Studies on the characterisation of the cause of leucoreduction failures, with particular reference to extra gatal events

The causes of leucodepletion failure are multifactoral and can be related to haematological variability in blood donors or donation, defective filters, poor specimen handling or ageing, and/or the presence of non-adhering leucocyte/platelets. Since refiltering removes all types of leucocytes, including the populations appearing as extra gated events, we have developed a practical method for refiltering the failed leucodepleted components on standard filters and back-flushing the second filter to assess the nature of the WBC sub-population. In practice, recovered leucocytes from red cell filters and whole blood mainly consist of neutrophils. Those from platelet and plasma filters were mainly lymphocyte with considerable differences depending on the type of leucodepletion process. Atypical leucocytes are often seen in some pre-/post-cellular leucofiltered components. These appear characteristically as small WBC with a lower affinity for filter matrix, or as cell fragment, pinched leucocyte or apoptotic cells. Different reagents in use show variable sensitivity in identifying these extra gatal events. Storage of leucodepleted samples also induces different types of abnormality in leucocyte dot plot. A useful practical approach for characterisation of the nature of leucocyte sub-populations causing failure in leucodepleted components is provided.