DIAGNOSTIC AIDS IN GASTRIC DISORDERS: GASTRIC EMPTYING SCINTIGRAPHY
Gastric emptying can be assessed by several methods: scintigraphy, breath testing, and motility capsule testing. Gastric emptying scintigraphy has been the classic test for measuring gastric emptying of a radiolabeled meal. It is quantitative and physiologic. It is used to assess for gastric emptying disorders (either slow or rapid) in a symptomatic patient (in whom structural or mucosal disorders are often ruled out with upper endoscopic or upper gastrointestinal radiologic studies). It is primarily used to diagnose gastroparesis in a patient who has symptoms of this disorder, such as nausea, early satiety, and postprandial fullness. The test can also assess for rapid gastric emptying, which is seen in the dumping syndrome.
The 99mtechnetium sulfur colloid radiolabeled meal consists of a standardized meal (the equivalent of two large eggs plus two slices of bread with jam and water). The radiolabel needs to be cooked into the egg white, so that the radioisotope binds to the solid phase of the test meal. Imaging is performed after meal ingestion with a gamma counter with the patient in the anterior and posterior projections at four time points (0, 1, 2, and 4 hours). Performing scintigraphy over 4 hours helps to detect delayed gastric emptying.
The simplest approach for interpreting gastric emptying studies is to report the percentage of retention at defined times after meal ingestion (usually at 2 and 4 hours). Curve-fitting techniques can calculate the half-emptying time, the time for half of the stomach contents to have emptied from the stomach. Other parameters of potential use are the lag phase for solids, which represents the time required for trituration of solid food into 1- to 2-mm particles that can then empty through the pylorus.
Measurement of gastric emptying of solids is more sensitive than measurement of gastric emptying of liquids for detection of symptomatic gastroparesis (slow gastric emptying) because emptying of liquids is often preserved until the gastroparesis is advanced. In patients who have undergone gastric surgery, a dual solid and liquid emptying test may be helpful because symptoms may result from slow solid emptying or rapid liquid emptying.
Hyperglycemia, smoking, and medications are factors that affect gastric emptying. Marked hyperglycemia with serum glucose levels of 250 mg/dL or more significantly delays gastric emptying in diabetic patients when compared with euglycemia. Blood glucose should be under reasonable control on the day of an emptying test to obtain a reliable measurement of gastric emptying. Smoking during the test can delay gastric emptying. Medications, primarily opiate narcotic analgesics and anticholinergic medications, can delay gastric emptying. It is best to stop these medications for 2 days prior to and during the test to get a reliable assessment of gastric emptying.