Nuclear Medicine Renal Scan

Authors: Dr Chian Chang*
Dr Dee Nandurkar *

What is a renal scan

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.

What are the generally accepted indications for a renal scan?

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:

• renal tubular function and perfusion;
• renovascular hypertension;
• renal artery stenosis;
• ureteric obstruction, trauma or damage;
• renal transplant perfusion and function.

What are the prerequistes for having a renal scan done?

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:

• duplex or dilated collecting systems;
• polycystic kidney disease;
• renal transplant.

What are the absolute contraindications for a renal scan?

• Pregnancy

What are the relative contraindications for a renal scan?

• Coexisting angiotensin-converting enzyme inhibitors if the scan is being carried out for renovascular hypertension.
• If the patient is breast-feeding, please discuss the logistics of the scan with the nuclear medicine department. The radiopharmaceutical is excreted into the breast milk. Expressing breast milk and stopping breast-feeding for 24 hours is the most common advice in this case, but avoiding uneccessary radiation to the child and others would need to be discussed.
• If the patient is breast-feeding, please discuss the logistics of the scan with the nuclear medicine department. The radiopharmaceutical is excreted into the breast milk. Expressing breast milk and stopping breast-feeding for 24 hours is the most common advice in this case, but avoiding uneccessary radiation to the child and others would need to be discussed.
• Obesity: Please contact the nuclear medicine department if the patient is significantly overweight or obese. Most modern gamma cameras have weight limits ranging from 160 to 220 kg.
• Renal impairment: In patients with renal impairment (eGFR <30–45) MAG3 may be more appropriate than DTPA. MAG3 is cleared by tubular excretion, with higher renal uptake giving better renal to background images. Therefore, MAG3 is recommended for neonates, patients with impaired function or suspected obstruction. There are no different preparation requirements or side effects.

What are the adverse effects of a renal scan

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.

Is there any specific post procedural care required following a renal scan?

It is recommended that patients remain well hydrated after the test, as the effects of diuretics, if administered, may persist.

Are there alternative imaging tests, interventions or surgical procedures to a renal scan?

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.

*The author has no conflict of interest with this topic.

Page last modified on 24/8/2018.