Assessing precision and accuracy in blood gas proficiency testing.

Blood gas proficiency testing has focused on assessing the accuracy of measurement of each analyte (pH, PCO2) independently of each other. Recently, the American Thoracic Society-California Thoracic Society Blood Gas Proficiency Testing Survey distributed the same lot of ampules of proficiency testing material (a buffered fluorocarbon-containing emulsion) on three occasions within a 1-yr period, allowing us to assess the precision (reproducibility) of measurement of each analyte. Comparing 580 instruments of 13 models, we found that the precision of measurement of each analyte was positively correlated with the precision of measurement of each other analyte, and the correlation of precision between models was much stronger than precision between the individual instruments. We also found correlation of precision of each analyte with two targets for accuracy: (1) the all-instrument mean and (2) the model-specific means. Correlations were higher with the model-specific means. These findings suggest: (1) that features unique to design of each model are important in the precision of measurement of these ampules, and (2) that it would be informative to include measurements of precision with linked and cumulative ratings of analyte accuracy in proficiency testing rating systems.