When medical professionals refer to “carbon dioxide levels” in a blood test, they measure the amount of bicarbonate (HCO3-) in the blood. Bicarbonate is a natural byproduct of metabolism and plays a significant role in maintaining the body’s delicate acid-base (pH) balance. This balance is important for overall body function, and abnormal levels can signal various health conditions.
Understanding Blood Carbon Dioxide Levels
Measuring bicarbonate concentration in a blood test helps assess the body’s acid-base balance and electrolyte levels. Bicarbonate acts as a buffer, preventing the blood from becoming too acidic or too alkaline. It works alongside other electrolytes such as sodium, potassium, and chloride to maintain cellular stability and fluid balance throughout the body.
Normal blood bicarbonate levels for adults typically range from 22 to 32 millimoles per liter (mmol/L) or 23 to 29 milliequivalents per liter (mEq/L), though these ranges can vary slightly by laboratory. When a blood test shows “low” carbon dioxide, it indicates a bicarbonate level below this normal range, often pointing to metabolic acidosis, a condition with too much acid in the body’s fluids. The kidneys play a role in regulating bicarbonate by excreting or reabsorbing it to manage the body’s pH.
Key Reasons for Low Carbon Dioxide
A low bicarbonate level in the blood, indicating metabolic acidosis, can stem from various medical conditions and physiological processes where the body produces too much acid, cannot remove enough acid, or loses too much bicarbonate. Diabetic ketoacidosis (DKA) is a common cause, occurring when the body, often in type 1 diabetes, lacks enough insulin, leading to a buildup of acidic ketone bodies.
Lactic acidosis is another cause, resulting from lactic acid accumulation when the body breaks down carbohydrates for energy in low-oxygen conditions. Conditions such as cancer, excessive alcohol consumption, liver failure, heart failure, severe anemia, seizures, and sepsis can lead to lactic acidosis. Kidney disease, including chronic kidney disease (CKD) and acute kidney injury (AKI), can also cause low bicarbonate levels as impaired kidneys struggle to remove enough acid from the blood.
Severe diarrhea can lead to hyperchloremic acidosis, a type of metabolic acidosis caused by excessive loss of sodium bicarbonate. Certain medications, such as carbonic anhydrase inhibitors, can contribute to decreased bicarbonate levels. Poisoning from substances like aspirin, ethylene glycol (found in antifreeze), or methanol can also result in metabolic acidosis due to increased acid production or impaired kidney function. Severe dehydration, often from prolonged vomiting or diarrhea, can also disrupt the body’s acid balance and lead to low bicarbonate.
Symptoms Associated with Low Levels
Individuals with low blood bicarbonate levels, indicating metabolic acidosis, may experience a range of symptoms that often reflect the underlying cause or the body’s attempts to compensate for increased acidity. A noticeable symptom is rapid and deep breathing, sometimes called Kussmaul respirations, as the body tries to expel excess carbon dioxide to reduce acid. Initially, breathing may be rapid and shallow, progressing to deeper, more labored patterns as acidosis worsens.
Other common symptoms include nausea, vomiting, fatigue, and headaches. Confusion or lethargy may also occur, and in severe instances, altered consciousness or even shock can develop. Symptoms vary depending on the acidosis severity and its cause; milder cases or those that develop slowly might not show obvious symptoms.
How Low Carbon Dioxide is Addressed
Low carbon dioxide levels are typically diagnosed through blood tests, often as part of a basic or comprehensive metabolic panel, which measures bicarbonate along with other electrolytes. In severe cases, an arterial blood gas (ABG) test, which measures blood acidity directly from an artery, may be performed. These tests help determine if the body is properly balancing electrolytes and identify the presence of metabolic acidosis.
Addressing low bicarbonate primarily involves identifying and treating the underlying cause of metabolic acidosis. For example, diabetic ketoacidosis requires insulin therapy and fluid resuscitation, while lactic acidosis may necessitate addressing the source of infection or improving tissue perfusion. Supportive care, including fluid management, is often provided to help stabilize the patient. In specific and severe situations where pH levels are very low, medical professionals may administer intravenous sodium bicarbonate to help restore acid-base balance. This is carefully managed and not always recommended, particularly in cases like diabetic ketoacidosis.