Bicarbonate (HCO3−), Blood

Bicarbonate is an indicator of the buffering capacity of the blood. Low bicarbonate indicates that a larger pH change will occur for a given amount of acid or base produced.

Bicarbonate in the blood is calculated from the pH and PCO2 using the Henderson-Hasselbalch equation.

Normal range:

Arterial: 21 " пїЅ28 mEq/L

Venous: 22 " пїЅ29 mEq/L

Use

Significant indicator of electrolyte dispersion and anion deficit.

Together with pH determination, bicarbonate measurements are used in the diagnosis and treatment of numerous potentially serious disorders associated with acid " пїЅbase imbalance in the respiratory and metabolic systems. Some of these conditions are diarrhea, renal tubular acidosis, carbonic anhydrase inhibitors, hyperkalemic acidosis, renal failure, and ketoacidosis.

Interpretation

Increased In

Primary metabolic alkalosis

Primary respiratory acidosis

Severe vomiting

Lung disease (COPD)

Cushing syndrome

Diuretics

Primary hyperaldosteronism

Laxative abuse

Decreased In

Primary metabolic acidosis

Primary respiratory alkalosis

Addison disease

Ethylene glycol or methanol poisoning

Chronic diarrhea

Salicylate overdose

Limitations

Bicarbonate can be determined by titration, but this is rarely done.

HCO3 пїЅ пїЅ пїЅ is the largest fraction contributing to the total CO2. Therefore, both parameters usually change in the same direction.

The standard HCO3 пїЅ пїЅ пїЅ is the concentration of HCO3 пїЅ пїЅ пїЅ in whole blood at 38 пїЅ пїЅC equilibrated at a PCO2 of 40 mm Hg with the blood Hb fully oxygenated.