The Viability of Stored Human Platelets

Viability of normal human platelets preserved for short intervals at 4 C. was studied by in vitro labelling with Na₂Cr⁵¹O₄. As a criterion of viability two parameters were used: (1) the survival time of the infused platelets, and (2) the maximum percentage of platelet radioactivity which could be recovered in the circulation after infusion. From these two parameters the platelet viability index was calculated, and for stored platelets this was expressed in per cent of the value obtained with freshly prepared platelets.

After 3 hours of storage at 4 C. the platelet viability index was reduced to 62 per cent. With longer periods of storage the viability of the platelets fell rapidly with viability indices of 12 per cent after 24 hours and 2 per cent after 48 hours. No significant difference was seen whether the platelets were stored as whole blood, as platelet-rich plasma, or as platelet concentrates suspended in a plasma medium. When stored in saline the platelets lost their viability more rapidly and the viability index was less than 5 per cent after only 24 hours. When the platelets were stored for 24 hours in a DAS-gelatin medium, their viability fell to insignificant levels within 24 hours.

Platelets frozen in glycerol-plasma and stored for 24 hours at —75 C. showed reduction of viability to one-fifth the value obtained with fresh, unfrozen platelets. Even without storage the frozen platelets showed similar values of viability.

From these results the following conclusions may be drawn:

1. Conventional methods of storage at 4 C. result in rapid loss of platelet viability. An inverse, almost logarithmic, relationship exists between time of storage at 4 C. and platelet viability. The glycerol-freezing technique, although better than most available methods, induces a great loss in platelet viability.

2. At present no method can be advised by which platelets can be preserved in viable form even for relatively short periods of time. However, it is important to know that in the absence of plasma, platelet viability is lost more rapidly than in a plasma medium.

3. From the data obtained, it seems advisable for the practice of platelet transfusion to infuse platelets within less than 3 hours after collection.

4. Methods of improving the viability of stored blood platelets based upon their metabolic needs are strongly warranted and are now under study.