What is Bicarbonate?
Bicarbonate is an electrolyte, a negatively charged ion that is used by the body to help maintain the body’s acid-base (pH) balance. It also works with the other electrolytes (sodium, potassium, and chloride) to maintain electrical neutrality at the cellular level. This test measures the total amount of carbon dioxide (CO2) in the blood, which occurs mostly in the form of bicarbonate (HCO3–). CO2 is mainly a by-product of various metabolic processes.
Measuring bicarbonate as part of an electrolyte or metabolic panel may help diagnose an electrolyte imbalance or acidosis or alkalosis. Acidosis and alkalosis describe the abnormal conditions that result from an imbalance in the pH of the blood caused by an excess of acid or alkali (base). This imbalance is typically caused by some underlying condition or disease.
The lungs and kidneys are the major organs involved in regulating blood pH through the removal of excess bicarbonate.
- The lungs flush acid out of the body by exhaling CO2. Raising and lowering the respiratory rate alters the amount of CO2 that is breathed out, and this can affect blood pH within minutes.
- The kidneys eliminate acids in the urine and they regulate the concentration of bicarbonate (HCO3–, a base) in blood. Acid-base changes due to increases or decreases in HCO3– concentration occur more slowly than changes in CO2, taking hours or days.
Any disease or condition that affects the lungs, kidneys, metabolism, or breathing has the potential to cause acidosis or alkalosis.
The bicarbonate test gives a rough estimate of your acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood (blood gases) may be done if more information is needed. Bicarbonate is typically measured along with sodium, potassium, and possibly chloride in an electrolyte panel as it is the balance of these molecules that gives the most information.
How is the test used?
The bicarbonate (or total CO2) test is usually taken along with sodium, potassium, and chloride as part of an electrolyte panel, which is included in a basic metabolic panel (BMP) and a comprehensive metabolic panel (CMP). A calculated bicarbonate level might also be reported as part of a blood gas panel.
The electrolyte panel may be used to help detect, evaluate, and monitor electrolyte imbalances and/or acid-base (pH) imbalances (acidosis or alkalosis). The tests may be used as part of a routine health exam or to help evaluate and monitor a variety of chronic or acute illnesses, such as:
- Kidney disease
- Liver disease
- Lung disorders
- High blood pressure (hypertension)
When acidosis or alkalosis is identified, bicarbonate tests and blood gases may be ordered to evaluate the severity of the pH imbalance. These tests help determine whether it is primarily respiratory (due to an imbalance between the amount of oxygen coming in and CO2 being released) or metabolic (due to imbalance in the amount of acid produced by the body or ability of the kidneys to remove acid from the body). They also help monitor treatment until acid-base balance is restored.
