Clinical and Interpretive

The bicarbonate content of serum or plasma is a 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-base 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. Bicarbonate is the second largest fraction of the anions in
plasma. Included in this fraction are the bicarbonate (HCO3) and carbonate (CO3) ions, carbon dioxide in physical solution, as well as the carbamino compounds. At the physiological pH of blood, the concentration of
carbonate is 1/1000 that bicarbonate. The carbamino compounds are also present in such low quantities that they are generally not mentioned specifically.

Alterations of bicarbonate and CO2 dissolved in plasma are characteristic of acid-base imbalance. The nature of the imbalance cannot, however, be inferred from the bicarbonate value itself, and the determination of bicarbonate is rarely ordered alone. Its value has significance in the context of other electrolytes determined
with it and in screening for electrolyte imbalance.

Because the determination of bicarbonate actually includes dissolved CO2, this fraction will escape from the specimen into the air once the stopper is removed from the vacutainer tube. The rate of change in the bicarbonate determination is approximately 6mmo1/L in the course of 1 hour.