Gastric pCO₂ Gap (Gastric-to-Arterial Carbon Dioxide Pressure Difference)
A specialized measurement comparing carbon dioxide pressure in the stomach with arterial blood to help assess gastric blood flow and oxygenation.
["An elevated gastric pCO₂ gap may indicate reduced stomach blood flow or tissue oxygenation, particularly in critically ill patients."]
Key facts at a glance
- LOINC
- 60817-4
- Short code
- Gastric-art pCO2 gap
- Synonyms
- Gastric-art pCO2 gap
- Category
- liver
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 10
- Ref high
- 40
- Critical range
- — – 500 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- gastric-tonometry
- CPT
- 84484
- SNOMED
- 302774002
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What is this test?
The gastric pCO₂ gap is the difference between carbon dioxide partial pressure measured in the stomach or gastric tissue and the arterial pCO₂ measured in blood. It is a specialized test used mainly in critical care to help evaluate stomach blood flow and tissue oxygenation.
Why might I need this test?
This test may be ordered when a patient has low blood pressure, shock, sepsis, or other conditions that could reduce blood flow to the stomach. It may be used alongside other findings to assess possible gastric mucosal hypoperfusion, which can contribute to stress-related stomach injury.
How is the test performed?
Carbon dioxide is measured in the stomach, often through a specialized gastric tube or sensor, and an arterial blood gas is used to determine the arterial pCO₂. The difference between these measurements is then calculated.
How do I prepare for the test?
This test is generally performed in a hospital or intensive care setting. Follow your care team's instructions about fasting, medications, and procedures, and tell the team if you have any known bleeding or blood-clotting risks.
Reference range
Adult: 10-40 U/LN/A
No special preparation required. Avoid fatty meals before the test if possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Gastric pCO₂ gap
Frequently asked questions
What does an elevated gastric pCO₂ gap mean?
Is this the same as an arterial blood gas test?
Can this test diagnose stomach ulcers or bleeding?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy