Variables determining blockage of WBC-depleting filters by Hb sickle cell trait donations

Sickle cell trait donations can block leukodepletion (LD) filters or fail to LD, but the variables affecting blockage are unclear.

To identify critical variables for further study, the relationship was investigated between filter blockage and donor characteristics, processing conditions, PLT and coagulation system activation, and microvesicle formation in donations with (n = 63) and without (n = 40) sickle trait. With eight filter types whole blood was LD either at ambient temperature on Day 0 or after overnight 4 degrees C hold. Markers of PLT activation (CD62P and CD63 expression and soluble CD62P) and coagulation activation (activated FXII and prothrombin fragment 1 + 2 [F1 + 2]), RBC microvesicles, blood gases, and residual WBCs were measured.

All Day 0 filtrations blocked (n = 7). On Day 1, no filter tested was 100 percent successful, with most achieving an approximate 50 percent success rate. Two filters blocked consistently and an additional filter did not block, but resulted in 50 percent of units with high residual WBC counts (30 x 10(6)-394 x 10(6)/unit). Day 1 filtration was not improved if performed at 4 degrees C. Donor RBC variables and prefiltration measures varied little between blocked and successful filtrations except pO2, where 9 of 17 blockages had a pO2 of less than 5.0 kPa, compared with 0 of 13 completed filtrations. F1 + 2 levels increased after filtration in sickle trait units, a consequence of slow flow rate.

Filter blockage in sickle trait donors cannot be predicted by donor characteristics or filter type and is not related to PLT or coagulation activation, but can be reduced by storing units at 4 degrees C before filtration.