A blood test showing low carbon dioxide (CO2) levels indicates an imbalance in the body’s acid-base regulation. In this context, CO2 primarily refers to the total CO2 in the blood, which is a measure of bicarbonate (HCO3-). Bicarbonate is a crucial electrolyte that acts as a buffer, helping to maintain the blood’s pH within a narrow, healthy range. When bicarbonate levels are low, it suggests the body has an excess of acid or has lost too much base.
Understanding Your CO2 Test Result
When a blood test reports a “CO2” level, it predominantly measures bicarbonate (HCO3-) in your blood plasma. Bicarbonate is a negatively charged ion that plays a central role in the body’s buffering system, which works to neutralize acids and keep blood pH stable. A normal range for total CO2 (bicarbonate) in adults is typically between 22 and 29 millimoles per liter (mmol/L).
A low CO2 reading generally signifies metabolic acidosis, a condition where there is too much acid in the body or a significant loss of bicarbonate. This is different from the gaseous carbon dioxide exhaled by the lungs, although the two are interconnected in the body’s acid-base balance. The kidneys and lungs work together to regulate these levels, with bicarbonate being the primary indicator of the metabolic component of this balance.
Common Causes of Low CO2
Several medical conditions and factors can lead to low bicarbonate levels, reflecting metabolic acidosis. One common cause is Diabetic Ketoacidosis (DKA), a serious complication of diabetes where insufficient insulin leads to the breakdown of fats for energy, producing acidic ketone bodies. This overwhelms the body’s buffering capacity, consuming bicarbonate and lowering CO2 levels.
Kidney disease is another frequent cause, as healthy kidneys are responsible for removing acids from the blood and regenerating bicarbonate. When kidney function declines, the kidneys cannot excrete enough acid, leading to an accumulation of acid and a drop in bicarbonate. Severe diarrhea can also cause low CO2 by leading to a significant loss of bicarbonate from the body.
Certain medications can impact bicarbonate levels. For example, carbonic anhydrase inhibitors, some diuretics, and metformin can contribute to metabolic acidosis. Aspirin overdose can also induce low CO2 levels. Furthermore, lactic acidosis, which occurs when the body produces too much lactic acid due to conditions like severe infection, shock, liver failure, or intense exercise, consumes bicarbonate and lowers CO2. Ingesting toxins such as methanol or ethylene glycol can also lead to severe metabolic acidosis and decreased bicarbonate.
Symptoms Associated with Low CO2
Symptoms associated with low CO2 levels, or metabolic acidosis, can vary depending on the severity and underlying cause. Individuals might experience rapid and deep breathing, sometimes referred to as Kussmaul respiration, as the body attempts to compensate by expelling more acidic carbon dioxide through the lungs. This breathing pattern is a compensatory mechanism to reduce acid in the blood.
Other general symptoms can include confusion, fatigue, and weakness. Nausea and vomiting are also possible. In more severe instances, altered consciousness may occur.
Next Steps After a Low CO2 Reading
Receiving a low CO2 reading on a blood test necessitates prompt consultation with a healthcare professional. This result indicates an acid-base imbalance that requires proper diagnosis and management. A medical provider will likely order additional diagnostic tests to determine the specific cause of the low bicarbonate.
These further tests might include an arterial blood gas (ABG) analysis, which provides a detailed picture of blood pH, oxygen, and carbon dioxide levels. An electrolyte panel or kidney function tests may also be performed to assess overall metabolic health and kidney performance. Management will focus on treating the underlying condition responsible for the low CO2, rather than just attempting to normalize the bicarbonate level directly. This targeted approach is essential for addressing the root cause of the acid-base disturbance.