Serum osmolality. A CAP survey analysis

Serum osmolality has been included as a constituent to the comprehensive Chemistry Series of the College of American Pathologists Survey Program since 1973. The data for 1975 are reviewed in depth and compared with those for the two previous years. The results show that the interlaboratory variation of osmolality analysis is minor and concurrence has shown progressive improvement each year. The mean concentrations of duplicate pairs of specimens circulated to participants in 1975 show very close agreement except for one pair of duplicates for those laboratories using the Advanced Instruments and Fiske osmometers. The source of this difference is unexplained. The mean concentrations achieved by the participants using the various osmometers were compared with the "all-methods" mean. The bias is greatest for those laboratories using the Fiske and Wescor instruments. The number of laboratories submitting osmolality data has increased each year. There has been some change in the relative popularities of the various osmometers used by the participants.