Pseudohypobicarbonataemia.

Arterial blood gas (ABG) is obtained to assess acid-base disturbances, measure arterial oxygen (PO2) and arterial carbon dioxide (PCO2). ABG uses blood gas analysers, which have electrochemical sensors, to calculate plasma bicarbonate (HCO3), from the pH, PCO2 and PO2. Bicarbonate levels can also be measured on routine electrolyte studies such as the basic metabolic panel (BMP) or comprehensive metabolic panel. These methods typically use enzymatic/electrode methods to calculate bicarbonate levels. Generally, there is an acceptable correlation between the bicarbonate measurement from blood gas and from metabolic panel. Rarely, there is a discrepancy. The following is a case of pseudohypobicarbonataemia, where BMP consistently showed hypobicarbonataemia and ABG revealed normal levels.