RELIABLE AND VERY SENSITIVE FLOW-CYTOMETRIC METHOD FOR COUNTING LOW LEUKOCYTE NUMBERS IN PLATELET CONCENTRATES

Reduction of leucocytes in blood components, achieved by filtration, m ay reduce the risk of HLA alloimmunization, virus transmission, and fe brile reactions. Nevertheless, white blood cell (WBC) concentrations o btained in this way can be too low to be accurately counted with autom ated and manual techniques. We describe here a rapid, reliable, and ve ry sensitive method for counting low leucocyte numbers using flow cyto metry. WBC nuclei are labelled by propidium iodide. A known amount of fluorescein- and phycoerythrin-conjugated beads (Standard Brite, Coult er) is added as an indicator of the examined volume. The time required for analyzing one tube is approximately 5 min. This method was first validated by comparing WBC counts (120-2,570/mu l) assessed on a haemo cytometer (Burker) and by flow cytometry. The second step was to deter mine the sensitivity of the method: we diluted normal platelet concent rates with phosphate-buffered saline. The comparison of expected with observed values showed a very good correlation up to a concentration o f 1 WBC/mu l. This technique is an accurate method that can be applied in blood bank quality controls and in clinical studies.