Measurement of serum gastrin levels, which is accomplished through radioimmunoassay techniques, is indicated when disorders producing elevated levels are suspected. Excessive gastrin secretion occurs because of normal feedback mechanisms in disorders associated with decreased gastric acid production as a result of cellular destruction or atrophy (e.g., gastric carcinoma and age-related changes in gastric acid secretion). Elevated levels also may be seen in gastric and duodenal ulcers, in which gastric acid secretion is actually normal or low; pernicious anemia; uremia; and chronic gastritis. Decreased gastrin levels are associated with true gastric hyperacidity as may occur with stress ulcers.

Both protein ingestion and calcium infusions elevate serum gastrin levels in certain situations. Thus, these substances can be used to provoke gastrin secretion when a single serum determination is inconclusive. In the secretagogue provocation test, a fasting serum gastrin sample is drawn and the client is then given a high-protein test meal. A postprandial blood sample is then obtained. In individuals with duodenal or gastric ulcers, gastrin levels will be markedly higher than in normal persons after protein-stimulated gastrin secretion. Likewise, an infusion of calcium gluconate produces elevated serum gastrin levels in a person with gastrinoma caused by gastrin production by tumor cells. This effect is not seen in individuals with peptic ulcer disease.

Note: Postprandial values may vary according to the test method used.

• Protein ingestion and calcium infusions will elevate serum gastrin levels in some situations; these substances may be used for "challenge tests" of gastrin secretion.

• Suspected gastrinoma (Zollinger-Ellison syndrome) as indicated by markedly elevated levels (e.g., greater than 1000 pg/mL) and by marked response to calcium challenge
• Support for diagnosing gastric carcinoma, pernicious anemia, or G-cell hyperplasia as indicated by elevated levels
• Differential diagnosis of peptic ulcer disease from other disorders, because gastrin levels may be normal but will rise in response to protein challenge

Nursing Care Before the Procedure

General client preparation is the same as that for any test involving collection of a peripheral blood sample (see Appendix I).

• For this test, the client should fast from food for 12 hours before the study. Water is not restricted. It also is recommended that medications be withheld for 12 to 24 hours before the test, although this practice should be confirmed with the person ordering the study.

A venipuncture is performed and the sample collected in a red-topped tube. The sample should be packed in ice, handled gently to avoid hemolysis, and transported immediately to the laboratory.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any test involving the collection of a peripheral blood sample.

• Resume usual diet and medications.
• Complications and precautions: Assess bowel sounds if levels are increased to 100 to 500 pg/mL, which indicates Zollinger-Ellison syndrome associated with peptic ulcer disease.