The effect of quick freezing on the preservation of selected serum enzyme activities.

Abstract

This study was undertaken to develop a technic for preserving the activities of serum glutamic oxalacetic transaminase, lactic acid dehydrogenase, and creatine phosphokinase in vitro . Fresh serum (4-ml. aliquots) was quickly frozen in a slush made of Dry Ice and acetone (temperature approximately –78 C ) , and then stored in an electric freezer (0 to –2 C ) . For comparison purposes, another group of serum samples was stored in a refrigerator at 4 C. The ultraviolet method with reduced diphosphopyridine nucleotide was used to measure the enzyme levels. Serum enzyme levels measured prior to quick freezing or cooling were compared with those after the serum had been frozen or cooled for 12, 24, and 48 hr. For all enzymes studied, there were no statistically significant differences ( p >0.10 in all cases) between the values measured prior to quick freezing and those measured 12, 24, and 48 hr. later. In direct contrast, statistically significant differences ( p ≥0.05 in all cases) were found between the enzyme levels of the precooled serum and the serum which had been refrigerated for 24 and 48 hr. If the quick freeze technic is utilized, selected days may be set aside in the laboratory for enzyme analysis, and samples collected over a 48-hr. period may be handled at this time.