Objective     To explore potential shelf-life of cryo-platelets by evaluating pivotal elements to platelet injury.      Methods     The ability of platelets cryopreserved at deep low temperature for one to six years to express CD62p and re-express after ADP induction was detected with flow cytometry.      Results     When the platelets preserved at -80 ℃ for the first 12 to 48 months

CD62p expression on the platelets was well restrained and of no significant difference with the liquid platelets stored at room temperature for 28 h

while CD62p re-expression induced by ADP was effectively maintained

and the positive rate of re-expressed CD62p [(70.2±10.3)%] as the platelets preserved at -80 ℃ for 36 h was not significantly different with that [(70.4±21.5)%] of the liquid platelets stored at room temperature for 24 h (P0.05). However

the positive rate of re-expressed CD62p declined to (35.2±18.2)% when the platelets stored at -80 ℃ for 48 months

with significant difference with that for 36 months (P0.01). As control

when the liquid platelets held at 22 ℃

the positive rate of CD62p was (2.2±1.5)% in 1 h after collection

then promptly increased

showed significant difference with that at 24 h (P0.05)

at 48 h

at 72 h (both P0.01). As for re-expressed CD62p

the positive rate was (83.5±14.7)% in 1 h

then rapidly decreased

with significantly difference with that at 48 h (P0.01).      Conclusion     The key factor to the quality of cryo-platelets is the metabolic injury of the liquid platelets occurred at the stand-by period before cryopreservation. Therefore

if cryopreserved in 24 h after collection

platelets could be preserved for at least three years at -80 ℃.