How effective are leukocyte reduction filters in removing white blood cells from donor blood?

Leukocyte reduction filters are used to remove > 99.9% of leukocytes. According to a Circular of Information from the AABB, American Red Cross, America’s Blood Centers, and the Armed Services Blood Program, leukocyte-reduced units of red blood cells must have a residual content of leukocytes <5.0 x 10⁶.