Morphological changes associated with pH changes during storage of platelet concentrates.

The platelet injury and loss of viability that has been shown to occur with storage of platelet concentrates (PC) under conditions with increasing or falling pH were examined using scanning and transmission electron microscopy. After storage of PC in first (PL-146) and second generation containers (PL-1240 and PL-732), samples were taken for measurement of pH value, platelet count and size distribution, release of lactate dehydrogenase (LDH) into plasma, and for SEM and TEM. After storage of 83 PC in first generation containers for 4 days increased levels of LDH were observed in PC with pH above 7.3 (n = 2) and below 6.1 (n = 4). The electron microscopic pictures confirmed previous suggestions that platelet disc-to-sphere transformation and cytoplasmic swelling occur when pH falls below 6.7-6.8 during storage. In PC with pH below 6.1 the morphological change was irreversible with the appearance of more than 90% lysed and balloon platelets. In PC with pH above 7.3 because of low platelet concentration this was related to an increased number of platelets that were lysed of had a swollen disintegrated internal structure (balloons) as seen with TEM. SEM and Coulter counter studies also showed that platelet fragmentation and formation of microvesicles were prominent in PC with pH above 7.3. Second generation containers maintained the pH during 5-day-storage at higher levels but had enhanced risk of pH increase. A strong tendency for the platelets to become alkaline upon subsequent storage could be demonstrated as a result of excessive forces or prolonged centrifugation during the second spin of the preparation procedure. Whereas the platelet injury caused by low pH is easy to recognize because of the absence of swirling the morphological changes associated with high pH cannot be detected directly.