VCUG is done while voiding (the V in VCUG) to see if there is any reflux of the urine back up into the ureters. In your case, IVP or CT scan would probably be the first ordered study for pyelonephritis or hematuria.
Usually VCUG is used in kids who keep getting UTIs to see if there's reflux. I'm not sure I've seen a VCUG used in another clinical setting besides looking for reflux or incompetent valves.
I've completed 3rd year, but I've yet to see a good explanation of the reasons/rationale for these tests. I am aware of VCUG usage for posterior urethral valves and other causes of obstruction...was also wondering if it had broader applications?
I guess the question would have been better asked as "What exactly does IVP show you and when is it used?"
The most common cause of UTI/Pyelo in a young male (or old male for that matter) is an anatomic abnormality...so why wouldn't VCUG be the better test? <i.e. it would show vesicoureteral reflux>
It's more geared towards the layperson, but you might find it useful. another option would be looking it up in a urology or radiology textbook.
edits
PS -- I think CT would be the first imaging step if you were to order one. IVP isn't used that much now.
PPS -- if you have access to the book, Urology Secrets, you might like it. It's a question answer based book (one of the questions is: "what is the best radiologic test in acute pyelonephritis" and it goes through the options including plain films, IVP, CT, US, and renal nuclear scan, each of which help to show different things. They end that section by saying contrast CT is often the study of choice if imaging is indicated).
Books are generally better sources of information than anonymous message boards.
An IVP is a functional and anatomic study of the upper urinary tract. It is functional in that you can see how the kidneys take up contrast. If there is an area of scarring from a prior pyelo you may see decreased uptake of the dye in one aspect of the kidney. Also, you can see any discrepancies between the 2 kidneys in a relative fashion.
As for the anatomic component, it will show you signs of obstruction, possible stones, or tumors. It will show the ureters and then the bladder as well. It may pick up some bladder pathology, but that is typically reserved for a cystoscopy.
The VCUG gives you information about reflux, bladder shape/contour, and the bladder outlet during the voiding phase.
As for 1st studies to diagnose a pyelo, I'd first look at vitals, do a good physical exam and check a UA. You can typically diagnose a pyelo with those 3 tests. A CT isn't necessary to diagnose a garden variety pyelo.
