Residual aggregates in platelet products: what do we know?

BACKGROUND AND OBJECTIVES: Platelet (PLT) aggregates can occur during or after PLT component processing. However, very few reports investigating the phenomenon and its clinical significance have been published. In this review, currently available information about aggregates in PLT products is summarized and possible causal factors as well as preventive strategies are discussed. MATERIALS AND METHODS: A review of the MEDLINE® database for relevant publications from 1960 to May 2013 was conducted. RESULTS: It is well known that PLT aggregates may occur during or after the PLT product preparation process. These aggregates normally dissipate with rest and agitation. However, in some rare cases, the aggregates do not dissipate within 24 h and can persist up to the end of storage. Exposure to low temperature, low pH, short resting period after collection, different collection systems, presence of bubbles or foam inside the PLT bag, PLT-container interactions, proper product mixing and donor-dependent variables may have an impact on the formation of PLT aggregates. Although publications are rare, the presence of small numbers of PLT aggregates appears to have only limited impact on PLT in vitro quality. Furthermore, data on the clinical impact of PLT aggregates are lacking. CONCLUSION: Despite the fact that PLT aggregates occur in PLT products, published data on this topic remain scant. Considering the concern of clinicians about this phenomenon, more studies are needed which should focus on the possible clinical impact of such aggregates and precautions to avoid PLT aggregate formation in PLT products.

The Mirasol PRT system for pathogen reduction of platelets and plasma: an overview of current status and future trends.

The safety of blood transfusion is still threatened by contamination of blood products with a variety of pathogens such as viruses, bacteria and parasites. A novel pathogen reduction process for platelets and plasma products, the Mirasol PRT system, has been developed and is under clinical evaluation for its efficacy and safety. The Mirasol PRT process is based on riboflavin photochemistry. This manuscript reviews current progress and future trends.

What's happening? The expanding role of apheresis platelet support in neonatal alloimmune thrombocytopenia: current status and future trends.

Despite some unresolved problems that may be associated with platelet transfusion, such as alloimmunisation, refractoriness, bacterial contamination, and the potential side effects related to the development of some biological response modifiers during storage, platelet therapy remains the most effective treatment for the management and prevention of severe thrombocytopenia and hemorrhage [Seghatchian J, Snyder EL, Krailadsiri P, editors. Platelet therapy: current status and future trends. Amsterdam, The Netherlands: Elsevier; 2000]. This appears to be particularly the case in neonatal alloimmune thrombocytopenia (NAIT), which arises due to an incompatibility of the platelet specific antigens between the pregnant mother and her baby. Over 80% of severe NAIT cases in the Caucasian population occur when the mother and baby differ in their HPA-1 epitope (HPA-1a negative and positive respectively) leading, in 10% of cases, to the production of anti-HPA-1a which can cross the placenta and cause NAIT in utero or post-partum. Anti-HPA-5b is the second most cause of NAIT, although severe cases occur only after the first pregnancy. Clinical manifestations of NAIT vary from mild (petechia and bruises) to severe (intracranial haemorrhage with possible death or life long morbidity). A recent study in Scotland indicated that the cost per case of severe NAIT detected during screening of pregnant women, where anti-HPA-1a is detected for the first time, would amount to $98,771 [Turner M, Bessos H, et al. Prospective epidemiological study of the outcome and cost effectiveness of antenatal screening to detect neonatal alloimmune thrombocytopenia (NAIT) due to anti-HPA-1a. Transfusion, in press. Yet, unlike the case with Rhesus hemolytic disease of the new born, the cost-effectiveness of HPA-1 screening in NAIT remains unresolved, as does the most optimal mode of treatment. Therefore, in the absence of a consensus on the screening and optimal management of NAIT, the availability and provision of HPA-1a/5b negative apheresis platelets based on current practice (transfusionguidelines.org.uk) appear to be a clinically effective treatment in NAIT. In that vein, an increasing number of blood transfusion centres are screening blood donors in order to secure panels of donors for the prompt provision of HPA-1a/5b negative apheresis platelets. However, evidence is also accumulating that while platelets derived from various apheresis technologies currently in use may be equivalent in terms of cellular contents (thus meeting specifications), they may differ in terms of the platelet storage lesion, microvesiculation and the development of platelet-derived cytokines and some other biological response modifiers [Seghatchian J. Platelet storage lesion: the influence of various leukoreduction procedures on generation/retention of some biological response modifiers, microvesiculation, distribution of membrane-bound/soluble Prion and the rate of HLA-CLASS1 release. Trans Apher Sci, in press. This manuscript summarises strategy and progress both in the improvement of apheresis platelet quality and provision in NAIT.

Plateletpheresis: what's new?

