Gastrin Test: Meaning, High Levels, Functions & Normal Ranges

Overview

The Gastrin Test is a blood test used to measure the amount of the hormone gastrin in the bloodstream. Gastrin is produced by the stomach and plays an essential role in digestion by stimulating the production of stomach acid (hydrochloric acid or HCl).

Doctors usually recommend this test when they suspect disorders related to excess acid production, gastrin-secreting tumors, or conditions affecting the stomach lining. It is commonly used to diagnose:

• Zollinger–Ellison syndrome
• Gastrinoma (gastrin-secreting tumor)
• Chronic gastritis
• Pernicious anemia
• Peptic ulcers
• Conditions causing abnormal stomach acid levels

The Gastrin Test is primarily performed in a fasting state because food naturally increases gastrin levels.

Where Is Gastrin Produced in the Body?

Gastrin is produced mainly by specialized cells called G-cells located in:

1. The Stomach

• Especially in the antrum, the lower part of the stomach
• Gastrin from this area helps control stomach acid release

2. The Duodenum

• A smaller amount of gastrin is produced in the upper portion of the small intestine

These G-cells release gastrin in response to:

• Eating food
• Stomach stretching
• Certain nutrients like proteins
• Low stomach acid levels

Once released, gastrin travels through the bloodstream to the stomach, signaling it to produce more acid.

Main Functions and Importance of Gastrin

Gastrin is one of the most important hormones for digestive health.

1. Stimulates Gastric Acid Production

Gastrin tells the stomach to release hydrochloric acid (HCl), which:

• Breaks down food
• Activates digestive enzymes
• Helps destroy harmful microorganisms

2. Promotes Protein Digestion

Stomach acid helps digest proteins by activating an enzyme called pepsin.

3. Helps Maintain Acidic pH

A properly acidic environment ensures:

• Smooth digestion
• Prevention of bacterial overgrowth
• Proper absorption of minerals

4. Supports Normal Stomach Motility

Gastrin helps regulate:

• Stomach contractions
• Movement of food from stomach to intestine

Causes of Low / Negative Gastrin Levels

Low gastrin levels are less common but may occur for the following reasons:

1. Stomach Surgery (Gastrectomy)

Removal of part or all of the stomach reduces or eliminates gastrin-producing cells.

2. Atrophic Gastritis

Damage to the stomach lining reduces the number of G-cells.

3. Hypochlorhydria

Reduced stomach acid leads the body to slow down gastrin release rather than increase it.

4. Long-Term Antacid or PPI Use

Medicines such as:

• PPIs (Omeprazole, Pantoprazole, Esomeprazole)
• H2 blockers (Ranitidine, Famotidine)

inhibit acid production and can disrupt gastrin regulation.

Symptoms of Low / Negative Gastrin Levels

Symptoms usually relate to poor digestion, not the low gastrin itself.

• Indigestion and bloating
• Early fullness
• Poor protein digestion
• Vitamin B12 deficiency
• Iron deficiency
• Fatigue due to malabsorption
• Nausea

Causes of High / Positive Gastrin Levels

High gastrin levels indicate overproduction of the hormone.

This can be caused by:

1. Zollinger–Ellison Syndrome

A condition where a gastrinoma tumor in the pancreas or duodenum produces excess gastrin.

2. Chronic Atrophic Gastritis

When the stomach lining is damaged, acid levels drop, and the body compensates by increasing gastrin.

3. Pernicious Anemia

Autoimmune destruction of stomach cells leads to:

• Low stomach acid
• Vitamin B12 deficiency
• High gastrin levels

4. Helicobacter pylori Infection

This bacteria affects acid regulation, causing high gastrin.

5. Kidney Failure

Kidneys help clear gastrin from the blood—reduced clearance raises gastrin levels.

6. Long-Term PPI Use

When PPIs suppress acid, the body produces extra gastrin to balance acid levels.

Symptoms of High / Positive Gastrin Levels

Symptoms depend on the underlying cause but commonly include:

1. Peptic or Recurrent Ulcers

Due to excess acid damaging stomach or duodenal lining.

2. Severe Abdominal Pain

Especially in Zollinger–Ellison syndrome.

3. Acid Reflux (GERD)

Burning sensation in the chest due to excessive acid.

4. Diarrhea

High acid entering the intestine disrupts normal digestion.

5. Weight Loss

May indicate a tumor or chronic ulceration.

Reference Ranges

Values depend on fasting status, medications, and stomach conditions.

Sample Type

The test requires:

• Blood sample (serum)
• Collected after overnight fasting (8–12 hours)

Patients should avoid certain medications temporarily if possible.

Test Preparation

• Fast for 8–12 hours before the test
• Avoid the following before testing (if doctor allows):
  • PPIs for 1 week
  • H2 blockers for 48 hours
  • Antacids for several hours
• Avoid smoking before the test
• Inform doctor about:
  • Ulcer history
  • PPI/H2 blocker use
  • Recent endoscopy
  • Any stomach surgery

When to Consult a Doctor

You should see a doctor if you experience:

• Frequent or recurrent ulcers
• Severe abdominal pain
• Unexplained weight loss
• Persistent acid reflux
• Chronic diarrhea
• Symptoms of pernicious anemia
• Frequent nausea or vomiting

Also seek medical advice if you have:

• Sudden worsening of ulcer symptoms
• Black or tarry stools
• Vomiting blood (medical emergency)

Important Word Explanations

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