TCO2: Definition, Indications, Preparation, Procedure, Results and Outlook

A carbon dioxide blood test measures the amount of carbon dioxide (CO2) in the blood serum.

We are talking about the liquid part of the blood. A carbon dioxide test may also be called:

  • A test for total carbon dioxide (TCO2).
  • A full carbon dioxide test.
  • Baking soda test.
  • A test for bicarbonate (HCO3-).
  • A carbon dioxide test serum.

You may receive a carbon dioxide test as part of a metabolic panel. A metabolic panel is a group of tests that measure electrolytes and gases in the blood.

The body contains two main forms of carbon dioxide:

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

Your doctor can use this test to determine if there is an imbalance between oxygen and carbon dioxide in your blood or a pH imbalance. These imbalances can be signs of a kidney, respiratory, or metabolic disorder.

Bicarbonate is a chemical that acts as a buffer and does not allow the pH of the blood to become too acidic or too basic. The kidney and lungs balance the levels of bicarbonate in the body.

If the bicarbonate levels are too high or too low, it could indicate a problem with those organs.


Therefore, the bicarbonate test helps detect several conditions that affect bicarbonate levels in the blood, such as lung diseases, kidney disorders, and metabolic requirements.

Why take the exam?

It is ordered to discover, control, or treat many different serious diseases that have been associated with a change in the acid-base balance of the body.

Most of the carbon dioxide [CO2] found in the body comes in the form of HCO3, which is called bicarbonate.

It would be fair to say that the carbon dioxide (TCO2) whole blood test measures bicarbonate levels. It can be done under the following conditions:

  • As part of a routine exam or to help evaluate chronic or acute illness.
  • Detect and assess an electrolyte imbalance.
  • To monitor the effectiveness of treatment for known imbalances.
  • At different intervals to help manage conditions like kidney disease and high blood pressure.
  • To assess your body’s acid-base (pH) balance.
  • As part of the electrolyte panel, along with other tests such as the sodium, potassium, and chloride test.

Understanding Total Carbon Dioxide Results

The highest values ​​are found in the blood of people suffering from persistent vomiting and dehydration or those who have just received a blood transfusion. Overuse of antacids can also increase your bicarbonate level.

It can also indicate conditions such as chronic obstructive pulmonary disease, heart disease, Cushing’s disease, and Crohn’s syndrome.

Low bicarbonate values ​​are seen due to rapid breathing and an overdose of alcohol or aspirin.

Severe malnutrition, burns, shock, liver or kidney disease, hyperthyroidism, uncontrolled diabetes, or a massive heart attack can also lower bicarbonate value.

A reference range is a set of values ​​that helps the healthcare professional interpret a medical examination.

It can vary with age, gender, and other factors. Reference ranges may also vary between laboratories, in value, and units depending on the instruments used and the method of establishing the reference ranges.

The total carbon dioxide (TCO2) blood test is usually ordered as part of a complete metabolic panel. It can also be called part of a panel to measure electrolyte levels.

When there are changes in the levels of bicarbonate within the body, it indicates that someone could be retaining too many fluids or not able to retain enough fluids.

These changes cause electrolyte levels to become unbalanced, and a positive total carbon dioxide (TCO2) blood test will result.

If there is a suspicion that the lung or kidney functions are inadequate, this blood test can be ordered independently to determine a diagnosis.

This is because the kidneys are one of the primary organs that help regulate bicarbonate levels in the body.

A panel can also be independently requested to determine if a treatment plan is effective.

A typical test result is 23 to 29 milliequivalents per liter [mEq / L].

Your doctor will order a carbon dioxide blood test based on your symptoms. Signs of an oxygen and carbon dioxide imbalance or a pH imbalance include:

  • Short of breath.
  • Other breathing difficulties.
  • Nausea.
  • Vomiting

These symptoms may point to lung dysfunction that involves the exchange between oxygen and carbon dioxide.

You will need to have your blood oxygen and carbon dioxide levels checked if you are on oxygen therapy or have certain surgeries.

How to take a blood sample

Blood samples for a carbon dioxide blood test can be taken from a vein or an artery.

To obtain the blood for this blood test, a vein is usually drawn from the elbow or the back of the hand.

If a vein cannot be located or is not viable in these locations, the laboratory technician may recommend other blood collection methods.

You may need to modify the medications or supplements taken before the blood draw.

Your doctor will tell you which medications to avoid for the blood test and how long this should take. Do not change the medication you are taking without talking to your doctor.

Venipuncture blood sample

Venipuncture is the term used to describe a basic blood sample taken from a vein. Your doctor will order a simple venipuncture blood sample if they want to measure bicarbonate (HCO3-).

To obtain a venipuncture blood sample, a healthcare provider:

  • Clean the site (often the inside of the elbow) with a germ-killing antiseptic.
  • Wrap an elastic band around the upper arm to make the vein swell with blood.
  • Gently insert a needle into the vein and collect the blood in the attached tube until complete.
  • Remove the elastic band and needle.
  • Cover the puncture wound with sterile gauze to stop any bleeding.

Arterial blood sample

Blood gas analysis is often a part of the carbon dioxide test. A blood gas test requires arterial blood because the gases and pH levels in the arteries are different from venous blood (blood from a vein).

The arteries carry oxygen throughout the body. The veins carry metabolic waste and deoxygenated blood to the lungs to be exhaled as carbon dioxide and the kidneys to pass through the urine.

