BICARBONATE

BICARBONATE - serum

Application: Acid-base disorders; particularly as initial investigation of metabolic abnormalities.

 

Explanation: Bicarbonate(HCO3-) is quantitatively the second most important anionic fraction in serum. CO2 produced by cellular metabolism diffuses into the plasma and combines with H2O inside red cells to form H2CO3 (carbonic acid). Carbonic acid dissociates to form H+ and (HCO3-). The H+ is buffered by reduced hemoglobin and as the bicarbonate concentration builds up in the red cells, it diffuses down its concentration gradient into the plasma, being replaced by Cl-. This movement of Cl- into the red cell to conserve electrical balance is called the "chloride shift". A small amount of CO2 is also carried in the blood bound to amino groups of hemoglobin. Clinically, bicarbonate and other forms of carbon dioxide are measured together as total CO2.
   

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


Specimen: 5 ml blood in red- or green-top tube.


Reference Interval:
22-32 mEq/L.