Gastric Analysis and Gastric Acid Stimulation Test

Gastric Analysis and Gastric Acid Stimulation Test

Synonym/acronym: N/A.

Common use

To evaluate gastric fluid and the amount of gastric acid secreted toward diagnosing gastrointestinal disorders such as ulcers, cancers, and inflammation.

Specimen

Gastric fluid collected in eight plastic tubes at 15-min intervals.

Normal findings

(Method: Volume measurement and pH by ion-selective electrode)
Basal acid output (BAO)Male: 0–10.5 mmol/hr
Female: 0–5.6 mmol/hr
Peak acid output (PAO)Male: 12–60 mmol/hr
Female: 8–40 mmol/hr
Peak response timePentagastrin, intramuscular: 15–45 min
Pentagastrin, subcutaneous: 10–30 min
BAO/PAO ratioLess than 0.2

Description

Gastric fluid is evaluated macroscopically for general physical and chemical characteristics such as color, presence of mucus or blood, and pH; gastric fluid is also evaluated microscopically for the presence of organisms and abnormal cells. The normal appearance of gastric fluid is a translucent, pale gray, slightly viscous fluid containing some mucus but not usually blood. pH is usually less than 2 and not greater than 6. Organisms are usually absent in gastric fluid owing to the acidic pH.

The gastric acid stimulation test is performed to determine the response to substances administered to induce increased gastric acid production. Pentagastrin is the usual drug of choice to induce gastric secretion because it has no major side effects. The samples obtained from gastric acid stimulation tests are examined for volume, pH, and amount of acid secreted. First, basal acid output (BAO) is determined by averaging the results of gastric samples collected before the administration of a gastric stimulant. Then a gastric stimulant is administered and peak acid output (PAO) is determined by adding together the gastric acid output of the highest two consecutive 15-min stimulation samples. Finally, BAO and PAO are compared as a ratio, which is normally less than 0.2.

This procedure is contraindicated for

  • high alert Patients with esophageal varices, diverticula, stenosis, malignant neoplasm of the esophagus, aortic aneurysm, severe gastric hemorrhage, and congenital heart failure.
  • high alert Patients with a history of asthma, paroxysmal hypertension, urticaria, or other allergic conditions should not be administered histamine diphosphate.

Indications

  • Detect duodenal ulcer
  • Detect gastric carcinoma
  • Detect pernicious anemia
  • Detect Zollinger-Ellison syndrome
  • Evaluate effectiveness of vagotomy in the treatment of peptic ulcer disease

Potential diagnosis

Increased in

  • Any alteration in the balance between the digestive and protective functions of the stomach that increases gastric acidity, such as hypersecretion of gastrin, use of NSAIDs, or Helicobacter pyloriinfection.

    • Appearance

  • Color
    • Yellow to green indicates the presence of bile (related to obstruction in the small intestine distal to the ampulla of Vater)
    • Pink, red, brown indicates the presence of blood (related to some type of gastric lesion evidenced by ulcer, gastritis, or carcinoma)
  • Microscopic evaluation
    • Red blood cells (related to trauma or active bleeding)
    • White blood cells (related to inflammation of the gastric mucosa, mouth, paranasal sinuses, or respiratory tract)
    • Epithelial cells (related to inflammation of the gastric mucosa)
    • Malignant cells (related to gastric carcinoma)
    • Bacteria and yeast (related to conditions such as pyloric obstruction, pulmonary tuberculosis)
    • Parasites (related to parasitic infestation such as Giardia, H. pylori,hookworm, or Strongyloides)

    • Increased Gastric Acid Output

  • BAO
    • Basophilic leukemia
    • Duodenal ulcer
    • G-cell hyperplasia
    • Recurring peptic ulcer
    • Retained antrum syndrome
    • Systemic mastocytosis
    • Vagal hyperfunction
    • Zollinger-Ellison syndrome
  • PAO
    • Duodenal ulcer
    • Zollinger-Ellison syndrome

Decreased in

    Conditions that result in the gradual loss of function of the antrum and G cells, where gastrin is produced, will reflect decreased gastrin levels.

