Platelet additive solutions: a future perspective.

Platelet additive solutions (PASs) were first developed in the 1980s, and continued to be improved over the following years. The use of PASs as replacement for plasma has a number of benefits, both for the quality of the platelet concentrates and for the patients. However, some PASs have been associated with a lower platelet yield in the PCs, a shorter storage time, and a lower increment in the patient when compared to PCs in plasma. A number of reformulations of the PASs have taken place to counteract these disadvantages. Most PASs use acetate as nutrient for the platelets, which has the benefit of generating bicarbonate when oxidized by the platelets, thus supplying its own buffering capacity. Alternatively, glucose is used, but may cause deterioration of pH in the stored PCs due to the formation of lactic acid. Addition of other buffering substances, such as phosphate, can be added to ensure maintenance of neutral pH. An important finding was the inhibiting effect of potassium and magnesium on platelet activation. The initially developed PASs lacked these two ingredients and showed reduced storage times of the PCs in PAS when compared to those stored in plasma. However, when these constituents are included in the PAS, storage time is similar and even exceeds those seen for PCs in plasma. Considerable research is done in further formulating the optimal PAS. Bicarbonate is being considered as buffer for these PASs. Also, L-carnitine appears to have a favorable effect on stored platelets, including a reduction of platelet metabolism, and inhibition of apoptosis. Another area of optimization is lowering of plasma content needed for maintaining platelet quality. Where current PASs still need at least 30% residual plasma, there is a trend towards lowering the plasma content to less than 5% with the newer PASs. Preservation of purinergic platelet receptor functionality by ADP-degrading activities in plasma appears to play an important role in this respect. Development of PASs are usually based on in vitro studies alone. It is important to realize that only clinical studies can give definitive answers about the quality of platelets stored in PASs. Sofar, only limited clinical evaluations have been published that either studied the effectiveness of platelets in initially-developed PASs, or were specifically done in combination with pathogen reduction technologies. Thus, PASs seem to be an excellent replacement for (part of) the plasma when producing PCs, and allow extended storage with maintenance of quality, but more clinical studies are needed to substantiate in vitro results.