An intravenous pyelogram or IVP is a radiological procedure used to visualise disturbances of the urinary system, including the kidneys, ureters, and bladder.

It is done as a series of X-rays before and after a contrast agent is injected into a vein. This contrast is removed from the blood by the kidneys at a predictable time, where they initially appear opaque on X-ray film early after injection, followed by the appearance of iodinated contrast in the urine which outlines the renal calyces, ureters and bladder in the later X-rays in the series. Finally the bladder is imaged while filled and then after emptying, allowing assessment of any unseen abnormalities and completeness of voiding.

Functional information can be obtained both in a general sense and comparing one kidney to the other. The anatomy of the kidneys and collecting system can be observed. The exact point of a blockage (eg, from stone or tumor) can often be precisely identified.

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• KUB