Monthly interlaboratory pH and blood-gas survey. Establishing accuracy based on interlaboratory performance

The authors describe an interlaboratory survey provided by their laboratory which enables participants to establish an accuracy base for pH and blood-gas determinations. Data collected from 131 laboratories provide insight into state-of-the-art performance capabilities. The percentile ranking system presented may be used by individual laboratories to determine their need for improvement or to set intralaboratory performance goals. Data accumulated from 18 months of interlaboratory surveys are used to establish performance levels at three concentration ranges each for pH, pCO2, and pO2. By characterizing average errors on a percentile ranking basis, the authors enable participants to assess their performance compared with peer laboratory results. For samples with normal pCO2 levels, 95% of reported laboratory results have an error of 4.5 mmHg or less. Similarly, 95% of reported results for normal pO2 samples have an error of 13 mmHg or less, and 95% of the pH results, independent of level, have an error of 0.05 pH units or less.