relaxer may be used, if necessary. The patient lies still on a table that slides into a tunnel-shaped device. This procedure may not be an option for those with very poor kidney function due to the contrast dye, although the dye is safe in patients with kidney function (GFR) >30cc/min. There is no radiation exposure with this study. Claustrophobia can be an issue with MRA’s as the tube is quite narrow.
- Catheter angiogram: A special kind of x-ray in which a catheter, or a thin, flexible tube, is threaded through the large arteries into the renal artery. This often is from a small slit in the groin. The patient is usually awake, although a muscle relaxer may be given to lessen anxiety during the procedure. Contrast medium, or a colored dye, is injected through the catheter, so the renal artery shows up more clearly on the x-ray. The benefits of this study are that it is more accurate than the other tests and if a significant narrowing is seen, it can be dilated with a balloon (angioplasty) or stented (a tube-like cage that keeps the vessels open) at the same time. A catheter angiogram is an invasive procedure so this is usually reserved for patients who have a positive result of one of the other tests and plans are made to dilate the blood vessel.