    Decreased Gastric Acid Output

    BAO
    • Gastric ulcer
    PAO
    • Chronic gastritis
    • Gastric cancers
    • Gastric polyps
    • Gastric ulcer
    • Myxedema
    • Pernicious anemia

Critical findings

    N/A

Interfering factors

  • Drugs that may increase gastric volume include atropine, diazepam, ganglionic blocking agents, and insulin.
  • Drugs and substances that may increase gastric pH include caffeine, calcium salts, corticotropin, ethanol, rauwolfia, reserpine, and tolazoline.
  • Drugs and substances that may decrease gastric pH include atropine, cimetidine, diazepam, famotidine, ganglionic blocking agents, glucagon, nizatidine, omeprazole, oxmetidine, propranolol, prostaglandin F2a, ranitidine, and secretin.
  • Failure to follow dietary restrictions may result in stimulation of gastric secretions.
  • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.
  • Exposure to the sight, smell, or thought of food immediately before and during the test may result in stimulation of gastric secretions.

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 procedure can assist in diagnosing disease and inflammation in the stomach and upper intestine.
  • 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 gastrointestinal system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • 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 specimen collection takes approximately 60 to 120 min. Address concerns about pain and explain that some discomfort is experienced from insertion of the nasogastric tube.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Drugs and substances that may alter gastric secretions (e.g., alcohol, histamine, nicotine, adrenocorticotropic steroids, insulin, parasympathetic agents, belladonna alkaloids, anticholinergic drugs, histamine receptor antagonists) should be restricted by medical direction for 72 hr before the test.
  • Instruct the patient to fast from food after the evening meal the night before the test and not to drink water for 1 hr before the test. Instruct the patient to refrain from the use of chewing gum or tobacco products for at least 12 hr prior to and for the duration of the test. Protocols may vary among facilities.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

Intratest

  • Potential complications:

  • Complications may include improper insertion of the gastric tube, bleeding, esophageal perforation, and laryngospasm.

  • Ensure that the patient has complied with dietary restrictions and other pretesting preparations; ensure that food has been restricted for at least 12 hr prior to the procedure.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Ensure that the patient does not have a history of asthma, paroxysmal hypertension, urticaria, or other allergic conditions if histamine diphosphate is being considered for use in the test.
  • Record baseline vital signs.
  • Have the patient remove dentures if the patient is wearing them.
  • Ask the patient to sit, or help the patient recline on the left side.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • 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.
  • A cold lubricated gastric (Levine) tube is inserted orally. Alternatively, if the patient has a hyperactive gag reflex, the tube can be inserted nasally. The tube must have a radiopaque tip.
  • Fluoroscopy or x-ray is used to confirm proper position of the tube before the start of the test.
  • Using a constant but gentle suction, gastric contents are collected. Do not use specimens obtained from the first 15 to 30 min of suctioning.
  • The gastric stimulant is administered, and the peak basal specimens are collected over a 60-min period as four 15-min specimens. Number the specimen tubes in the order in which they were collected.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be sent to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Instruct the patient to resume usual diet and medication, as directed by the HCP.
  • Monitor vital signs and neurological status every 15 min for 1 hr, then every 2 hr for 4 hr, and then as ordered by the HCP for evaluation. Protocols may vary among facilities.
  • Instruct the patient to report any chest pain, upper abdominal pain, pain on swallowing, difficulty breathing, or expectoration of blood. Report these to the HCP immediately.
  • Monitor for side effects of drugs administered to induce gastric secretion (e.g., flushing, headache, nasal stuffiness, dizziness, faintness, nausea).
  • 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.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • 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 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, endoscopy sinus, esophagogastroduodenoscopy, fecal analysis, folate, gastric emptying scan, gastrin, H. pylori antibody, intrinsic factor antibodies, upper GI series, and vitamin B12.
  • Refer to the Gastrointestinal System table at the end of the book for related tests by body system.