1. Differential diagnosis of obstructive vs. non-obstructive collecting system (with Frusemide provocation and measurement of transit times).

  2. Evaluation and follow up of renal obstruction

  3. Screening for renovascular disease (with ACE inhibitor). Limited role.


  • Mag-3 is the most widely used imaging agent. It is excreted by both glomerular filtration and tubular secretion and can be used to evaluate renal perfusion and renal obstruction. Differentiation of obstruction vs. non-obstructive hydronephrosis can be made by initiating a brisk diuresis with Frusemide. In an obstructed hydronephrosis washout of activity does not occur, while washout of activity occurs if obstruction is not present. Similarly, in a non-obstructed system cortical transit times should be essentially normal. The renogram before and after ACEI challenge may detect functionally significant renal artery stenosis.

Preparation and Procedure:

  • The patient should be off diuretics for at least 24 hours if possible, and should be well hydrated.

  • The renogram takes about 40 minutes. The entire procedure takes one hour. However, if ACEI challenge is required then up to 2 hours may be needed for the study. Please indicate on the request form whether the patient is on ACEI or not.


  • The study is a well established test. The agents used for the study are non-toxic to the patient and can be used in patients with renal failure and in patients allergic to IVU contrast agent. Although some anatomic information is obtained from a renogram, the test is most valuable in assessing renal physiology.


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Page last reviewed: 05 September 2013