Background: The maximum storage period of platelet concentrates at room
temperature using usual method is 5 days. And so, long-term storage of platelet
concentrates for the emergency transfusion and autotransfusion is very difficult. For
solving this problem, it is essential to create the method for long-term storage of
platelet concentrates. Platelet cryopreservation is known as the most suitable method for
long-term storage. And so, we tried to analyze the status of frozen thawed platelet
concentraces for the evaluation of practical applicability.
Methods : The apheresis platelet concentrates were transfered to PL-732(Baxter, USA)
cryopreservation bag, and 99% DMSO(Sigma, USA) was added to those bags at slow
rate until 6% concentration is achieved. Thereafter, those were directly placed to -80℃
refrigerator for storage. Somedays later from 7 to 43 days, those were thawed at 37℃
water bath and washed by the same volume of ABO matched plasma. Total 10 units of
platelet concentrates were evaluated for platelet recovery rate, LDH, pH, bacterial culture
and aggregation test with collagen and ristocetin for the comparison of pre-freezing and
post-thawing state. Among these, 7 units of platelet concentrates were transfused.
Three cases were autotransfusion and 4 cases were allotransfusion. The transfusion
effect was evaluated with corrected count increment(CCI) and bleeding time(BT)
recovery.
Results :
1) The mean platelet recovery rate was 93%.
2) The LDH level was increased significantly at post-thawing state to that of
pre-freezing state(P<0.05), but the mean level(269 IU/L) was in the clinical acceptable
range and the pH level showed no significant difference between pre-freezing and
post-thawing state.
3) In bacterial culture, no growth of bacteria was found at any platelet concentrates.
4) The platelet aggregation to collagen and ristocetin was significantly lower in
post-thawing state than pre-freezing state(P<0.05).
5) The mean storage periods of platelet concentrates at -80℃ refrigerator were 27
days and the mean CCI was 9,700/μL with no adverse reactions. One case of ITP with
prolonged BT more than 10 minutes showed improved BT of 3 minutes 30 seconds after
1 hour after platelet transfusion.
Conclusion: It could be suggested that the method of platelet preservation using 6%
DMSO and -80℃ storage was practically applicable.

Keywords: Platelet concentrate, DMSO, -80℃ Storage