The Clinical Detection of Variations in the Concentrations of Normal Leukocyte Types:

Abstract

This study represents part of a clinical evaluation of the ADC500 automated leukocyte differential counter: 100-cell manual eye-counts on wedge smears prepared in a semi-automated fashion were compared with automated 500-cell counts on spun smears, and normal ranges of total cell concentrations were established for both methods. For each method, and in an unselected consecutive patient population, variations in total cell concentrations by cell class were recorded and analyzed as to their differences from established normals and the degree of significance of their differences. The data show that the automated method is in good agreement with manual counts, but detects variations in concentration with a greater degree of confidence, when comparisons are made with normality. This is presumed to be at least partially due to a reduction of within-slide statistical sampling error. However, it may also reflect the nonrandom and irregular distribution of cells on the wedge smear and the nonrandom search pattern conducted by the technologist during manual eye-counts. Differences in the distributions of normal values for monocytes by method are noted. An increased sensitivity of the ADC500 to monocytosis and lymphocytopenia is described. Improved reporting formats for automated imaging systems are discussed based upon the approach taken in this study. The clinician should be provided with data in the form of absolute cell concentrations, with an indication of the unique within-specimen statistical variation affecting the result, and finally, if the measurement varies from normality, the degree of confidence in the variation. This approach only addresses methodological variation. As others have pointed out, physiologic diurnal variations in leukocyte concentrations are significant and must be considered in relation to the timing of phlebotomy and the ultimate interpretation of any detected variations in concentration.Key WordsTotal leukocyte concentrationsAutomated differential instrumentationData reportingClinical interpretation