Carbon dioxide (CO2) is a natural byproduct generated as cells convert food into energy. A blood test measures CO2 levels, often as part of a metabolic panel, providing insight into the body’s chemical balance. A low CO2 level can signal an underlying imbalance.
Carbon Dioxide’s Role in the Body
Cells continuously produce carbon dioxide (CO2) as a metabolic waste product, transported to the lungs for exhalation. CO2 also helps maintain the body’s pH balance, the precise balance between acids and bases in the blood. This balance is important for normal cellular function, as even slight deviations can affect many organs.
The body uses a buffer system, involving CO2, water, and bicarbonate ions, to keep blood pH within a narrow range, typically between 7.35 and 7.45. The lungs regulate CO2 levels by adjusting breathing speed and depth, while the kidneys help manage bicarbonate levels. In a blood test, CO2 is usually measured as “total CO2” or bicarbonate, representing most of the CO2 in the blood. Normal total CO2 levels in adults typically range from 23 to 30 mEq/L.
Reasons for Low Levels
Low blood CO2 levels often point to metabolic acidosis or respiratory alkalosis. Metabolic acidosis occurs with excess acid or significant bicarbonate loss, a base that helps neutralize acids. The body attempts to compensate by increasing breathing to expel more CO2, which is mildly acidic.
Metabolic acidosis can result from conditions like diabetic ketoacidosis (DKA), where acidic ketone bodies build up due to uncontrolled diabetes. Kidney failure can also cause this imbalance, as kidneys may not remove enough acid from the body. Other causes include severe dehydration, aspirin overdose, or significant bicarbonate loss from severe diarrhea. Lactic acidosis, resulting from a buildup of lactic acid due to conditions like severe infection, organ failure, or prolonged lack of oxygen, also contributes.
Respiratory alkalosis develops when a person breathes too rapidly or deeply, a process known as hyperventilation. This excessive breathing expels too much CO2, leading to lower blood levels and an increase in blood pH, making the blood more alkaline. Common causes include anxiety or panic attacks.
Other factors inducing respiratory alkalosis include pain, fever, or exposure to high altitudes, where the body breathes faster to compensate for lower oxygen levels. Certain lung diseases, such as asthma exacerbation, or neurological conditions that affect the brain’s respiratory control center can also lead to low CO2. Additionally, some medications, like salicylates (aspirin), can stimulate the respiratory center.
Recognizing Symptoms and Potential Concerns
Symptoms associated with low blood CO2 levels vary widely, depending on the underlying cause and its severity. For metabolic acidosis, the body attempts to reduce acidity by increasing breathing, which can manifest as rapid, deep (Kussmaul) breaths. Other symptoms may include nausea, vomiting, abdominal pain, and fatigue. As the condition progresses, confusion or lethargy can occur.
In respiratory alkalosis, individuals might experience lightheadedness, dizziness, or numbness and tingling sensations in the hands and feet. Shortness of breath and a rapid heartbeat are common. A low CO2 level is a concern because it indicates an acid-base imbalance, which can affect organ function if left unaddressed.
What Happens Next
If a blood test reveals low CO2 levels, a doctor will conduct a thorough evaluation, considering the patient’s symptoms and medical history. This initial assessment helps understand the potential reasons behind the abnormal result. Additional tests are often ordered to pinpoint the exact cause.
Further tests might include an arterial blood gas (ABG) test, which provides a more detailed assessment of oxygen, CO2, and pH levels from an artery. An electrolyte panel (measuring sodium, potassium, and chloride) or kidney function tests may also be performed.
Treatment focuses on addressing the underlying condition that caused the low CO2. For instance, diabetic ketoacidosis may require insulin therapy and fluid replacement. If hyperventilation is the cause, techniques to slow breathing or addressing anxiety may be employed. Consulting a healthcare professional is important for proper diagnosis and management, as self-diagnosis or self-treatment can be harmful.