Stability of Values for the Activities of Critical Enzymes Assayed in Serum Frozen for Prolonged Time Periods

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Abstract.Objectives. Our medical center laboratory receives frozen clinical chemistry samples from outlying hospitals for which assays for critical enzyme activities are requested. Our objective is to determine the effects of freezing (-20°C) on these enzyme activities in samples over a one month period. Methods. Enzyme activities for ALP, AST, ALT, CK and LD for 30 patient's sera were stored at-20°C and were assayed on a Beckman-Coulter AU5800 analyzer at 0, 15 and 30 days after collection. Statistical tests were performed to determine if the values were statistically the same or different. Results. F-tests for all five enzyme levels showed no statistically significant differences (p>>0.05); linear regression analysis showed high correlation of results (r>0.99 for all correlations) with some bias for ALT. Conclusions. We conclude that the activities of these enzymes are stable, except possibly ALT, when stored frozen at -20°C over the 15- and 30-day storage periods.

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