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Gastric pCO2–End-Tidal pCO2 Gap

Published: August 9, 2026Updated: August 17, 2026

Compares carbon dioxide in a gastric sample with exhaled end-tidal CO2 to help assess whether a feeding tube is in the stomach or airway.

Quick summary

["This comparison can help check feeding-tube placement, but it is interpreted together with the rest of the clinical assessment."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
60818-2
Short code
Gastric-ET pCO2 gap
Synonyms
Gastric-ET 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–end-tidal pCO2 gap compares the amount of carbon dioxide in material aspirated from the stomach with the carbon dioxide measured in exhaled breath. It is used mainly to help evaluate the placement of a feeding or nasogastric tube.

Why might I need this test?

A tube that enters the airway instead of the stomach can allow food or medication to be delivered into the lungs. Comparing gastric carbon dioxide with exhaled carbon dioxide provides additional information about the contents of the aspirated sample and the likely location of the tube.

How is the test performed?

A clinician may aspirate fluid through a feeding or nasogastric tube while end-tidal carbon dioxide is measured from the patient's breath using capnography. The two carbon dioxide measurements are then compared.

How do I prepare for the test?

Fasting is not usually required for this comparison. Follow the instructions given for tube placement or use, and tell the care team about breathing difficulty, coughing, or trouble with feeding. Do not reposition or remove the tube yourself.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

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–end-tidal CO2 gap

Frequently asked questions

Is this the same as a blood-gas test?
No. It compares carbon dioxide from a gastric sample with carbon dioxide measured in exhaled breath, rather than testing a blood sample.
Does the result prove where my feeding tube is?
No. It is an additional placement check, and an unexpected result may lead to further testing rather than proving malposition by itself.
What if I feel coughing or breathing trouble during feeding?
Stop feeding and contact the care team promptly. These symptoms may indicate aspiration or possible airway placement and need prompt assessment.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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