Blood Health

Bicarbonate (HCO3), Serum

Optimal Result: 22 - 29 mmol/L.

Bicarbonate is an electrolyte, a negatively charged ion that is used by the body to help maintain the body’s acid-base (pH) balance. It also works with the other electrolytes (sodium, potassium, and chloride) to maintain electrical neutrality at the cellular level. This test measures the total amount of carbon dioxide (CO2) in the blood, which occurs mostly in the form of bicarbonate (HCO3–). The CO2 is mainly a by-product of various metabolic processes.

Measuring bicarbonate as part of an electrolyte or metabolic panel may help diagnose an electrolyte imbalance or acidosis or alkalosis. Acidosis and alkalosis describe the abnormal conditions that result from an imbalance in the pH of the blood caused by an excess of acid or alkali (base). This imbalance is typically caused by some underlying condition or disease.

The lungs and kidneys are the major organs involved in regulating blood pH through the removal of excess bicarbonate.

The lungs flush acid out of the body by exhaling CO2. Raising and lowering the respiratory rate alters the amount of CO2 that is breathed out, and this can affect blood pH within minutes.

The kidneys eliminate acids in the urine and they regulate the concentration of bicarbonate (HCO3–, a base) in blood. Acid-base changes due to increases or decreases in HCO3– concentration occur more slowly than changes in CO2, taking hours or days.

Any disease or condition that affects the lungs, kidneys, metabolism, or breathing has the potential to cause acidosis or alkalosis.

The bicarbonate test gives a healthcare practitioner a rough estimate of your acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood (blood gases) may be done if more information is needed. Bicarbonate is typically measured along with sodium, potassium, and possibly chloride in an electrolyte panel as it is the balance of these molecules that gives the healthcare practitioner the most information.

Bicarbonate Reference Ranges:

The reference ranges provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your healthcare provider.

AGE CONVENTIONAL UNITS2 SI UNITS3
0-18 years Not available due to wide variability. See child’s lab report for reference range.
Adult 23-29 mEq/L 23-29 mmol/L
>60 years 23-31 mEq/L 23-31 mmol/L
>90 years 20-29 mEq/L 20-29 mmol/L

What does it mean if your Bicarbonate (HCO3), Serum result is too low?

A bicarbonate level that is higher or lower than normal may mean that the body is having trouble maintaining its acid-base balance, either by failing to remove carbon dioxide 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 bicarbonate level include:

- Addison disease

- Chronic diarrhea

- Diabetic ketoacidosis

- Metabolic acidosis

- Respiratory alkalosis, which can be caused by hyperventilation

- Shock

- Kidney disease

- Ethylene glycol or methanol poisoning

- Salicylate (aspirin) overdose

What does it mean if your Bicarbonate (HCO3), Serum result is too high?

A bicarbonate level that is higher or lower than normal may mean that the body is having trouble maintaining its acid-base balance, either by failing to remove carbon dioxide 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 high bicarbonate level include:

- Severe, prolonged vomiting and/or diarrhea

- Lung diseases, including COPD

- Cushing syndrome

- Conn syndrome

- Metabolic alkalosis

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