Bicarbonate (HCO₃⁻) in Serum/Plasma

The bicarbonate (CO2) test measures the amount of bicarbonate, a form of carbon dioxide, in your blood. Bicarbonate helps keep your body's acid-base (pH) balance steady and reflects how well your kidneys and lungs are working together to maintain healthy blood chemistry.

Bicarbonate is a critical buffer in your blood, helping to counteract acid produced by normal metabolic processes. Your body tightly regulates bicarbonate levels to keep your blood pH within a narrow range (typically slightly alkaline). This test checks the concentration of bicarbonate in your serum or plasma, which can indicate whether your body is producing too much or too little of it.

Your doctor may order this test as part of a basic metabolic panel, comprehensive metabolic panel, or electrolyte panel to check for kidney problems, breathing disorders, or metabolic conditions, and to monitor treatment for issues that affect acid-base balance, such as dehydration, prolonged vomiting, or diabetes.

Doctors may order a bicarbonate test to diagnose or monitor conditions affecting acid-base balance, such as metabolic acidosis or alkalosis. It’s also used in cases of kidney disease, diabetes, respiratory disorders, or after certain medications or treatments.

Abnormal bicarbonate results can suggest acidosis (too much acid in the body) or alkalosis (too little acid). High levels may be linked to lung disease, prolonged vomiting, or certain kidney conditions, while low levels can occur with kidney disease, severe diarrhea, or uncontrolled diabetes. Your provider will interpret results along with other tests.

Low bicarbonate levels (acidosis) may suggest conditions like kidney failure, severe dehydration, or overuse of certain medications (e.g., diuretics). High bicarbonate levels (alkalosis) could indicate conditions like vomiting, excessive antacid use, or metabolic alkalosis from prolonged vomiting or diarrhea.

The test is done with a simple blood draw, usually from a vein in your arm. A healthcare professional cleans the site, inserts a small needle, and collects a sample into a tube. The procedure takes only a few minutes, may cause a brief sting, and most people can return to normal activities right away.

A blood sample is drawn from a vein in your arm, usually in a clinic or lab. The blood is processed to separate serum or plasma, and the bicarbonate concentration is measured using a specialized lab method (often automated chemistry or ion-selective electrode techniques).