Multicenter Evaluation of Methods for Counting Residual White Cells in Leukocyte‐Depleted Red Blood Cells

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Abstract
Two wet workshops were conducted involving 20 laboratories to determine optimum methods for counting residual white blood cells (WBC) in leukocyte-depleted red blood cells (RBC). In both studies, calibration samples containing known concentrations of WBC were prepared by diluting 1-day-old EDTA blood in RBC virtually free of WBC. Study No. 1 was aimed at determining the lower limit of detection and at examining advantages and disadvantages of two methods based on flow cytometry (FC) and on the Nageotte chamber (NC), respectively. This study showed that the lower detection limits for FC and NC were 0.1 and 1 WBC/microliters, respectively. Methods based on FC showed less variability at 0.1-1 WBC/microliters but were equal in performance to counting procedures based on the NC above 1 WBC/microliters. We then designed study No. 2 to evaluate three different protocols using the NC. In protocol 1, samples were diluted 1:10 with Plaxan and with Türk's solution; in protocol 2 a mixture of Türk's solution and Zap-oglobin, a reagent used in manual hemoglobin determinations, was used to dilute the samples 1:5; and protocol 3 involved initial 1:10 dilution of a 1-ml sample with Plaxan followed by WBC concentration into the original 1-ml volume by centrifugation. In each participating laboratory, two technologists independently processed the samples and read the results with an NC. Plaxan and Türk's solution gave comparable results. Interobserver variability was not critical to the results. All three NC methods were valid for counting at concentrations of > or = 1 WBC/microliters.(ABSTRACT TRUNCATED AT 250 WORDS)