FlowScore

Summary of article published in The Lancet, full article can be viewed here.

The study “Assessing the kinetics of oxygen-unloading from red cells using FlowScore” introduces a new tool, FlowScore, which is a flow-cytometric surrogate for assessing the functional quality of red blood cells (RBCs) in terms of oxygen unloading. Unlike traditional methods that measure oxygen-carrying capacity using hemoglobin assays, FlowScore focuses on the kinetics of oxygen release, a critical aspect for tissue oxygenation.

Oxygen unloading depends on the diffusion path-length inside RBCs, which is influenced by the cell’s geometry. The researchers developed FlowScore by relating the time constant of oxygen unloading (τ), measured through single-cell oxygen saturation imaging, to flow-cytometric variables like side-scatter and forward-scatter recorded by standard haematology analyzers. This metric was found to distinguish freshly drawn blood from stored blood, where metabolic depletion and changes in cell geometry hinder oxygen unloading.

FlowScore demonstrated over 80% sensitivity and specificity in identifying changes in oxygen unloading rates due to blood storage. Furthermore, it accurately predicted the restoration of oxygen unloading upon biochemical rejuvenation (Rejuvesol) of stored blood. The metric’s reliability was confirmed across four international blood banks in Australia, Canada, England, and Spain. Additionally, FlowScore was able to estimate ATP and 2,3-diphosphoglycerate (2,3-DPG) levels, important for RBC function, by assessing RBC geometry and metabolic status.

The study applied FlowScore to large datasets from the LifeLines and COMPARE studies, revealing factors like age, sex, and smoking that affect RBC oxygen handling. The tool is positioned as a cost-effective and accessible means for assessing RBC quality in blood banking and haematology, offering a likely solution to a significant gap in blood storage monitoring.

In conclusion, FlowScore offers a valuable, scalable approach for evaluating RBC oxygen unloading kinetics, which could improve the understanding of RBC quality beyond traditional hemoglobin-based assessments. It is particularly useful for identifying storage lesions, offering a reliable surrogate for oxygen unloading kinetics, and has the potential to enhance blood transfusion outcomes.