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.
