Sample preparation variation and its effects on automated blood cell differential analysis.

Uniform and reproducible sample preparation is an indispensable ingredient in automated instruments for cell analysis. Differences in measured cell morphology resulting from nonuniform sample preparation are indistinguishable to the instrument from differences reflecting different cell types or functions. As a result, as sample preparation becomes more variable, subtle cell distinctions are first confused and then completely obscured. As part of the development of the Abbott ADC-500 differential analysis system, automatic blood film spinner and stainer modules were developed to provide uniform sample preparation. These modules were tested to quantitate the effects of variations in the spinning and staining conditions on the measured ADC-500 parameters and observed cell morphology. The previously reported increase in spin time with increasing hematocrits was confirmed for the ADC-500 spinner. Moderate variations in spin speed, acceleration, deceleration and spin chamber configuration were found to have little or not effect. Postspinning air flow over the slide had a dramatic effect on morphology distortion. Variations of the staining temperature, staining time or rinse volume were found to have very little effect on measured leukocyte parameters although staining temperature had a dramatic effect on observed erythrocyte morphology and staining. Stain:buffer ratio variations were found to alter measured leukocyte parameters, with the measured density increasing as the fraction of stain increased up to a 1:2 stain:buffer ratio. Because the operational limits for the spinning and staining parameters are much tighter than the range of variables investigated, it was concluded that the ADC-500 sample preparation modules do not introduce variations in the analyzer results.