Bicarbonate is a naturally occurring substance in your blood that acts as a buffer, preventing your body from becoming too acidic or too alkaline. When you see “bicarbonate,” “HCO3,” or “total CO2” on your blood test results, they’re all measuring essentially the same thing: how well your body is maintaining its acid-base balance. A normal bicarbonate level falls between 23 and 28 mEq/L.
Why It Shows Up as “CO2” on Your Results
This is one of the most confusing parts of reading your lab work. Most of the carbon dioxide in your blood actually exists in the form of bicarbonate, not as a gas. So when the lab measures your total CO2, it’s really measuring your bicarbonate level. You might see it labeled as “TCO2,” “total CO2,” or “CO2” on a basic metabolic panel. Don’t confuse this with a blood gas test, which measures dissolved carbon dioxide gas directly. On a standard blood panel, CO2 means bicarbonate.
What Bicarbonate Does in Your Body
Your blood needs to stay within a very narrow pH range to function properly. Bicarbonate is one of the main tools your body uses to keep that balance. It works like a chemical sponge, soaking up excess acid so your blood doesn’t become dangerously acidic.
Two organs share the job of maintaining this balance. Your lungs remove acid by breathing out carbon dioxide. Your kidneys handle the finer adjustments: they reabsorb nearly all the bicarbonate that gets filtered through them (about 70 to 80% in the first section of the kidney’s filtering tubes alone) and can also generate brand-new bicarbonate when your body needs more. The kidneys create this new bicarbonate partly by breaking down an amino acid called glutamine, a process that produces two bicarbonate molecules for every glutamine molecule used. This system gives your body a way to replenish bicarbonate that gets consumed neutralizing acids from food, exercise, and normal metabolism.
What Low Bicarbonate Means
A bicarbonate level below 23 mEq/L suggests your blood is more acidic than it should be, a condition called metabolic acidosis. This happens when your body is either producing too much acid or can’t get rid of acid fast enough.
Chronic kidney disease is one of the most common causes. As kidney function declines, the kidneys lose their ability to excrete the daily acid load your body produces. They can’t generate enough of a compound called ammonia to neutralize that acid, so bicarbonate gets used up faster than it can be replaced. Over time, this leads to real consequences: bone weakening, muscle loss, and faster progression of the kidney disease itself.
Other conditions that can lower bicarbonate include uncontrolled diabetes (where the body produces acidic compounds called ketones), severe diarrhea (which flushes bicarbonate out of the body), and certain medications. A study published in Kidney360 found that metformin, a common diabetes drug, was associated with bicarbonate levels about 1.2 mEq/L lower than in people not taking it. A nerve pain medication called gabapentin had a similar effect, lowering levels by about 1.0 mEq/L. When both were taken together, the combined drop was 1.8 mEq/L, enough to potentially push someone with already borderline levels into the abnormal range.
What High Bicarbonate Means
A level at or above 28 mEq/L points toward metabolic alkalosis, meaning your blood is too alkaline. The most straightforward cause is losing too much acid, which often happens through prolonged vomiting or severe dehydration. When you’re dehydrated, you lose key electrolytes, and the concentration of bicarbonate in your blood rises relative to everything else.
Other causes include low potassium levels, low chloride levels, overproduction of the adrenal hormone aldosterone, and heart, kidney, or liver failure. Some genetic conditions can also cause the kidneys to release too many electrolytes, tipping the balance toward alkalosis.
How the Test Is Done
Bicarbonate is typically measured as part of a basic metabolic panel (BMP), a routine group of blood tests that checks several chemicals in your blood at once. You’ll usually need to fast for 8 to 12 hours beforehand, drinking only plain water. During the fast, you should also avoid chewing gum, smoking, and exercise, as these can affect results.
The test itself is a simple blood draw. Results usually come back quickly, often the same day or the next.
How to Read Your Results
The generally accepted normal range is 23 to 28 mEq/L (sometimes written as mmol/L, which is the same number). Your lab report may show a slightly different reference range, since labs sometimes use their own cutoffs. Compare your result to the range printed on your specific report.
A single abnormal reading doesn’t necessarily mean something is wrong. Dehydration, recent vomiting, intense exercise, or even the medications you take can temporarily shift your bicarbonate level. If your result is outside the normal range, your doctor will typically look at it alongside other values on the same panel, like sodium, potassium, and chloride, to get the full picture. A pattern of consistently low or high bicarbonate across multiple tests is more meaningful than a single off result.
For people with chronic kidney disease, bicarbonate is tracked closely over time. A downward trend signals worsening acid buildup and may prompt changes in treatment to slow further kidney damage and protect bone and muscle health.