Why is carbon dioxide (CO2) referred to as bicarbonate (bicarb) on a Comprehensive Metabolic Panel (CMP)?

From the Guidelines

CO2 is referred to as bicarb on a Comprehensive Metabolic Panel (CMP) because it measures the bicarbonate ion (HCO3-) in the blood, which is the primary form of CO2 in the bloodstream, accounting for 70-85% of carbon dioxide carriage 1.

Carbon Dioxide Physiology

The body's metabolism produces carbon dioxide, which is then cleared from the body through the lungs and kidneys. In the bloodstream, carbon dioxide is carried in three forms: bicarbonate, dissolved carbon dioxide, and bound to haemoglobin, with bicarbonate being the predominant form 1.

Bicarbonate Measurement

The bicarbonate measurement on a CMP is crucial for assessing acid-base balance in the body, as it represents the main buffer system that helps maintain blood pH within a normal range. This measurement quantifies the amount of bicarbonate in the blood, which is approximately proportional to the partial pressure of carbon dioxide in the blood within the physiological range 1.

Clinical Significance

Understanding bicarbonate levels helps clinicians evaluate kidney function, respiratory status, and metabolic conditions that might affect acid-base homeostasis. Normal bicarbonate values typically range from 22 to 29 mEq/L, with values outside this range potentially indicating metabolic acidosis or alkalosis. The importance of accurate bicarbonate measurement is highlighted in conditions such as chronic obstructive pulmonary disease (COPD), where excessive oxygen therapy can lead to carbon dioxide retention and acidosis 1.

Key Points

• CO2 is primarily carried in the blood as bicarbonate (70-85%) 1.
• Bicarbonate measurement on a CMP assesses acid-base balance and buffer system function.
• Normal bicarbonate values range from 22 to 29 mEq/L.
• Accurate bicarbonate measurement is crucial in evaluating and managing various metabolic and respiratory conditions.

From the Research

CO2 and Bicarbonate Relationship

• CO2 is not directly called bicarb, but rather, bicarbonate (HCO3-) is a related compound that helps regulate the body's acid-base balance.
• In the context of the Comprehensive Metabolic Panel (CMP), bicarbonate levels are measured to assess the body's acid-base status [ 2 ].

Bicarbonate Measurement on CMP

• The CMP measures bicarbonate levels in the blood, which can indicate metabolic alkalosis or acidosis [ 2 ].
• Bicarbonate is an important buffer that helps maintain the body's acid-base balance by neutralizing excess hydrogen ions [ 3 ].

CO2 and Bicarbonate Interrelationship

• CO2 is converted to bicarbonate (HCO3-) in the body through the action of the enzyme carbonic anhydrase [ 2 ].
• The relationship between CO2 and bicarbonate is crucial in maintaining the body's acid-base balance, and any imbalance can lead to metabolic alkalosis or acidosis [ 3 ].