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Quality of Fresh‐Frozen Plasma during Storage

Fresh-frozen plasma (FFP) either prepared from whole blood or collected by plasmapheresis plays an important role in the treatment of coagulation disorders. Normal storage conditions for FFP involve temperatures varying between –30 C for 1 year and –40 C or below for 2 years as an accepted standard, by which the quality of plasma proteins shows no deterioration [1–4]. In order to reduce transfusiontransmitted virus infections, in Germany FFPs are stored in quarantine and are released for transfusion only if the serological viral parameters (anti-HIV 1,2, HBsAg, anti-HCV) of the pertinent donor are negative at a second examination 6 months after the donation [3]. This results in limited permitted storage times of FFPs. Therefore, we prospectively examined the effects of an extended storage period at –30 C for up to 2 years in 90 FFPs, which were frozen within 6 h after blood donation and consecutive separation into components. For sampling purposes, each unit was thawed after 15, 18, 21 and 24 months and refrozen immediately. The content of total protein, protein C, protein S, antithrombin III, fibrinogen and the coagulation factors II, V, VII, VIII, IX, X, XI and XII were investigated. Coagulation factors were determined by one-stage assays and were calibrated using commercial plasma standards, which had been calibrated against the respective WHO preparations, when available. Results are expressed as percentages where 100% corresponds to 1 U/ml. At the end of storage (24 months) we found only slight differences in most of the parameters investigated in comparison with the values after 18 or 21 months (table 1). In addition, the repeat thawing/freezing procedures in order to obtain samples for testing were possibly responsible for reduced concentrations of coagulation factors II, VII and VIII:c at the end of storage, but with the exception of factor VII, these differences were moderate. Moreover, contaminating cells in plasma may have a negative influence on labile coagulation factors [5, 6]. In a previous study, storage of FFP for 12 months at –30 C resulted in no deleterious effect on factor VIII [7]. In our studies, however, factor VIII:c, which is accepted as the most sensitive coagulation factor to control the quality of plasma, had adequate values at the end of the extended storage, which met the demands of the Council of Europe ( 70% of the original factor VIII) for FFP [1]. Alternatives to quarantine storage combined with donor retesting are virus inactivation procedures used to obtain plasma as safe as possible concerning the risk of virus transmission. Currently used virus inactivation procedures, i.e. solvent/detergent treatment or methylene blue photoinactivation, also result in loss of plasma proteins [8]. Most of the coagulation parameters investigated in our study had similar or higher values when compared with solvent/detergent-treated plasma pools [9]. In spite of several thawing/freezing procedures and a storage temperature of only –30 C, sufficient amounts of plasma proteins were observed after 24 months. From our data, storage time of FFP at –30 C can be extended to this duration, thus facilitating the quarantining of FFP.