In Vivo Evaluation of Extended Stored Platelet Concentrates.

Background: With the introduction of bacterial testing, extended storage of platelets is now possible as long as platelet viability is maintained. Although apheresis platelets have recently been licensed for seven days of storage, platelet concentrates are still only licensed for five days. We performed studies to determine the post-storage viability of platelets stored as concentrates. As yet, there are no established criteria for platelet viability that must be met at the end of storage. However, two different criteria for evaluating post-storage platelet viability have been suggested:

1. compare the stored platelet results with each donor’s fresh platelet results; or

2. establish a fixed platelet standard with an expected mean value along with the lower limit of the 95% confidence interval (lower 95% CI) of the mean.

Methods: Forty-four normal volunteers donated a unit of whole blood, the whole blood was centrifuged to give platelet-rich plasma (PRP), and the PRP was then centrifuged to produce a platelet concentrate. The platelet concentrates were re-suspended and stored in either 100% plasma or in 20% plasma and 80% Plasmalyte (a platelet storage solution) for five to eight days in Terumo Teruflex bags. At the end of storage, a sample of blood was obtained from each volunteer to prepare fresh platelets to compare the results of a fresh platelet transfusion with the transfusion of the same volunteer’s stored platelets. The fresh and stored platelets were alternately radiolabeled with either ⁵¹Cr or ¹¹¹In, re-injected into their volunteer donor, and serial blood samples were drawn from the volunteer after transfusion of the fresh and stored platelets to determine platelet recoveries and survivals.

Results: Results are shown in Table 1.

Conclusions: After seven days of storage in plasma, the platelets could qualify for standards of:

1. 74% and 53% as a simple ratio of fresh to stored platelet recoveries and survivals, respectively;

2. according to Dumont’s method of analysis (Transfusion, in press), achievable stored platelet recoveries would be 63% of fresh and survivals would be 40% of fresh; and

3. as a fixed standard, platelet recoveries averaged 45% and survivals 4.4 days with lower 95% CI’s of 35% and 3.3 days, respectively.

After eight days of storage in plasma, platelet recoveries and survivals gave unacceptable results. Instead of increasing or at least maintaining post-storage platelet viability, Plasmalyte markedly reduced platelet viability compared to plasma stored platelets at each storage interval.