Protective effect of glycerol against the increase in alkaline phosphatase activity of lyophilized quality-control serum.

We studied the effectiveness of glycerol or ethylene glycol in preventing the increase in alkaline phosphatase activity of lyophilized or refrigerated quality-control serum after reconstitution or repeated freezing and thawing. Control serum reconstituted completely from the lyophilized state with subsequent storage at -20 degrees C showed a considerable decrease in alkaline phosphatase activity immediately after thawing, and a gradual increase in activity on allowing it to stand at room temperature. Adding glycerol or ethylene glycol to the reconstituted serum obviated these changes in activity, glycerol being more effective than ethylene glycol. Reconstituted serum with added glycerol maintained maximum activity before refrigeration during either storage for 30 days or on repeated freezing and thawing. Practical applications of this glycerol-supplemented control serum are discussed.