Time-dependent effects of storage at –80 °C on the stability of butyrylcholinesterase activity in human serum

Objectives: Butyrylcholinesterase (BChE) is an important biomarker in serum, and aberrant BChE activity indicates onset and progression of human diseases. The duration of serum storage at −80 °C may introduce variability into and compromise the reproducibility of BChE activity measurements. Design and Methods: We collected serum samples from eight healthy volunteers and determined serum BChE activity in these samples using a sensitive fluorescence assay at various time points during a six-month storage period at −80 °C. Changes in averaged BChE activity over storage time were assessed by repeated measures analysis of variance (ANOVA). Sidak multiple comparisons test was also used to perform post-hoc analysis. Results: Almost all determined BChE activity values lay within the normal physiological range of BChE activity. However, repeated measures ANOVA using mean BChE activity vs. storage time showed that BChE activity values from two time points were significantly different. Analysis by Sidak multiple comparisons test provided no substantial change of BChE activity during the first 90 days of storage, but BChE activity noticeably decreased after 90 days. Conclusions: Serum samples stored in −80 °C for up to 90 days can be exploited to accurately determine BChE activity.