This revised Phase I STTR application is focused on providing proof-of-concept for a novel, high throughput, completely automated assay for routine quality control (QC) monitoring of residual leukocytes (rWBCs) in filtered blood prior to transfusion. As the use of filter leukoreduction increases, and accumulating data suggests that filter failures can lead to morbidity in transfusion recipients, the FDA may implement more rigorous QC guidelines to confirm that rWBCs have been reduced to below acceptable levels (5 x 10(6)) in filtered blood components. Should QC requirements increase significantly, manual Nageotte hemocytometry will no longer be a feasible method for counting rWBCs. While flow cytometry represents an alternative approach, standard cytometers are expensive (>$100,000), particularly since they must be operated manually. 3Ti is fabricating a completely automated immunohematology-testing platform that incorporates an inexpensive, small-footprint flow cytometer (funded through previous STTR grants). The objective of the proposed studies is to develop an accurate, cost-effective, high-throughput rWBC assay for this workstation. In Specific Aim #1, we will optimize the staining reagents for accurate quantitation of rWBCs with this flow cytometer. In Specific Aim #2, we will integrate the rWBC counting assay onto the automated workstation. If the proposed studies result in an automated rWBC counting assay that demonstrates sufficient accuracy, throughput, and cost-effectiveness, Phase II funding will be sought to conduct multicenter clinical trials with the objectives of further validating and commercializing this system. Successful completion of this work will lead to the first completely automated workstation for rWBC counting, and further demonstrate the utility of this multifunctional platform for walk-away automated testing in blood centers and transfusion services. [unreadable] [unreadable]