| Where It's Done | Who Does It | How Long It Takes | Discomfort/Pain |
| Hospital radiology suite or office of radiologist. | Radiology technician and physician. | About 4-5 hours. | Minor discomfort of injection and line insertion. Lying still for substantial period may cause numbness. Possible flush, burning sensation, or slight nausea during isotope injection. |
| Results Ready When | Special Equipment | Risks/Complications | Average Cost |
| A few minutes to a few days. | An IV set, the radioisotope, a gamma scintillation camera, and an oscilloscope. | In rare cases, there may be renal system impairment and decreased urine output, but these are usually reversible. | $$$ |
Renal scintigram or captopril renal scan.
PurposeTo evaluate blood flow to the kidneys to help detect any narrowing or blockage of the renal artery.
How it worksWhen blood flow to the kidneys is reduced, the kidneys attempt to improve their blood supply by producing angiotensin, which raises blood pressure and helps maintain their filtration function. In this test, an initial scan is followed by administration of the drug captopril, which suppresses angiotensin production. If a second scan shows a decrease in kidney function, it suggests that angiotensin had been at work as a result of a blockage. No change in function after administering captopril suggests that the renal arteries are not constricted and therefore that the kidneys are not dependent on angiotensin.
Preparation- Your doctor may have you discontinue certain medications in the captopril family for several days prior to the test to improve the accuracy of the test.
- You disrobe and don a hospital gown.
- You will receive an injection of a very small quantity of a short-acting radioactive compound (less than the amount of radiation in two chest X-rays) into a vein, usually in your arm.
- You will lie still while a gamma scintillation camera or scanner detects the rays emitted by the radioactive dye. These rays are converted into a video image, and photographs or videotape of that image are taken over about a 20-minute period.
- Three hours later, you will be given a captopril tablet. After another hour, the process will be repeated, providing the same images as before to show any differences caused by the captopril.
- You will return immediately to normal activities.
- The radioisotope is excreted within about 24 hours. During that time, you should flush the toilet immediately after you urinate to limit your exposure.
If you move during the scan, the images may be inaccurate.
InterpretationIf there is a decrease in kidney filtration (as measured by changes in dye uptake by the kidney) on the scan after the captopril is given compared to the initial scan, there may be a renal artery blockage. If no decrease is present after the captopril is given, filtration is not under the influence of angiotensin, and it is likely that no renal artery blockage exists.
AdvantagesThis is a relatively noninvasive way of screening for renal artery blockage.
Disadvantages- It's simply a screening procedure.
- It does not provide a specific image of the blood vessel.
- Any captopril family drug must be discontinued several days before the test.
- A positive test indicates a 90% chance that you have a blockage. Your physician will probably recommend renal arteriography for an actual view of the blockage.
- A negative test indicates a 90% chance that a renal artery blockage is not the cause of hypertension. In this case, you would be treated for primary hypertension with appropriate drug therapy.
