Oral Cholecystogram
Medical Author:
Jay W. Marks, M.D.
Medical Editors:
Barbara K. Hecht,
Ph.D. and
Frederick Hecht, M.D.
What is an oral cholecystogram (OCG)?
The oral cholecystogram, or OCG, is a radiologic procedure for diagnosing
gallstones. An oral cholecystogram is in contrast to an intravenous cholangiogram (IVC).
How is an oral cholecystogram done?
For an OCG, the patient takes iodine-containing tablets by mouth for one night or two nights in a row. The iodine is absorbed from the intestine into the bloodstream, removed from the blood by the liver, and excreted by the liver into the bile. The iodine, together with the bile, is highly concentrated in the gallbladder. Iodine is used in an OCG because it is dense and radioopague (stops x-rays). It outlines the gallstones that are radiolucent (x-rays pass through them) and that are usually invisible on x-ray.
The bile ducts themselves cannot be seen on the x-ray in an OCG because the iodine is not concentrated in the ducts. Therefore, any gallstones lodged in the ducts will go undetected on OCG.
Failure to visualize the gallbladder on an OCG may occur for one of two reasons. First, a gallstone may have obstructed the cystic duct and prevented the iodine-containing bile from entering the gallbladder. Second, inflammation of the gallbladder -- usually due to gallstones -- may have interfered with the gallbladder's ability to concentrate bile and iodine. Whichever the cause, failure to visualize the gallbladder on an OCG strongly suggests a diseased gallbladder.
What are the risks of an oral cholecystogram?
The risks of an oral cholecystogram are few. One, of course, is the radiation. However, in an OCG there is a relatively small amount of radiation from the x-rays.
Another risk involves the iodine. Some people are allergic to iodine. Fortunately, most people who are allergic know that they are, and therefore do not undergo the test.
Next: When is an oral cholecystogram useful? »
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