Comparison of Measured and Calculated Bicarbonate Values

Patient acid–base status may be assessed by measuring bicarbonate (HCO3−) in serum or plasma from a sample of venous blood. HCO3− values are also frequently calculated from pH and CO2 partial pressure measurements obtained during arterial blood gas (ABG) analysis. To determine whether measured and calculated HCO3− values can be used interchangeably and to determine whether a comparison of measured and calculated HCO3− values can be used to detect errors in the collection or analysis of blood samples, we compared measured (venous) and calculated (arterial) HCO3− concentrations for arterial and venous samples drawn at the same time. We also reproduced common preanalytical errors in the laboratory to evaluate their effect on the relationship between calculated and measured HCO3− concentrations. We obtained 17 621 records of both measured and calculated HCO3− concentrations for samples drawn simultaneously from the same patients between October 2006 and July 2007. Calculated HCO3− concentrations were obtained from ABG samples drawn into …