FlowScore – a formula developed at Oxford University in collaboration with NHS Blood and Transplant – predicts how quickly red blood cells release their oxygen. This process is important for oxygenating the body’s tissues, including organs and muscles, particularly in people receiving large transfusions.
Healthy fresh red blood cells have a distinctive biconcave – or dumbbell – shape for efficient oxygen release. During refrigerated storage, red cells become energetically stressed and more spherical, which slows oxygen release. Using transplant kidneys, researchers at Oxford showed that perfusion with blood units that had undergone storage-related kinetic rundown was associated with poorer oxygen delivery, and that this could be restored by biochemically rejuvenating – or refreshing – the blood.
Factors affecting oxygen release from red cells were described at Oxford’s Department of Physiology, Anatomy, and Genetics but the testing method was too laborious for routine use in blood agencies working to improve the monitoring of blood stored for transfusion. To adapt the research findings to blood banking, NHS Blood and Transplant’s Component Development Laboratory joined the project, providing blood samples stored according to NHS protocols and measurements from haematology analysers.
During routine blood counts, haematology analysers use flow cytometry – a method that passes cells through a laser beam to study their characteristics. When light hits a cell, the pattern of scattering reveals information about their size and shape. It was found that this information accurately predicts oxygen release from red blood cells, and the predictive formula was called FlowScore. The innovation makes measurements of red cell oxygen transport simpler, faster, and more accessible for laboratories worldwide.
Blood banks can now use FlowScore as a quality-control measure during processing and storage. For example, FlowScore was able to quantify the beneficial effects of rejuvenation and detect periods of blood handling outside blood bank-grade conditions. The latter may be critical in monitoring stored blood quality in developing countries with higher ambient temperatures. FlowScore could also provide a way to check the quality of blood for specific vulnerable patient groups, should future research show patient benefit.
Professor Pawel Swietach, Professor of Physiology at Oxford University, said: ‘We find that FlowScore is a robust surrogate of oxygen-handling by red cells and provides new and important information on oxygen transport by the blood. Aside from its applications in transfusion medicine and blood banking, FlowScore can help identify new genetic, environmental and lifestyle factors that influence oxygen delivery to tissues.’
Dr Peter Smethurst, from the NHSBT Blood and Transplant Component Development Laboratory, said: ‘FlowScore could become quite fundamental to the way blood is tested to ensure its quality. It is a technical breakthrough that should improve the monitoring of stored blood and drive improvements that will most benefit vulnerable recipients of red cell transfusions.’
Dr Rebecca Cardigan, Head of the NHSBT Blood and Transplant Component Development Laboratory, said: ‘FlowScore is an accessible marker of cellular performance to complement other quality metrics. It has been very exciting to conduct this cross-disciplinary and multi-agency collaboration, translating the excellent basic research in Oxford to provide a basis for better assessment of stored blood and transfusion practice across the world.’
The study, ‘Assessing the kinetics of oxygen-unloading from red cells using FlowScore, a flow-cytometric proxy of the functional quality of blood‘, is published in eBioMedicine.
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