In cases where patients experience no symptoms, gallstones are sometimes discovered as an incidental finding when imaging tests are conducted for another medical problem. When patients experience symptoms, gallstones may be diagnosed during a physical examination that includes a complete medical history.

A physician may perform several blood tests while diagnosing gallstones, usually to check for infection and the function of the liver and pancreatic enzymes. In most cases, imaging tests are used to diagnose gallstones. These imaging tests include:

• Ultrasound. An imaging technology that uses sound waves to produce images of the shape and outline of various tissues and organs of the body. Ultrasound is the imaging test most commonly used for gallstones. An abdominal ultrasound passes a special probe over the gallbladder and may show gallstones. In some cases, an endoscopic ultrasound (EUS) may be performed using an endoscope (lighted tube) inserted in the mouth to the small intestine because it produces better images than a standard ultrasound. EUS is useful for diagnosing gallstones within the bile ducts.
  
  
• X-rays. An image of a body part, organ or bodily system on film paper or fluorescent screens. It is produced by using low doses of radiation. X-rays are only useful in diagnosing gallstones, which contain enough calcium to be visible on an x-ray.
  
  
• Oral cholecystogram (OCG).  Test in which the patient swallows pills containing contrast dye before x-rays are taken. This test is useful in determining gallbladder function.
  
  
• Cholescintigraphy (HIDA scan). A small amount of a radioactive substance is injected intravenously (through a vein). The substance enters the liver and is secreted into bile. It identifies obstructions in the cystic duct and evaluates the ability of the gallbladder to contract.
  
  
• Endoscopic retrograde cholangiopancreatography (ERCP). This procedure is performed when gallstones are suspected in the bile ducts. An endoscope (lighted tube) is inserted through the mouth to the small intestine. A dye is passed through a thin flexible tube (catheter) inside the endoscope before x-rays are taken. ERCP can also be used to remove gallstones from the bile ducts in some cases.
  
  
• Magnetic resonance imaging (MRI). Tests, such as a magnetic resonance cholangiography or a magnetic resonance cholangiopancreatography (MRCP), may be performed instead of an ERCP because they are less invasive. An MRI uses powerful magnets to produce images on a computer screen.
  
  
• Gallbladder bile collection. When imaging tests do not reveal gallstones, but the patient is still experiencing symptoms, a sample of bile may be taken from the duodenum or bile duct during an ERCP or EUS. The bile is examined under a microscope to detect the presence of cholesterol or bile crystals, which may indicate that a small gallstone not detected with other tests is present.
  
  
• Computed axial tomography (CAT) scan. A test that allows for multiple x-rays to be taken from different angles around the patient. It creates images of organs and bones within the body. This may identify the presence of gallstones, but it is not as useful in identifying gallstones as other tests.