This more complicated procedure is performed by a professional trained to access the arteries safely.

Arterial blood is usually taken from an artery called the radial artery in the wrist. This is the main artery in line with your thumb, where you can feel your pulse.

Or, blood can be drawn from the brachial artery in the elbow or the femoral artery in the groin. To obtain an arterial blood sample, the practitioner:

Clean the site with a germ-killing antiseptic. Gently insert a needle into the artery and draw blood into an attached tube until it is full. Remove the needle.

Apply pressure firmly to the wound for at least five minutes to ensure the bleeding stops. (Arteries carry blood at higher pressures than veins, so it takes longer for blood to form a clot.)

Wraps a tight wrap around the puncture site that should stay in place for at least an hour

How to prepare for your blood test

Your doctor may ask you to fast or stop eating and drinking before the blood test.

Your doctor may also ask you to stop taking certain medications before the test, such as corticosteroids or antacids. These drugs increase the concentration of bicarbonate in the body.

Risks of a carbon dioxide blood test

There are slight risks associated with venipuncture and arterial blood tests. These include:

  • Excessive bleeding
  • Fainting.
  • Daze.
  • A hematoma is a lump of blood under the skin.
  • Infection at the puncture site.

After the blood is drawn, your doctor will make sure you feel fine and tell you how to care for the puncture site to reduce the chance of infection.

Test results

The total carbon dioxide (TCO2) blood test measures the total amount of carbon dioxide found inside the body.

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

The blood test often measures the pH of your blood along with carbon dioxide levels to further determine the cause of your symptoms.

Blood pH is a measure of acidity or alkalinity. Alkalosis is when your body fluids are too alkaline. On the other hand, acidosis is when your body fluids are too acidic.

Typically, blood is essential, with a pH measurement close to 7.4 in the body. The usual range of 7.35 to 7.45 is considered neutral.

A blood pH measurement below 7.35 is considered acidic. A substance is more alkaline when its blood pH measurement is more significant than 7.45.

My results were slightly abnormal – what should I do?

The ranges of typical values ​​can vary from laboratory to laboratory. A couple of points in either direction of the above content are often considered average results.

You will want to talk with your doctor or treatment team about what slightly abnormal results may mean to you.

Low bicarbonate (HCO3)

If there are lower bicarbonate levels than expected, this may indicate that some specific problems may be present and need to be addressed.

A low pH and low bicarbonate test result (less than 7.35) is called metabolic acidosis. Common causes are:

  • Renal failure .
  • Severe diarrhea
  • Lactic acidosis.
  • Seizures
  • Cancer.
  • Prolonged lack of oxygen due to severe anemia, heart failure, or shock.
  • Diabetic ketoacidosis (diabetic acidosis).

Low bicarbonate, high pH test result (greater than 7.45) is a respiratory alkalosis condition. Common causes are:

  • Hyperventilation
  • Fever.
  • Pain.
  • Anxiety.

The most common reason for low carbon dioxide levels in the body is recent or persistent diarrhea. It can also indicate the presence of the following problems.

  • Addison’s disease.
  • Ketoacidosis
  • Kidney disease
  • Metabolic acidosis.

High bicarbonate (HCO3)

If your total carbon dioxide (TCO2) blood test results are higher than usual, then the most common reason for this is due to recent vomiting.

A low pH, high bicarbonate test result (less than 7.35) is a condition called respiratory acidosis. Common causes are:

  • Pneumonia .
  • Chronic obstructive pulmonary disease (COPD).
  • Asthma.
  • Pulmonary fibrosis.
  • Exposure to toxic chemicals.
  • Medicines that suppress breathing, especially when combined with alcohol.
  • Tuberculosis.
  • Lung cancer.
  • Pulmonary hypertension.
  • Severe obesity

A test result for high bicarbonate and high pH (over 7.45) is metabolic alkalosis. Common causes are:

  • Chronic vomiting
  • Low potassium levels.

Certain respiratory disorders can also cause results higher than the normal range—hypoventilation, which involves slow breathing and decreased carbon dioxide removal.

The essential item to rule out with high results is Cushing’s syndrome, which means that a person’s body is producing too much cortisol or that there are medications that cause the production of too much cortisol.

Certain conditions change bicarbonate levels.

People who suffer from dementia or delirium, even in mild forms, may find that their bicarbonate levels are high or low.

In these circumstances, the total carbon dioxide (TCO2) blood test can be used as a first diagnostic effort to determine if there is anything abnormal within the body.

Additional tests may be ordered to follow up on high or low results.

This blood test is usually ordered even when there are no suspicions of health problems.

It is a tool used to confirm the presence of good health, just as it can be used to determine if there is a health situation that needs to be addressed.

Most people will have an average total carbon dioxide (TCO2) blood test result.

It may still be medically insignificant if an abnormal test result is received. Don’t ignore an abnormal test result, even if you don’t experience symptoms.

Talk to your doctor about what your total carbon dioxide (TCO2) blood test results mean, and that will allow you to begin a treatment regimen that will solve the problem and return your body to the balance it desires.

Long-term outlook

If your doctor finds a carbon dioxide imbalance that suggests acidosis or alkalosis, they will investigate the cause of this imbalance and treat it appropriately.

Because causes vary, treatment may include lifestyle changes, medications, and surgery.