1995 has brought several novelties into the field of thrombocytapheresis. The most important is the presentation by Baxter of the Amicus CFC apparatus that, in a two-vein collection time of 51-53 min, collects 3.93-4.13 x 10(11) platelets contaminated by 0.2 x 10(6) white blood cells (WBC) with an efficiency of 72-74%. Similar results are obtained in 55 min, in single-needle procedures, with a collection efficiency of 70.7%, a total yield of 4.3 x 10(11) and a contamination of 0.9 x 10(6) WBC. Presently the machine cannot collect red blood cells (RBC), along with platelets, as does the DFC Haemonetics MCS3p. With this machine in mandatory single-needle procedures lasting 80-85 min, approximately 4.5 x 10(11) platelets can be collected with a WBC contamination of 3.1 x 10(6). Along with the platelet cells (PC), with the SDP PRC protocol at the end of each pass it is possible to collect aliquots of plasma red blood cells (PRBC) (10-50 mL) with a haematocrit of 65%. Depending on the number of passes and on the donor's body weight (BW), from 1 and 2 U/PRBC containing approximately 55 g of haemoglobin (Hb) each can be obtained. This method not only costs less but also immunological and viral risks for the patients are more efficiently addressed since it is possible to reduce the number of allogeneic exposures in the same transfusion event. PRBC can also be collected with the Fresenius AS104 and the Dideco Excel apparatuses. Dideco is presently using the "Genova" separation chamber, which can collect an average of 4.8 x 10(11) platelets contaminated with 0.5 x 10(6) WBC, in approximately 55 min. The ACD-A-to-blood ratio may be as low as 1/20 since the very last belts and lines are coated with non-thrombogenic substances. Therefore, there is no alteration of the quality of the platelets as evaluated with monoclonal antibodies (MoAbs) anti-CD 62, 63, 36 and 51, no extra haemorrhagic risk for the donors and citrate reactions and microaggregate formation are totally eliminated. In 1995 there has also been some rejuvenation of the older cell separators. The CS3000+ uses the TN6/PLT 30 combination of separation collection chambers. Platelets are collected in only 30 mL of plasma, and non-plasma solutions containing acetate can be used for their resuspension. The Fresenius AS204 is ready for better-quality combined platelet collection, and RBC-PC collection with Cobe Spectra is under evaluation along with the leucocyte reduction system that apparently brings leucocyte contamination down to 0.35 x 10(5). This interest in thrombocytapheresis is also the result of the challenge that thrombopoietin phase I and II trials have promoted.

An overview of current trends in platelet preparation, storage and transfusion.

We present an overview of issues relating to preparation, storage and transfusion of platelet concentrates. The concepts of quality are described and potential benefits from leucodepletion, UVB irradiation and the use of additive solutions discussed. Emphasis is placed on laboratory evaluation of the storage lesion and in particular morphological changes of platelets during storage.

Automated processing of leucocyte-poor platelet concentrates.

In view of transfusion reactions and alloimmunization associated with leucocyte contamination of platelet concentrates (PC), there is a general move towards the production of leuco-poor PC. This goal is currently pursued by the production of various PC using buffy coat and apheresis techniques. Although there is no overall consensus on the meaning of 'leuco-poor', by assuming that this refers to a level of 5-50 x 10(7) leucocytes per PC, we were able to make comparisons with available systems used in Europe. In addition to platelet and white cell counts, other markers of PC quality were assessed in some cases. These included traditional markers (such as hypotonic stress response, pH, and lactate and beta-thromboglobulin levels) and newer markers (such as glycocalicin and plasma von Willebrand factor levels). Our preliminary results showed appreciable differences in platelet and white cell content of PC prepared by various types of apheresis equipment. Appreciable differences in the quality of stored PC were also observed between routine PC (non-leuco-poor and buffy coat and apheresed PC (leuco-poor).

The preparation of platelet concentrates by the light-spin/hard-spin technique.

For at least two decades the light-spin/hard-spin (LS/HS) method for preparation of platelet concentrates (PC) has been the standard of platelet support. With concern over the detrimental effects of platelet activation during component preparation and with increased recognition of the adverse consequences resulting from residual donor leukocytes in PC, new approaches to the production of PC have begun. This review addresses two aspects of the traditional LS/HS method of platelet preparation: platelet activation and residual leukocyte content. Studies of platelet activation are reviewed which focus on the second (hard-spin) centrifugation step during which pelleting of platelets occurs. Platelets studied immediately after the hard-spin exhibit evidence of alpha-granule release, expression of activation antigens, and decreased aggregation. There is a suggestion that some degree of reversal of platelet activation routinely occurs during the rest period following the hard-spin. The residual leukocyte content of PC prepared by the LS/HS method ranges from 10 7 to 10 9 leukocytes/unit. The residual donor leukocytes are predominantly lymphocytes and monocytes. Degeneration of residual donor leukocytes may release soluble cytokines resulting in febrile transfusion reactions. It remains controversial whether or not the cell-membrane fragments and microvesicles of degenerating donor leukocytes are capable of HLA allosensitization or viral transmission. Release of leukocyte elastase from degenerating leukocytes during platelet storage has been proposed as contributing to the platelet storage lesion. More research is needed to address the question of whether or not pre-storage leukocyte reduction during component preparation will result in improved PC. It appears likely that within the next few years radical changes will occur in the method of preparation of PC with the aim of providing the greatest degree of hemostatic effectiveness with the least toxicity to patients.

Trends in clinical hemapheresis 1986. Progress report on the 4th annual meeting of the European Society for Hemapheresis.

After a rather long initial period fraught with difficulties, plasma exchange has become an adjunct to the treatment of numerous diseases, such as hyperviscosity syndrome, where it alleviates disease symptoms, hemophilia due to inhibitors to clotting factor VIII, thrombotic thrombocytopenic purpura, rapidly progressing and Goodpasture glomerulonephritis, myasthenia gravis and Guillain Barré syndrome. In addition, plateletpheresis has also grown from being a procedure of experimental clinical application to one of practical routine importance; at the Berne University Hospital, approximately 25% of all transfused platelets in 1986 were apheresis platelets, a proportion that elsewhere may reach 40%. Despite the successes so far obtained with apheresis, many aspects of this therapy remain to be reconsidered. Improvement of donor-recipient matching and of yield in plateletpheresis, better selection of replacement fluids, and increased donor and patient safety and comfort may further strengthen the value of apheresis in therapeutic protocols. This was the major background for the scientific program of the 4th Annual Meeting of the European Society for Hemapheresis that was assembled to shed light on those aspects of the apheresis field which are still unclear. A total of 31 lectures and 76 individual contributions were debated by 280 participants from Europe and overseas. The present essay is a review of the highlights of this meeting, the main lectures of which were published in Plasma Therapy and Transfusion Technology, vol. 7, 1986.