Renal function analysis: A study in contrast agents

Renal function analysis: A study in contrast agents

Veterinary radiologist Dr. Anthony Pease explains why contrast agents are a quick, easy way to examine the urinary tract.
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Jul 21, 2016

A ventrodorsal radiograph of a 9-month-old puppy dribbling urine. Note the slightly larger right ureter compared to the left (arrow) and the caudal insertion of the ureter into the urethra indicating an ectopic ureter and the cause for the clinical signs. (Radiograph courtesy of Dr. Pease.)

 

Challenge: You need a speedy way to examine a patient’s urinary system that requires less skill and training than ultrasound.

Solution: Contrast agents!

Why: Because contrast agents are excreted by the kidneys, they provide a way to functionally see whether or not the kidneys are working. For example, if the kidneys are experiencing anuric renal failure, the contrast medium will not be excreted through the ureters and will accumulate in the kidneys.

Contrast agents can help diagnose conditions such as ruptured ureters, uteroliths and ectopic ureters, as well. Just give the patient intravenous (IV) contrast medium, take some radiographs at five and 10 minutes, and you’ll be able to see the ureters and whether they go into the urinary bladder or go out into the urethra if the ureters are ectopic, and then you’ll have your diagnosis (see radiograph above).

Take note: It’s easy to become distracted by the different contrast agent options—iohexol (Omnipaque—GE Healthcare), iothalamate meglumine (Conray—Liebel-Flarsheim), diatrizoate meglumine (Hypaque—Amarsham Health). But as long as the patient is normotensive and you don’t have any hydration issues (or the patient is receiving IV fluids), any of these contrast agents should work well and safely.

While using contrast medium will provide some nice functional information, it’s a bit all-or-nothing. It either pinpoints the problem, or it doesn’t. For example, it can’t help you figure out glomerular filtration rates, or things of that nature, but it can help you determine if a dog that’s been hit by a car has a ruptured urinary bladder, ureter or urethra.

 

Anthony Pease, DVM, MS, DACVR, is an associate professor in the Department of Small Animal Clinical Sciences at Michigan State University's College of Veterinary Medicine.

Fun Fact: Pease plays ice hockey as a goalie and recently played in an exhibition game with the Carolina Hurricanes' 2006 Stanley Cup Champion team.