Ultrastructural changes in stored platelets

A wide variety of lesions develop in blood platelets stored in vitro for long periods of time. Most of them reflect activation and damage caused by lack of gas exchange across the wall of the container and a fall in pH below 6. Newer bags facilitate O2/CO2 exchange and maintain a neutral pH. As a result, most of the lesions reflecting acidic damage or destruction have disappeared. Some storage lesions persist, however. Formation of platelets resembling doughnuts occurs in the first 24 or 48 hours after collection and concentration. They are infrequent in currently used bags. Giant alpha granules resulting from fusion of normal-sized organelles, however, are not rare. They appear as early as 4 to 5 days, even under the best conditions, and increase in frequency up to 14 days. The basis for their development remains obscure.