Accurate quantitation of the low number of white cells in white cell-depleted blood components

A simple method of accurate quantification of low concentrations of white cells (WBCs) in WBC-depleted blood components was developed by using propidium iodide (PI) to stain the nuclei of WBCs. The method was validated by correlating the PI-determined WBC concentrations with those determined with Coulter S-plus IV counter in units of packed red cells (PRBCs) or random-donor platelets (RDPs). The correlations were linear and had coefficients of 0.99. The sensitivity of PI staining permitted the detection of concentrations of WBCs as low as 1 cell per microL of RDPs or 11 cells per microL of PRBCs. Therefore, PI staining will be useful in investigating the role of transfused WBC-depleted blood components in the prevention of primary alloimmunization to HLA antigens, as well in evaluating various new procedures with high efficiency in depleting WBCs from blood components.