Carbon Dioxide Lab Test
|See Also||Lab Tests|
The carbon dioxide lab test, also known as total CO2 or bicarbonate, is a measure of bicarbonate in the blood. This is because the majority of CO2 (about 75%) produced during cellular respiration, is carried in the blood in the form of bicarbonate ions. 20% of carbon dioxide remains combined with hemoglobin and other plasma proteins, while the remaining 5% is found in solution as dissolved Co2. The dissolved CO2 that is formed in the lungs contributes little to the CO2 value.,
- CO2, as bicarbonate, contributes to acid-base balancing. A carbon dioxide lab test is typically part of an electrolyte panel to identify or monitor an electrolyte imbalance or acid-base (pH) imbalance.
- Metabolic acids, such as hydrochloric acid and lactic acid, are neutralized by bicarbonate.
- Bicarbonate acts as one of the reserve alkaline elements in the blood.
- No fasting is required.
- Factors which can cause increased levels
- Drugs: aldosterone, barbiturates, bicarbonates, ethacrynic acid, hydrocortisone, loop diuretics, mercurial diuretics, and steroids
- Factors which can cause decreased levels
- underfilling the tube with blood allows CO2 to escape from the serum specimen
- Drugs: methicillin, nitrofurantoin (Furadantin), paraldehyde, phenformin, tetracycline, thiazide diuretics, and triamterene.
Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. 
|Standard U.S. Units||Standard International Units|
|Conventional Laboratory Range||23-32 mEq/L||23-32 mmol/L|
|Optimal Range||25-30 mEq/L||25-30 mmol/L|
|Alarm Ranges||< 18 or > 38 mEq/L||< 18 or > 38 mmol/L|
High levels indicate:
- Metabolic alkalosis
- Respiratory acidosis
- Severe vomiting
- Lung diseases, incluidng COPD
- Adrenal hyperfunction
- Other conditions: fever, hot baths, vomiting (loss of HCL), emphysema (respiratory distress), aldosteronism
Low levels indicate:
- Chronic diarrhea
- Metabolic acidosis
- Diabetic ketoacidosis
- Respiratory alkalosis
- Kidney Disease
- Addison's Disease
- Thiamine (Vitamin B1) deficiency
- Drug causes: Salicylate excess (aspirin), Diuretics (chlorothiazide class)
- Other conditions: dehydration, sleep apnea or shallow breathing, highly refined diet
- Pagana Kathleen D, Pagana Timothy J (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
- Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain.