Platelet activation during storage of platelet concentrates processed from buffy coats by the automated OrbiSac system

We read with interest the article by Vetlesen and colleagues describing a comparison of platelet (PLT) quality during the storage of buffy coat (BC) PLT concentrates (PCs) prepared either manually or by an automated system (OrbiSac system, Gambro BCT, Karlskoga, Sweden). The authors highlight the finding of a higher expression of surface CD62P on resting PLTs in the automated OrbiSac PCs (A-PCs) compared to the manually produced PCs (M-PCs). In previously reported results, our group observed more PLT activation in A-PCs, although the difference was not significant. In this regard, we noted that on Day 2 CD62P expression was much higher in both groups (A-PCs and M-PCs) compared to results by Janetzko and colleagues. Like Vetlesen and colleagues, we also think the slightly greater PLT activation is not of major clinical importance, but it may be a matter of concern. Trying to think of how to reduce it, we realized that in our component laboratory the first event that increased activation was the implementation of a PLT additive solution (PAS) instead of plasma as storage medium for PCs. This change was not associated with clinical problems in patients; in contrast, the use of PAS-2 (SSP, Macopharma, Tourcoing, France) resulted in fewer transfusion-related reactions. The effects on PLT metabolism and function associated with different components in PAS are only partly known, so we decided to test different ASs and compared them only in A-PCs. We tried to check whether PASIIIM (SSP+, Macopharma) or Composol (HemoCare GMBH, Bad Homburg, Germany) offered in vitro advantages over our routine medium for PLT suspension (PAS-II, SSP, Macopharma). We studied 25 A-PC–produced BC PCs, consisting of 8 with PAS-II, 8 with PASIIIM, and 9 with Composol PS. During processing of whole blood, we used top-and-bottom bags (Composelect Bioflex—Rcc soft filter; Fresenius HemoCare, Emmer-Compascuum, the Netherlands), separating into plasma, RBCs, and a BC. We sterile docked a bag with 300 mL of PAS and four ABO-identical BCs to an OrbiSac standard BC set. We recorded the following data: A-PC volume, PLT and WBC count, swirling and pH, and CD62P expression on Days 2 and 6. For statistical analysis a t test and Pearson’s chi-square test were applied with the use of a software program. A probability of a p value of less than 0.05 was used to reject the null hypothesis. PLT counts were similar: 0.88 ¥ 10 0.1 ¥ 10 per BC (in the PAS-II group), 0.94 ¥ 10 0.13 ¥ 10 per BC (in the Composol-PS group), and 0.89 ¥ 10 0.12 ¥ 10 per BC (in the PAS-IIIM group). No intergroup differences were detected in terms of volume, swirling, WBC count, or hemoglobin content. pH was lower on Day 6 in the PAS-II group compared to the Composol-PS or PAS-IIIM groups. CD62P expression on Days 2 and 6 was higher in the PAS-II group compared to the Composol-PS or PAS-IIIM groups (Table 1). Our blood bank produces 80-90 BC PCs daily. Since 2004, the blood bank has produced only A-PCs, because of the greater PLT yield. In our opinion, it is difficult to achieve these results in terms of PLT content with a manual method in a routine way, especially when using an AS that generates a highly sensitive layer. In recent years there have been major advances in automation, which we feel is the right path to follow. Nevertheless, activation with high CD62P expression occurs. We agree with Vetlesen and colleagues that the logical explanation may be the shear stress to which PLTs are subjected during the automated production process. In our experience, swirling is not observed until 1 to 2 hours after A-PC collection. As Vetlesen and colleagues stated, activation does not seem to be a major clinical problem. We believe that PLT activation may be prevented using a PAS-containing potassium and magnesium, such as PAS-IIIM and Composol-PS.