Carbon Dioxide (CO₂) in Blood: Levels and Health Impact

What Is Carbon Dioxide?

Carbon dioxide (CO₂) is a gas that plays a crucial role in maintaining the body's acid-base balance.

It is a byproduct of metabolism, produced when cells break down nutrients for energy. The lungs remove excess CO₂ through exhalation, while the kidneys help regulate its levels in the blood.

Doctors measure CO₂ levels to assess respiratory function and acid-base balance. This biomarker is essential for diagnosing conditions related to lung function, kidney health, and metabolic imbalances.

When Is Carbon Dioxide Testing Recommended?

A carbon dioxide test is usually ordered when a doctor suspects an acid-base imbalance or a breathing disorder. It helps diagnose and monitor several conditions.

Common reasons for testing include:

• Respiratory issues: To assess breathing problems caused by lung diseases like asthma, chronic obstructive pulmonary disease (COPD), or pneumonia.
• Metabolic imbalances: To evaluate acid-base disorders, including metabolic acidosis and alkalosis.
• Kidney function assessment: To check if the kidneys are properly regulating acid-base balance.
• Critical illness monitoring: To ensure proper ventilation in patients on artificial respiration.
• Unexplained symptoms: If a person experiences confusion, dizziness, fatigue, or rapid breathing, a CO₂ test can help determine if an imbalance is present.

How Is Carbon Dioxide Testing Conducted?

Carbon dioxide levels are measured through a blood test, which can be done using:

• Arterial blood sample: Taken from an artery, usually the wrist, to get an accurate reading of blood gases, including CO₂.
• Venous blood sample: Collected from a vein, commonly as part of a metabolic panel.

Types of Tests That Include CO₂ Measurement

• Metabolic Panel: Includes CO₂ measurement along with other essential blood markers to assess kidney function, electrolyte balance, and acid-base status.
• Blood Gas Test (ABG Test): Provides a detailed analysis of oxygen, carbon dioxide, and pH levels in arterial blood.

Preparations for the Test

• Fasting: Not usually required, but some doctors may recommend avoiding food or drinks for a few hours.
• Medication adjustments: Certain medications can affect CO₂ levels, so inform your doctor about any treatments you are on.
• Avoid strenuous exercise: Physical activity before the test can alter carbon dioxide levels temporarily.

What Are the Normal Carbon Dioxide Levels?

CO₂ levels in the blood are measured in milliequivalents per liter (mEq/L) or millimoles per liter (mmol/L). The normal range for adults is:

• 23 to 29 mEq/L
• 23 to 29 mmol/L

Note: The units of measurement and the normal ranges can differ depending on the laboratory and the specific methods used.

What Do Abnormal Levels Mean?

Abnormal CO₂ levels may indicate an issue with breathing, kidney function, or metabolic processes. Both high and low levels can have serious health implications.

High Carbon Dioxide Levels

Elevated CO₂ in the blood, also known as respiratory acidosis, can occur when the lungs fail to remove enough carbon dioxide.

Common Causes of High CO₂ Levels:

• Lung diseases: Conditions like COPD, asthma, or pneumonia reduce the ability to expel CO₂ efficiently.
• Impaired breathing: Severe obesity, muscle weakness, or nervous system disorders can affect respiration.
• Chronic obstructive pulmonary disease (COPD): People with COPD often retain too much CO₂ due to poor lung function.
• Artificial ventilation issues: Incorrect ventilator settings may cause CO₂ retention in critical care patients.
• Metabolic imbalances: Conditions that cause excessive acid buildup in the body can increase CO₂ levels.

• Improve lung function: Practice breathing exercises to enhance oxygen exchange.
• Maintain a healthy weight: Excess weight can make breathing harder, worsening CO₂ retention.
• Avoid smoking: Tobacco damages lung tissues, reducing CO₂ elimination.
• Monitor oxygen therapy: If using supplemental oxygen, follow your doctor’s guidelines to prevent CO₂ buildup.
• Consult a healthcare provider: If CO₂ levels are consistently high, a specialist may need to adjust treatment.

Low Carbon Dioxide Levels

Decreased CO₂ levels, known as respiratory alkalosis, usually occur when the body loses too much carbon dioxide due to excessive breathing.

Common Causes of Low CO₂ Levels:

• Hyperventilation: Rapid breathing due to anxiety, pain, or stress can cause excessive CO₂ loss.
• Severe infections: Conditions like sepsis can lead to metabolic imbalances that lower CO₂ levels.
• Kidney disorders: Impaired kidney function can affect bicarbonate levels, which influences CO₂ balance.
• Salicylate poisoning: Certain substances can cause excessive acid buildup, leading to a drop in CO₂.
• Severe trauma: Injuries to the brain or lungs can affect breathing patterns, altering CO₂ levels.

• Practice controlled breathing: If hyperventilating, slow your breathing by inhaling through your nose and exhaling slowly.
• Stay hydrated: Proper fluid intake helps maintain electrolyte and acid-base balance.
• Manage underlying conditions: Work with a doctor to treat infections, kidney disorders, or metabolic imbalances.
• Reduce stress: Relaxation techniques like meditation or yoga can help control breathing.
• Seek medical advice: If symptoms like dizziness, confusion, or rapid breathing persist, consult a healthcare provider.

Which Specialist Should You Consult?

The right specialist depends on the cause of abnormal CO₂ levels. If your test results are outside the normal range, a doctor may refer you to:

• Pulmonologist: For lung-related conditions like asthma, COPD, or respiratory failure.
• Nephrologist: If kidney dysfunction is affecting CO₂ balance.
• Critical care specialist: For patients requiring mechanical ventilation or intensive monitoring.
• Endocrinologist: If metabolic imbalances or hormonal disorders are involved.
• General practitioner: To evaluate overall health and determine if further testing is needed.