The effect of storage on platelet morphology

Platelet concentrates were stored for one, two or three days at 4 degrees C (unagitated) or at room temperature (unagitated and linearly agitated). After washing the concentrates twice at room temperature and then incubating them for 60 minutes at 37 degrees C, the platelet morphology was investigated by scanning and transmission electron microscopy. Platelets in freshly prepared concentrates were slightly activated, indicated by some pseudopod formation. Platelets stored at 4 degrees C rapidly lost the normal discoid shape. After three days of storage their surface membranes showed extensive folding, they were slightly vacuolated, and had lost most of their granules. Incubation of cold-stored platelets at 37 degrees C did not induce return to the discoid shape. Room temperature storage resulted in reversal of the slight initial platelet activation. After three days of unagitated room temperature storage the platelets were slightly more vacuolated than those stored with agitation. Room temperature storage usually resulted in well-preserved discoid platelets; however, some agitated platelet concentrates stored at room temperature contained a high proportion of odd shaped cells. This finding could not be correlated with pH change. The failure of platelets stored at 4 degrees C to return to the discoid shape after incubation at 37 degrees C could explain their short survival following transfusion. These results also provide a morphologic correlation with the reported slightly better recovery and survival of platelets stored at room temperature with agitation compared with those stored without agitation.