Bicarbonate

5 mL blood in lithium heparin or plain tube.

Spectrophotometry (measures total CO₂); derived parameter in blood gas analysis.

See Table 6.

Acid-base disorders; particularly as initial investigation of metabolic abnormalities and in defining renal tubular acidosis.

Serum bicarbonate is increased in metabolic alkalosis and in compensated respiratory acidosis.

Levels are decreased in metabolic acidosis. An artefactual decrease occurs if the collection tube is only partly filled, or left uncapped, due to loss of CO₂.

The terms 'bicarbonate' and 'total carbon dioxide' are often used interchangeably. Although 'bicarbonate' is 1-2 mmol/L lower than total carbon dioxide this difference is not clinically significant.