Matrix effects in blood gas proficiency testing.

Materials currently used for blood gas proficiency testing are unlike whole blood in several obvious respects, which by definition introduces matrix effects as possible sources of error that can affect proficiency testing results. Data from recent College of American Pathologists surveys are reviewed and aqueous and fluorocarbon matrices for PO2 and PCO2 testing are compared. Closely related to matrix effects are other sources of error unique to proficiency testing samples, such as sample temperature and sample packaging. Proficiency testing programs are seriously hampered by not being able to use either whole blood or a better surrogate than is currently available. In particular, the use of aqueous materials has the potential to penalize participant laboratories unfairly in some cases and to turn proficiency testing into a meaningless exercise in others.