Sickle Hb polymerization in RBC components from donors with sickle cell trait prevents effective WBC reduction by filtration.

BACKGROUND: RBC components collected from donors with sickle cell trait frequently occlude WBC-reduction filters. In vitro, sickle trait RBCs have the potential for sickle Hb (Hb S) polymerization at low oxygen saturations and high Hb concentrations. STUDY DESIGN AND
METHOD: To determine if the low pH and high osmolarity of the CP2D used in the collection contributed to filter failures, the filterability of sickle trait donor RBCs collected in CP2D was compared with RBCs from the same donors collected in heparin.
RESULTS: Five of six sickle trait components collected in CP2D did not complete filtration, but all six RBC components collected in heparin filtered completely. RBC components collected in CP2D from four other sickle trait donors were divided in two, and one-half was treated with carbon monoxide to convert Hb S to its liganded form to prevent Hb S polymerization. All four carbon monoxide-treated components filtered within 9 minutes, but only one untreated component filtered completely. RBC components collected by apheresis contained less CP2D, and five of seven sickle trait apheresis components filtered completely; four of the five filtered rapidly (<15 min) and one filtered in 100 minutes. Hb oxygen saturation was greater in the four rapidly filtering apheresis RBC components (68 +/- 9%) than in the three that filtered slowly or incompletely (37 +/- 5%, p = 0.03).
CONCLUSIONS: Hb S polymerization appears responsible for RBC WBC-reduction filter failures. Citrate anticoagulant and low oxygen saturation are responsible in part for Hb S polymerization in this setting.