In vitro and In vivo Evaluation of Platelet Concentrates after Cotton Wool Filtration

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Abstract
Removal of leukocytes from platelet concentrates (PC) may decrease the incidence of alloimmunization to HLA antigens on white cells and prevent or delay refractoriness. Cotton wool filtration, which effectively removes leukocytes from PC with minimal platelet loss, may cause platelet or complement activation. In this study, the effect of cotton wool filtration (Imugard IG-500) on platelet activation, in vitro function, posttransfusion survival, and complement activation was investigated. Five paired autologous in vivo percent recovery and survival studies were performed with fresh (6-8 h) PC or with 5-day-stored PC prepared from CPD-anticoagulated blood and stored in PL-732TM containers using standard methods. In the paired design, PC from the same donor were filtered on one occasion, and not filtered on another, prior to labeling with indium-111-oxine and reinfusion. Percent recovery and survival were then determined by the standardized method. Filtration had no statistically significant effect on percent recovery on PC stored for 6-8 h or for 5 days. There was, however, a slight decrease in survival hours of the filtered PC which was statistically significant at 6-8 h (203 .+-. 14 vs. 179 .+-. 18 h; p < 0.05) but not at 5 days (166 .+-. 28 vs. 132 .+-. 27 h; p > 0.05). Samples taken before and after filtration of single units (fresh and 5-day) and pooled units (3-day) for measurement of release of granular content (.beta.-thromboglobulin), lysis (LDH), and in vitro viability - ATP, extent of shape change with ADP, and hypotonic shock response (3-day only) - demonstrated no effect of filtration on these parameters. A slight, but significant (p < 0.05) increase in plasma levels of C3a was found for fresh-filtered PC, but not for stored PC, suggesting some complement activation during filtration.