About the Test
Purpose of the test
Measuring HCO3- as part of an electrolyte or metabolic panel may help diagnose an electrolyte imbalance. It can also diagnose acidosis or alkalosis, the abnormal conditions that result from an imbalance in the pH of the blood caused by an excess of acid or alkali (base). Some underlying condition or disease typically causes this imbalance.
What does the test measure?
Bicarbonate-carbonic acid buffer is one of the most important buffer systems in maintaining normal blood and body fluid acid-base balance (pH). HCO3- is an electrolyte, a negatively charged ion used by the body to help maintain the acid-base balance in the body. It also works with other electrolytes (sodium, potassium, and chloride) to maintain electrical neutrality at the cellular level.
This test measures the total amount of CO2 in the blood, which occurs mostly in the form of HCO3– (90% to 95%). CO2 is mainly a by-product of various metabolic processes.
The HCO3– test gives a health care practitioner a rough estimate of your acid-base balance. This is usually sufficient, but measurements of gasses dissolved in the blood (blood gases) may be done if more information is needed.
HCO3– is typically measured along with sodium, potassium, and possibly chloride in an electrolyte panel as the balance of these molecules gives the health care practitioner the most information.
When should I get this test?
HCO3– testing may be ordered when you have a routine health checkup.
This testing may also be ordered when acidosis or alkalosis is suspected or when you have an acute condition with symptoms such as:
- Prolonged vomiting and/or diarrhea
- Weakness, fatigue
- Difficulty breathing (respiratory distress)
Electrolytes may be ordered at regular intervals when you have a disease or condition or are taking a medication that can cause an electrolyte imbalance.
Finding a Bicarbonate Test
How can I get a Total CO2 test?
A total CO2 test is typically included in an electrolyte panel test. Usually, it is ordered by a health care provider and taken at a lab, hospital or medical facility.
Can I take the test at home?
An HCO3– test is not currently offered as an at-home test.
How much does the test cost?
As part of an electrolyte panel test, testing your HCO3– level is often considered routine blood work. As such, the cost is typically affordable, under $50. In addition, if you have health insurance, you may be fully or partially covered.
Taking a Bicarbonate Test
A HCO3– test is part of a blood test taken from a vein in the arm.
Before the test
There is usually no special preparation required to test your HCO3– levels. You shouldn’t have to fast or do anything else.
During the test
An electrolyte panel, which includes an HCO3– test, is a simple blood draw. A health care provider will find a viable vein in your arm and prepare the area with an alcohol pad. They will also tie an elastic band around your upper arm to help the vein become more prominent. A needle will be inserted into the vein. You may feel a slight pinch.
The blood will be collected in a tube. When enough of a sample has been taken, the elastic will be removed, and the needle will be taken out. The area will be bandaged and you will apply a bit of pressure to minimize any bleeding.
After the test
You likely won’t experience any side effects after the blood test. There may be some minor bruising on your arm, but otherwise, you can resume your normal activities.
Bicarbonate Test Results
Receiving test results
Test results for an electrolyte panel usually take about one to two business days. Your health care provider or lab will contact you, or if you have a patient portal, you may be able to see your results online or via an app.
Interpreting test results
HCO3– levels are typically interpreted along with results from other tests done at the same time, such as the other electrolytes.
In general, adult HCO3– levels should be between 23 to 29 milliequivalents per liter (mEq/L).
An HCO3– level higher or lower than normal may mean that the body is having trouble maintaining its acid-base balance, either by failing to remove CO2 through the lungs or the kidneys or perhaps because of an electrolyte imbalance, particularly a deficiency of potassium. Both of these imbalances may be due to a wide range of conditions.
Examples of conditions that can cause a low HCO3– level include:
- Addison’s disease
- Chronic diarrhea
- Diabetic ketoacidosis
- Metabolic acidosis
- Respiratory alkalosis, which can be caused by hyperventilation
- Kidney disease
- Ethylene glycol or methanol poisoning
- Salicylate (aspirin) overdose
Examples of conditions that can cause a high HCO3– level include:
- Severe, prolonged vomiting and/or diarrhea
- Lung diseases, including chronic obstructive pulmonary disease (COPD)
- Cushing’s syndrome
- Conn’s syndrome
- Metabolic alkalosis
- Drugs such as diuretics
Once you receive your HCO3– test result, it can be helpful to ask your doctor some questions, which may include:
- Are my CO2 levels within the normal range, and if not, what does that mean?
- Will any follow-up testing be needed?
- If an electrolyte imbalance is evident, what are the next steps?
A.D.A.M. Medical Encyclopedia. Acidosis. Updated November 6, 2021. Accessed on January 23, 2023. https://medlineplus.gov/ency/article/001181.htm
A.D.A.M. Medical Encyclopedia. Alkalosis. Updated November 6, 2021. Accessed on January 23, 2023. https://medlineplus.gov/ency/article/001183.htm
A.D.A.M. Medical Encyclopedia. Metabolic Acidosis. Updated November 6, 2021. Accessed on January 23, 2023. https://medlineplus.gov/ency/article/000335.htm
American Board of Internal Medicine. ABIM Laboratory Test Reference Ranges. Updated January 2022. Accessed January 23, 2023. https://www.abim.org/Media/bfijryql/laboratory-reference-ranges.pdf
American Kidney Fund. Metabolic Acidosis. Updated November 11, 2021. Accessed January 23, 2023. https://www.kidneyfund.org/living-kidney-disease/health-problems-caused-kidney-disease/metabolic-acidosis-symptoms-complications-treatment
Merck Manual. Metabolic Acidosis. Updated September 2022. Accessed January 23, 2023. https://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/acid-base-regulation-and-disorders/metabolic-acidosis