Phosphatidylethanolamine is progressively exposed in RBCs during storage.

Background: It is well established that as a blood unit ages, fewer of the unit's red blood cells (RBCs) remain in circulation post-transfusion. The mechanism for clearance is not well defined. Phosphatidylethanolamine (PE) is a phospholipid that is primarily found on the inner leaflet of healthy cells, and is an important ligand for phagocytosis of dead cells when exposed.

Objectives: The objective of the present study was to measure the change in PE exposure in donor RBCs over increasing storage ages using the novel PE-specific probe, duramycin.

Methods: Five adsol (AS-1) preserved RBC units were sampled weekly for 6 weeks and were labelled with duramycin. The percentage of PE exposed on red cells in each sample was determined using flow cytometry. Surface phosphatidylserine (PS) was evaluated for comparison.

Results: We found that RBCs in AS-preserved donor units increasingly exposed PE, from less than 1% in freshly processed RBCs, to nearly 20% at 42 days of storage and correlated with increased relative vesiculation or microparticle concentration and release of cell-free haemoglobin. By comparison, only 5% of cells exposed PS at 42 days.

Conclusion: We conclude that exposure of PE in the RBC outer membrane was higher than that of PS during 42 days of storage and correlated significantly with increased vesiculation and release of haemoglobin.