What Is a Bicarbonate Blood Test?

Medically Reviewed by Nayana Ambardekar, MD on March 31, 2024
2 min read

Bicarbonate is a form of carbon dioxide (CO2), a gas waste left when your body burns food for energy. Bicarbonate belongs to a group of electrolytes, which help keep your body hydrated and make sure your blood has the right amount of acidity. Too much or too little bicarbonate can be a sign of a number of conditions, including diarrhea, liver failure, kidney disease, and anorexia.

A bicarbonate test measures how much carbon dioxide is in your blood.

It’s usually part of a larger electrolyte test that tells your doctor how much sodium, potassium, and chloride is in your body. They may do this test as part of a regular checkup, or to try to find out why you don’t feel well.

Your doctor might check the CO2 levels in your blood if you have:

If you’re being treated for kidney, liver, lung, or digestive conditions, your doctor might check your bicarbonate levels regularly to see if your therapy or medication is working.

A doctor or nurse will take a sample of your blood from your arm with a needle. Let your doctor know if you take any medications or supplements, because they can affect the results. So can eating grapefruits, tangerines, and other fruits high in acid.

The test uses only the fluid in your blood, not the blood cells or the platelets that help your blood clot. A lab technician will add acid to the liquid to unlock carbon dioxide from the bicarbonate. The amount of bicarbonate is measured by how fast the sample’s acidity changes.

Your test measures how many millimoles of carbon dioxide is in a liter, or about a quart, of fluid (mmol/L). A normal result is between 23 and 29 mmol/L for adults but may vary by lab.

A low CO2 level can be a sign of several conditions, including:

  • Kidney disease
  • Diabetic ketoacidosis, which happens when your body’s blood acid level goes up because it doesn’t have enough insulin to digest sugars
  • Metabolic acidosis, which means your body makes too much acid
  • Addison’s disease, a rare condition that affects the hormone-producing adrenal glands
  • Ethylene glycol poisoning. This sweet-tasting chemical is in antifreeze, detergents, paints, and other household products.
  • Aspirin overdose

High CO2 in blood may point to: