A parallel evaluation was performed on four automated hematology analyzers: the Celldyn 3000 (Unipath Corp., Mountain View, CA), the Coulter STKS (Coulter Electronics Inc., Hialeah, FL), the Sysmex NE-8000 (Baxter Healthcare Corp., McGaw Park, IL), and the Technicon H*2 (Miles Corp., Tarrytown, NY). The protocol included evaluation of the complete blood count and differential leukocyte count (DLC) parameters. The DLC evaluation was performed using the National Committee for Clinical Laboratory Studies H20-A protocol. Based on this evaluation, the authors could not identify a single instrument that was clearly superior to the others. Overall, the four instruments were found to be safe and effective for diagnostic use; however, there were areas in which their performance was less than optimal. Particular questions were raised regarding the clinical usefulness of instrumental "flags" to identify qualitative leukocyte abnormalities. The results are discussed in relation to the selection of instruments for specific clinical applications.

Transplant centers often rely on CD34+ cell quantitation by flow cytometry to ensure adequacy of hematopoietic progenitor cell collection. Because of variation in interpretation, a lack of interlaboratory proficiency studies, and no generally accepted methodology, comparison of CD34 data from site to site is difficult. Twenty-one samples from marrow and peripheral blood stem cell collections were shipped to 10 participating North American laboratories for analysis. Duplicate samples were included to assess reproducibility. Participants were surveyed for methodology. Three centers had previously attempted to standardize their methodology among themselves. The variability observed in the CD34 values ranged from a max/min. reported value per sample of 2.9 to 749 (median 76). Exclusion of two outlying sites reduced the variability of results to 1.2 to 27 (median 3.1). Variation among the three standardized sites ranged from 1.2 to 4.4 (median 1.6). Overall reproducibility (excluding the outlying sites B and G) ranged from a minimum of 0-16.5 (percent mean difference) for site C to a maximum of 4.1-133 for site H. Strategies for gating were found to largely influence results. We observed an alarming variation among the CD34 cell counts reported from different laboratories. Standardization substantially reduced observed variation. The need for standardized methodology, reporting, quality control, and proficiency testing is underscored by these findings.

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An automated complete blood count with white blood cell differential was performed yearly on successive groups of healthy second-year medical students from 1979 through 1987. For three classes (1984-1987), the counts were repeated on the same people nine months later. These data demonstrated that the mean value of all hematologic parameters was quite stable over nine years. This allowed for an estimation of the upper limit for the combined effects of drift in accuracy, precision, and biologic stability. The stability was achievable despite an evolution in technology and quality assurance methods over that period. A comparison of intraindividual versus interindividual variation demonstrated that a normal range based on population statistics may be less sensitive than a normal range established for a person during routine health maintenance, especially for the platelet count.

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