Studies on the ultrastructure of blood cells and the microaggregate fraction in stored human blood

Electron microscopy of citrate-phosphate-dextrose (CPD) buffered bank blood performed over 21 days shows that the normal architecture of erythrocytes, platelets and leucocytes disappears and that deformed organelles, leucocyte "ghosts", cell fragments and microaggregates accumulate. Leucocytes and platelets emerge as the most sensitive indicators of blood deterioration showing profound morphological changes from the first day. Microaggregates which passed through a 20-micrometer high capacity transfusion filter were identified as platelet conglomerates, leucocyte "ghost" and platelet-leucocyte "ghost" coaggregates with diameters of 6--20, 20--30 and 30--40 micrometers respectively. Of these aggregates present in the filtrate, 62% fell into the size range of 20--40 micrometers. The composition of microaggregates varies with storage time, the platelet conglomerates appear first during or after Day 1, leucocyte "ghosts" after Day 5 followed by platelet-leucocyte "ghost" coaggregate formation. At this stage the number of intact leucocytes and platelets is reduced and the filtrate shows an abundance of leucocyte debris. Microfiltration would thus appear to reduce but not eliminate the danger of microembolism and damage to capillary endothelium.