Emedinews:Tat Tvam Asi:Leukocyte-reduction filters

Tat Tvam Asi……..and the Life Continues…..

(Dr N K Bhatia, Medical Director, Mission Jan Jagriti Blood Bank)

Special “third-generation” blood filters can reduce the number of leukocytes in red cell or platelet components of less than 5x10, a level that reduces the risk of HLA alloimmunization and transmission of cytomegalovirus (CMV) as well as the incidence of febrile transfusion reactions. These filters contain multiple layers of synthetic non-woven fibers that selectively retain leukocytes but allow red cells and platelets to pass. Selectivity is based on cell size, surface tension characteristics, the difference in surface charge density among blood cells, and possibly, cell to cell interactions and cell activation/adhesion properties.

Because filters for red cells and filters for platelets do not use the same technology for leukocyte removal and may have strict priming and flow rate requirements, they must be used only with their intended component and only according to the manufacturer’s directions. The use of these filters at the bedside is more complex than the use of standard infusion sets. The filters are expensive and will be ineffective if improperly primed or used. Those designed only for gravity-drip infusion should not be used with infusion pumps or applied pressure.

A quality control program that measure the effectiveness of leukocyte reduction helps monitor the filter or system in place, and is especially important with bedside filtration. Routine methods of automated blood cell counting are not sensitive enough to enumerate the small numbers of leukocyte in leukocyte reduced components; the use of high volume manual counting chambers or flow cytometric procedures is preferred.