An intravenous pyelogram (IVP
) is a radiological examination
of the kidney
collecting system, ureter
s, and bladder
. It involves taking serial x-ray
s of the abdomen
before and after the intravenous
administration of a contrast agent
. The contrast travels through the bloodstream to the kidneys, where it is filtered out of the blood by the renal parenchyma
. The contrast then flows into the renal collecting system, down the ureters, and into the bladder. Proper timing of the radiological images will demonstrate the anatomy of the urinary system, provide an indication of the physiological functioning of the kidney, and reveal a variety of urological disorder
While several disorders historically diaganosed by IVP are now revealed through the use of CT scans, ultrasound studies, or MRI exams, there remain several indications for this examination. The most common signs and symptoms that an IVP is used to evaluate are flank pain, blood in the urine, and abnormal frequency of urination (either too often or not often enough).
Prior to the examination, a blood test will be performed to assess the levels of certain molecules (BUN and creatinine) that are indicators of renal function (this will determine the patient's ability to clear the contrast agent from the body after the exam). The patient will be asked to refrain from eating after midnight the night before and may be given a laxative; this will help to decrease the potential obstruction of the urinary system by overlying intestinal gas or feces. A brief medical history will be taken to discern whether the patient has had a previous reaction to intravenous iodine, a thyroid condition (the thyroid processes iodine in the body), or asthma or an allergy to shellfish. (The contrast dye is an iodinated liquid and a very small percentage of the population may have an allergic reaction to exogenous iodine; in these cases, an antihistamine may be given prior to the injection and a contrast agent with a lower osmolarity will be used - lower osmolarity contrast agents are about ten times more expensive than the higher osmolarity agents. People with asthma are more susceptible to allergic reactions of all sorts.)
The examination begins with a plain x-ray of the abdomen. This "scout" film will be reviewed by the radiologist prior to the injection of the contrast. Factors that will be considered include the visibility of the urinary system (the area may be obscured by barium from a previous radiological examination, or by gas or feces as described above), the positioning of the patient with respect to the x-ray machine, and the presence of any radio-opaque kidney stones in the region of the urinary system. After the plain film has been read and cleared, the contrast will then be injected into a vein in the arm and an x-ray of the kidney region will be taken after one minute. This first film should demonstrate the anatomy of the kidneys as the dye is filtered from the blood. Another film is taken at three minutes post-injection; this should demonstrate the upper collecting system (the calyces and renal pelvis). At five minutes, an image may be taken of the entire abdominal region as the contrast should begin to flow down the ureters. At fifteen minutes, the bladder should begin to fill; it is usually full by the time the 30-minute x-ray is taken. The patient will then void the urine and a post-void film will be taken of the bladder.
Examples of Diagnostic Findings
- Obstruction of the urinary system will result in dilatation of portions of the urinary tract proximal to the location of the obstruction. Obstructions include kidney stones, an enlarged prostate gland, and abdominal masses compressing the ureters.
- Filling defects in the bladder may represent a tumor, blood clots, or non-opaque kidney stones.
- Congenital anomalies may be revealed: ectopic kidneys, duplicated ureters, and bladder diverticula are usually incidental findings.
Cases have been reported in which patients have passed their kidney stones during the procedure while they were still in the radiology suite or shortly after the IVP was performed. It is thought that this may be a result of the osmotic diuresis caused by the administration of the contrast agent.