Chorionic Villous Sampling
What are the generally accepted indications for chorionic villous sampling? Chorionic villous sampling (CVS) is usually carried out between 11…Read more
A nuclear medicine renal scan is used to assess blood flow, function and drainage of the kidneys. The radio-isotope, 99m-Tc, is bound to either DTPA (diethylene triamine pentaacetic acid) or MAG3 (mercaptoacetyletriglycine) to form the radiopharmaceutical. The radiopharmaceutical is then injected into a vein and enters the kidneys. The radioactive component of the radiopharmaceutical emits gamma rays, which allows us to image the kidneys using a gamma camera. For indications such as renal tract obstruction, often a loop diuretic (frusemide) is administered. For renovascular hypertension, a short-acting angiotensin-converting enzyme inhibitor, such as captopril, is administered.
Nuclear medicine renal scanning is carried out to assess the percentage each kidney contributes to the total renal function. A DTPA or MAG3 scan may also be done to evaluate:
For renovascular hypertension, the patient needs to be well hydrated. Some institutions require patients to also fast 4 hours before the scan to ensure the oral captopril administered is absorbed quickly.
Patients on angiotensin II receptor blocker or angiotensin-converting enzyme inhibitors should cease their medications before the test, as a captopril challenge is involved in the test. Long-acting agents (such as perindopril) and short-acting agents (such as captopril) should be ceased 4–7 days and 3 days before the test, respectively.
Furthermore, it is recommended that long-term diuretics are ceased 1–2 days before the test if clinically safe. Their use may lead to volume depletion and a consequent false negative result. Please discuss this with the nuclear medicine specialist.
Although not always essential, some radioisotope scans may require correlation with a renal ultrasound scan or other anatomical imaging techniques (e.g. CT) in assessing:
There are no known associated risks; however, the patient will be receiving a dose of radiation (See InsideRadiology: Radiation risk of medical imaging for adults and children).
Captopril and diuretics administered may result in hypotension. In general, if patients are well hydrated, this is unlikely. All patients will have an intravenous cannula inserted during the scan and can be adequately fluid resuscitated should this occur.
It is recommended that patients remain well hydrated after the test, as the effects of diuretics, if administered, may persist.
Nuclear medicine scanning is the ideal investigation for renal function assessment. Ultrasound, CT or MRI are better for structural assessment (e.g. renal cortical thickness, parenchymal pathology and obstruction). A renal DMSA scan can be used to assess the ‘amount’ of functional renal tissue compared with non-functioning scars.
Page last modified on 24/8/2018.
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