About 75 million units of whole blood are collected from donors worldwide each year. On any given day, tens of thousands of units of blood are needed for accident victims, surgical patients, and patients with diseases such as a leukemia or sickle cell disease.

Typically, each unit of whole blood is separated into multiple components: red blood cells, plasma, and platelets. The presence of leucocytes (white blood cells) in blood and platelet products has been shown to be associated with an increased incidence of transfusion reactions in patients receiving blood products.

Leucoreduction, removing leucocytes, requires a process to evaluate the amount of residual leucocytes remaining in a blood product, and flow cytometry is a preferred method for this evaluation. The BD Leucocount™ assay is a flow cytometric method for counting residual leucocytes in blood products that are processed for transfusion.