Bicarbonate

Serum bicarbonate is closely related to the metabolic acid-base status of the patient. In nearly all circumstances a low serum bicarbonate indicates a metabolic acidosis and high serum bicarbonate indicates a metabolic alkalosis. Note that these changes may primary or secondary (compensatory) to primary respiratory disorders. For example a primary respiratory acidosis (under-ventilation) produces high levels of hydrogen ions in the blood (academia) which leads to renal retention of bicarbonate and elevated serum bicarbonate reflecting the metabolic alkalosis induced to attempt to correct the primary disorder.

Low serum Bicarbonate (metabolic acidosis)

Bicarbonate concentrations in the serum may fall due to consumption by combining with protons (H+) from acids such as lactic acid, keto-acids etc; or by loss from the body from gastro-intestinal or renal sources. Renal loss may be due to compensatory mechanisms for a respiratory alkalosis or renal disease, either non-specific in renal failure from any cause or due to the rarer renal tubular acidoses. Bowel causes of bicarbonate loss include diarrhoea and any cause of loss of biliary fluid.

High serum bicarbonate (metabolic alkalosis)

Elevated bicarbonate concentrations in the serum may be due to retention in the kidney in response to a respiratory alkalosis; ingestion of bicarbonate-containing fluids; or loss of hydrogen ions from the body, such as in vomiting (especially with pyloric stenosis), gastric suction, or renal losses such as with some diuretics.

Measurement