CREATINE-KINASE ACTIVITY DECREASE WITH SHORT-TERM FREEZING

Freezing of serum samples at -30 degrees C without protective agents i s the simplest and least expensive method of storage in serum banks. W e investigated the stability of creatine kinase (CK) in human sera aft er freezer storage under such conditions for 24 h (n = 30) or for 2 or 4 weeks (n = 99). CK activity was measured in fresh sera and compared to matched thawed sera after freezer storage at the designated time i ntervals. The enzyme's median activity decreased significantly after 2 4 h, 2 weeks, and 4 weeks of freezer storage by 2.6, 5.9, and 8.3 %, r espectively (p < 0.0001, r = 0.99). Sex or high CK initial values had no significant effect on these results. We conclude that freezer stora ge of serum at -30 degrees C, even for short periods, causes a steady and significant decline in CK activity. These results should be taken into consideration when analyzing CK activity in frozen sera for resea rch or clinical purposes.