CO2
Also known as: Bicarbonate, HCO3
What Does CO2 Measure?
The CO2 test, also known as bicarbonate (HCO3) or total carbon dioxide, measures the amount of carbon dioxide in your blood, primarily in the form of bicarbonate. Bicarbonate is a chemical that acts as a buffer, helping to maintain the proper acid-base balance (pH) in your body. This test is almost always included in a basic or comprehensive metabolic panel (BMP/CMP) and reflects how well your kidneys and lungs are working together to regulate the body's chemistry.
Why Does CO2 Matter?
Maintaining the right level of CO2 in the blood is essential for keeping the body's pH within a narrow, healthy range. When CO2 levels are too high or too low, it can signal problems with kidney function, lung disease, metabolic disorders, or electrolyte imbalances. Doctors use this test to detect conditions like metabolic acidosis (too much acid) or metabolic alkalosis (too little acid), monitor chronic kidney disease, evaluate breathing disorders, and guide treatment for patients with diabetes or severe dehydration. It is a critical component of understanding overall metabolic health.
Normal Ranges
Males
23–29 mEq/L (millequivalents per liter)
Females
23–29 mEq/L (millequivalents per liter)
Children
20–28 mEq/L (varies slightly by age; infants may run slightly lower)
Causes of High Levels
- Metabolic alkalosis – often caused by vomiting, which leads to loss of stomach acid
- Chronic obstructive pulmonary disease (COPD) or respiratory failure – lungs retain excess CO2
- Diuretic medication use – certain diuretics cause the kidneys to retain bicarbonate
- Hyperaldosteronism – excess aldosterone hormone causes the kidneys to retain bicarbonate
- Severe dehydration or volume contraction – concentrates bicarbonate in the blood
- Cushing's syndrome – excess cortisol can indirectly raise bicarbonate levels
Causes of Low Levels
- Metabolic acidosis – common in uncontrolled diabetes (diabetic ketoacidosis) or kidney failure
- Chronic kidney disease – kidneys lose the ability to retain and produce bicarbonate
- Diarrhea – significant loss of bicarbonate through the gastrointestinal tract
How to Improve Your CO2
Diet
- Eat an alkaline-promoting diet rich in fruits and vegetables (especially leafy greens, bananas, and avocados) to help buffer excess acid
- Reduce intake of high-acid foods such as processed meats, refined sugars, and excessive animal proteins that increase the body's acid load
- Stay well hydrated with water throughout the day to support kidney function and proper bicarbonate regulation
- Limit alcohol consumption, which can disrupt acid-base balance and impair kidney function
- Include potassium-rich foods like sweet potatoes, beans, and oranges to support electrolyte and pH balance
Supplements
- Sodium bicarbonate (baking soda) – sometimes prescribed by physicians at 650–1300 mg per day for patients with chronic kidney disease and low CO2; do not self-supplement without medical guidance
- Potassium citrate – 10–20 mEq per day may help manage metabolic acidosis in kidney disease patients under medical supervision
- Magnesium glycinate – 200–400 mg daily supports kidney function and electrolyte balance, which indirectly affects CO2 levels
- Vitamin D3 – 1000–2000 IU daily to support kidney health, as deficiency is linked to impaired bicarbonate regulation
Related Biomarkers
Frequently Asked Questions
What does it mean if my CO2 is low on a blood test?
A low CO2 (bicarbonate) level typically indicates that your blood is too acidic, a condition called metabolic acidosis. Common causes include uncontrolled diabetes (diabetic ketoacidosis), kidney disease, severe diarrhea, or the buildup of lactic acid. A single mildly low result may not be alarming, but persistently low levels require investigation by your doctor to find and treat the underlying cause.
Is the CO2 on a blood panel the same as what my lungs breathe out?
Not exactly. The CO2 measured in a standard blood panel (BMP or CMP) reflects the total carbon dioxide in your blood, mostly in the form of bicarbonate (HCO3), which is a chemical buffer produced primarily by the kidneys. The CO2 you breathe out from your lungs is gaseous carbon dioxide. While they are related — both reflect your body's acid-base balance — the blood test measures the chemical form, not the gas directly.
What is a dangerously low or high CO2 level?
A CO2 level below 15 mEq/L is considered significantly low and may indicate severe metabolic acidosis requiring urgent medical attention. A level above 35 mEq/L is considered markedly elevated and can signal severe metabolic alkalosis or significant respiratory failure. Both extremes can be life-threatening and require immediate evaluation. Levels between 20–22 mEq/L (low-normal) or 30–32 mEq/L (high-normal) may warrant monitoring but are less immediately concerning.
Can dehydration affect my CO2 level?
Yes. Severe dehydration can concentrate bicarbonate in the blood, potentially causing a falsely elevated CO2 reading. On the other hand, dehydration that leads to poor kidney perfusion can impair bicarbonate regulation over time, potentially lowering CO2. Staying well-hydrated is important for maintaining normal electrolyte and acid-base balance.