How are gallstones diagnosed? (Part 5)
Liver and pancreatic blood tests
When the liver or pancreas becomes inflamed or their ducts become obstructed and enlarged, the cells of the liver and pancreas release some of their enzymes into the blood. The most commonly-measured liver enzymes in blood are aspartate aminotransferase (AST) and alanine aminotransferase (ALT). The most commonly-measured pancreatic enzymes in blood are amylase and lipase. Many medical conditions that affect the liver or pancreas cause these blood tests to become abnormal, so these abnormalities alone cannot be used to diagnose gallstones. Nevertheless, abnormalities of these tests suggest there is a problem with the liver, bile ducts, or pancreas, and gallstones are a common cause of such abnormal tests, particularly during sudden obstruction of the bile ducts or pancreatic ducts. Thus, abnormal liver and pancreatic blood tests direct attention to the possibility that gallstones may be causing the acute problem.
Duodenal biliary drainage
Duodenal biliary drainage is a procedure that occasionally can be useful in diagnosing gallstones; however, it is not often used. As previously discussed, gallstones begin as microscopic particles of cholesterol or pigment that grow in size. It is clear that some people who develop biliary colic, cholecystitis, or pancreatitis have only these particles in their gallbladders, yet the particles are too small to obstruct the ducts. There are two potential explanations for how obstruction might occur in this situation. The first is that a small gallstone initially caused an obstruction before passing through the bile ducts into the intestine. The second is that particles passing through the bile ducts can "irritate" the ducts, causing spasm of the muscle within the walls of the ducts (which obstructs the flow of bile) or inflammation of the duct that causes the wall of the duct to swell (and also obstructs the duct).
- For duodenal drainage, a thin plastic or rubber tube with several holes at its tip is passed through a patient's anesthetized nostril, down the back of the throat, through the esophagus and stomach, and into the duodenum where the bile and pancreatic ducts enter the small intestine. This is done with the help of x-ray (fluoroscopy).
- Once the tube is in place, a synthetic hormone related to cholecystokinin, the hormone that is normally released after a meal to cause the gallbladder, is injected intravenously. As a result, the gallbladder contracts and squeezes out its concentrated bile into the duodenum.
- The bile is sucked through the tube in the duodenum and examined for the presence of small cholesterol and pigment particles under a microscope.
The risks to the patient of duodenal drainage are minimal. (There have been no reports of reactions to the synthetic hormone.) Nevertheless, duodenal drainage is uncomfortable.
A modification of duodenal drainage involves collection of bile through an endoscope at the time of an upper gastrointestinal endoscopy-either esophago-gastro-duodenoscopy (EGD) or ERCP.
Oral cholecystogram (OCG)
The oral cholecystogram or OCG is a radiologic (X-ray) procedure for diagnosing gallstones.
- The patient takes iodine-containing tablets for one or two nights in a row and then has an X-ray of the abdomen.
- The iodine is absorbed from the intestine into the blood, removed from the blood by the liver, and excreted into bile.
- In the gallbladder, the iodine becomes concentrated along with the bile.
- On the X-ray, the iodine, which is dense and stops X-rays, fills the gallbladder and outlines the gallstones which are not dense, and allow X-rays to pass through them. The ducts cannot be seen on the x-ray because the iodine is not concentrated in the ducts.
The OCG is an excellent procedure for diagnosing gallstones; it finds 95% of them. The OCG has been replaced, however, by ultrasonography because ultrasonography is slightly better at finding gallstones and can be done immediately without waiting one or two days for the iodine to be absorbed, excreted, and concentrated.
Unlike ultrasonography, the OCG also cannot give information about the presence of non-gallstone related diseases. As would be expected, ultrasonography sometimes finds gallstones that are missed by the OCG. Less frequently, the OCG finds gallstones that are missed by ultrasonography. For this reason, if there is a strong suspicion that gallstones are present but ultrasonography does not show them, it is reasonable to consider doing an OCG; however, EUS has mostly replaced the OCG in this situation. An OCG should not be done in individuals who are allergic to iodine.
Intravenous cholangiogram (IVC)
The intravenous cholangiogram or IVC is a radiologic (X-ray) procedure that is used primarily for looking at the larger intrahepatic and the extrahepatic bile ducts. It can be used to locate gallstones within these ducts.
An iodine-containing dye is injected intravenously into the blood. The dye is removed from blood by the liver and excreted into bile. Unlike the iodine used in the OCG, the iodine in the IVC is concentrated sufficiently enough in the bile ducts to outline the ducts and any gallstones within them. The IVC is rarely used because it has been replaced by MRI cholangiography and endoscopic ultrasound. Moreover, occasional serious reactions to the iodine-containing dye can occur, which rarely may result in the death of the patient.