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What Is CO2 Blood Test?
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What Is CO2 Blood Test?

A CO2 blood test evaluates the amount of carbon dioxide in your bloodstream. If you have inadequate or too much carbon dioxide levels in blood, then you may have various health problems. Your doctor may recommend this CO2 test as a part of a metabolic panel. A metabolic panel comprises a group of tests that checks electrolytes and blood gases. Your doctor may refer to this test to check whether there is an imbalance between the oxygen and carbon dioxide in your blood. These imbalances indicate that you may have diseases like a kidney, respiratory, or metabolic disorder.

What Is CO2 Blood Test?

The cost of the carbon dioxide blood test is Rs.500 to Rs.1000, depending on your location and place.

Please check the price of the carbon dioxide test in Delhi/NCR, your nearby centers and other details.

Test Summary


Also known as CO2 content, carbon dioxide blood test, bicarbonate blood test, bicarbonate test, total CO2; TCO2; carbon dioxide content; CO2 content; bicarb; HCO3
Test Type Blood
Carbon dioxide test includes To check the levels of carbon dioxide in your blood
Preparation You may need to do fasting for 8-12 hours before the test. Also, inform your doctor whether you are taking medications like corticosteroids or antacids
Reporting Within 24 hrs
Test price The cost of the carbon dioxide blood test is Rs.500 to Rs.1000, depending on your location and place.
Also included in Health Insurance Plans
Related tests Bicarbonate test, HCO3 test, CO2 test serum


Your body has two major forms of CO2

  • HCO3 (bicarbonate, the main form of CO2 in the body)
  • PCO2 (carbon dioxide)


Why is the CO2 blood test recommended by your doctor?

Based on your symptoms, your doctor may refer to this test. Some popular signs of an imbalance of oxygen and carbon dioxide or a pH imbalance are:

  • Shortness of breath
  • Breathing difficulties
  • Nausea
  • Vomiting


These symptoms may indicate that you are having lung problems in the exchange between oxygen and carbon dioxide. If oxygen therapies are going on or you have gone through some surgeries, then you need to measure the carbon dioxide levels frequently.  

Do You Need Any Special Preparation for this CO2 Test?

You may need to do fasting for this test. Inform your doctor if you are taking medications like antacids or corticosteroids.

How A Blood Sample Is Collected for this CO2 Test?

For this test, your blood sample could be collected either from a vein or from an artery.

Venipuncture Blood Sample

In this type, your blood sample is taken from a vein. Your doctor will suggest a venipuncture blood test if he only wants to check HCO3.

For this test,

  • A healthcare provider cleans the site preferably the upper side of your arm with an antiseptic
  • Then, he may tie up an elastic band around your upper arm to identify the vein
  • He will insert the needle into the vein and collect your blood sample in a tube
  • Finally, he will remove the elastic band and the needle
  • A bandage or gauze will be placed at the puncture site


Arterial Blood Sample

Blood gas analysis is an integral part of the CO2 test. A blood gas analysis demands arterial blood because the gases and pH levels in the arteries may vary from venous blood.

Arteries transport oxygen throughout the body; on the other hand, veins carry deoxygenated blood to the lungs that are exhaled as carbon dioxide and excreted through the kidneys in the form of urine. Arterial blood collection is an intricate process and thus, this type of collection demands an experienced practitioner.

  • An expert cleans the site with a germ-killing antiseptic
  • He then inserts a needle into the artery and collects blood carefully
  • The collected sample is deposited in a tube until it is full
  • Then, he gently removes the needle
  • The person then applies pressure to the puncture site for at least five minutes to ensure the bleeding stops.
  • Then, he wraps the puncture site that you need to keep for at least an hour


The Interpretation of the Results

The normal range for CO2 is between 23 to 29 mEq/L (milliequivalent units per liter of blood).

This blood test also evaluates the pH of blood along with CO2 levels to find out the causes of your symptoms. Blood pH is either acidic or alkaline. Alkalosis is a condition when your body fluids are too alkaline. When your blood fluids are acidic, then it is called acidosis.

A blood pH measurement that is less than 7.35 is considered acidic. But when the blood pH measurement is greater than 7.45, then it is called alkaline.

Low Bicarbonate (HCO3)

A low bicarbonate condition (pH less than 7.35) is called metabolic acidosis. Common causes are

  • Kidney failure
  • Excessive diarrhea
  • Lactic acidosis
  • Seizures
  • Cancer
  • Lack of oxygen due to severe anemia, heart failure, or shock
  • Diabetic ketoacidosis (diabetic acidosis)


A test result of low bicarbonate and high pH (more than 7.45) is a condition known as respiratory alkalosis. Some popular causes are,

  • Hyperventilation
  • Fever
  • Pain
  • Anxiety

High bicarbonate (HCO3)

A test result of high bicarbonate and low pH (less than 7.35) is a condition known as respiratory acidosis. Common causes of this symptom are

  • Pneumonia
  • Asthma
  • Pulmonary fibrosis
  • Too much exposure to toxic chemicals
  • Tuberculosis
  • Lung cancer
  • Pulmonary hypertension
  • Too much obesity


A test result of high bicarbonate and high pH (more than 7.45) is a condition called metabolic alkalosis. Common causes of this symptom are,

  • Frequent vomiting
  • Inadequate potassium levels
  • Hypoventilation


1. What are the risks of the CO2 test?

This blood test involves minimal risks. Some of the symptoms that you may experience are,

      1. Excessive bleeding at the puncture site
      2. Dizziness
      3. Pain at the puncture site
      4. Site infection

2. What is respiratory alkalosis?

This condition happens when the levels of carbon dioxide and oxygen in the blood are not stable. In respiratory alkalosis, you breathe faster and deeper. As a result, the carbon dioxide levels drop drastically. This will uplift the pH of the blood and it becomes too alkaline.

3. What are hyperventilation and its causes?

Hyperventilation or over-breathing is the underlying cause of respiratory alkalosis. Causes of hyperventilation are,

      1. Heart attack
      2. Pain
      3. Asthma
      4. Overdosage of drugs
      5. Fever
      6. Infection
      7. Pregnancy
      8. Pulmonary embolism

4. How do you recover from respiratory alkalosis?

Your recovery treatment process may depend on the cause. If you are suffering from respiratory alkalosis due to conditions like anxiety, then you will recover completely. Once your carbon dioxide levels will increase, the symptoms will disappear utterly. Sometimes, this could be a medical emergency and your treatment depends on the underlying cause. 

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