Gastrin and Gastrin Stimulation Test

Gastrin and Gastrin Stimulation Test

Synonym/acronym: N/A.

Common use

To evaluate gastric production to assist in diagnosis of gastric disease such as Zollinger-Ellison syndrome and gastric cancer.

Specimen

Serum (1 mL) collected in a red- or red/gray-top tube.

Normal findings

(Method: Immunoassay)
AgeConventional UnitsSI Units (Conventional Units × 0.481)
0–1 mo70–190 pg/mL33.7–91.4 pmol/L
2 mo-15 yr55–185 pg/mL26.4–89 pmol/L
16 yr and olderLess than 100 pg/mLLess than 48.1 pmol/L
Values represent fasting levels.
Stimulation Tests
Gastrin stimulation test with secretin; 0.4 mcg/kg by IV bolusNo response or slight increase over baseline; increase of greater than 200 pg/ml above baseline is considered abnormal
Calcium may also be used as a stimulant.

Description

Gastrin is a peptide hormone produced by the G cells of the duodenum and pyloric antrum of the stomach. Gastrin is released into the blood in response to certain stimuli to include: vagal stimulation from the sight, smell or taste of food; the presence proteins and amino acids from partially digested food; alcohol; stomach distension; and hypercalcemia (as the main site of dietary calcium absorption is the duodenum). As blood levels of gastrin rise, gastrin is returned to the stomach to stimulate the parietal cells to secrete hydrochloric acid (gastric acid) for further digestion of food. At this point in the digestive process, gastrin also stimulates the chief cells of the stomach to secrete pepsinogen, increases antral muscle mobility, and promotes stomach contractions to stimulate gastric emptying. Gastrin also induces pancreatic secretions, gallbladder emptying, and release of intrinsic factor. Gastrin release is inhibited by the presence of acid in the stomach, somatostatin, glucagon and calcitonin. When enough gastric acid has been produced by the stomach, gastrin levels in the blood drop. Gastrin stimulation tests can be performed after a test meal or IV infusion of calcium or secretin.

This procedure is contraindicated for

    N/A

Indications

  • Assist in the diagnosis of gastric carcinoma, pernicious anemia, or G-cell hyperplasia
  • Assist in the diagnosis of Zollinger-Ellison syndrome
  • Assist in the differential diagnosis of ulcers from other gastrointestinal (GI) peptic disorders

Potential diagnosis

Increased in

  • Chronic gastritis (related to hypersecretion of gastrin, use of NSAIDs, or Helicobacter pylori infection)
  • Chronic renal failure (related to inadequate renal excretion)
  • Gastric and duodenal ulcers (related to hypersecretion of gastrin, use of NSAIDs, or H. pylori infection)
  • Gastric carcinoma (related to disturbance in pH favoring alkalinity, which stimulates gastrin production)
  • G-cell hyperplasia (hyperplastic G cells produce excessive amounts of gastrin)
  • Hyperparathyroidism (related to hypercalcemia; calcium is a potent stimulator for the release of gastrin)
  • Pernicious anemia (related to antibodies against gastric intrinsic factor [66% of cases] and parietal cells [80% of cases that affect the stomach’s ability to secrete acid; achlorhydria is a strong stimulator of gastrin production])
  • Pyloric obstruction (related to gastric distention, which stimulates gastrin production)
  • Retained antrum (remaining tissue stimulates gastrin production)
  • Zollinger-Ellison syndrome (gastrin-producing tumor)

Decreased in

    Hypothyroidism (related to hypocalcemia) Vagotomy (vagus nerve impulses stimulate secretion of digestive secretions; interruptions in these nerve impulses result in decreased gastrin levels)

Critical findings

    N/A

Interfering factors

  • Drugs and substances that may increase gastrin levels include amino acids, catecholamines, cimetidine, insulin, morphine, omeprazole, pantoprazole, sufotidine, terbutaline, calcium products, and coffee.
  • Drugs that may decrease gastrin levels include atropine, enprostil, glucagon, secretin, streptozocin, and tolbutamide.
  • In some cases, protein ingestion elevates serum gastrin levels.
  • Failure to follow dietary and medication restrictions before the procedure may cause the procedure to be canceled or repeated.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in diagnosing stomach disease.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s endocrine and gastrointestinal systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Note any recent procedures that can interfere with test results.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that multiple specimens will be collected and that each specimen collection takes approximately 5 to 10 min. Explain that pretest samples will be collected at 10 min and 1 min before administration of the stimulant. Poststimulation samples will be collected at 2, 5, 10, 15, 20, and 30 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues,  as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Instruct the patient to fast for 12 hr before the test. Instruct the patient to refrain from the use of chewing gum or tobacco products for at least 4 hr prior to and for the duration of the test. Protocols may vary among facilities.
  • Instruct the patient to withhold medications and alcohol for 12 to 24 hr, as ordered by the health-care provider (HCP).
  • Note that there are no fluid restrictions unless by medical direction.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

Intratest

  • Potential complications: N/A
  • Ensure that the patient has complied with dietary and medication restrictions and other pretesting preparations; ensure that food and medications have been withheld for at least 4 and 12 hr, respectively, prior to the procedure. The patient should be reminded to refrain from use of chewing gum or tobacco products during the test.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Administer gastrin stimulators as appropriate.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume usual diet and medications, as directed by the HCP.
  • Nutritional Considerations: Nutritional support with calcium, iron, and vitamin B12 supplementation may be ordered, as appropriate. Dietary modifications may include encouraging liquids and low-residue foods, eating multiple small meals throughout the day, and avoidance of foods that slow digestion such as foods high in fat and fiber. Severe cases of gastroparesis may require temporary treatments that include total parenteral nutrition or use of jejunostomy tubes.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Instruct the patient in the use of any ordered medications. Explain the importance of adhering to the therapy regimen. As appropriate, instruct the patient in the significant side effects and systemic reactions associated with the prescribed medication. Encourage him or her to review corresponding literature provided by a pharmacist.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include capsule endoscopy, CBC, CBC RBC indices, CBC RBC morphology, CBC WBC count and differential, esophagogastroduodenoscopy, fecal analysis, folate, gastric acid stimulation test, gastric emptying scan, H. pylori antibody, intrinsic factor antibodies, upper GI series, and vitamin B12.
  • Refer to the Endocrine and Gastrointestinal systems tables at the end of the book for related tests by body system.