Cholinesterase enzyme activity in human blood samples: effects of the store conditions

Abstract

Introduction: Determination of cholinesterase (ChE) enzyme activity is the main biomarker of exposure to pesticides organophosphorus and carbamate. Therefore, the enzyme stability of ChEsin blood samples is an important pre-analytical factor to take into account in the diagnosis. Objective: To determine the effect of storage time and temperature on ChEs enzyme activity in human blood samples. Methodology: Whole-blood samples and erythrocyte suspensions (erythrocyte + 0.9% saline solution; ratio 1:1) were stored at -20°C, 4°C and 25°C. Enzyme activity measurements were performed at one hour after the blood samples have been obtained and then were repeated between days 1 and 90. Total ChE and Acetyl-ChE activities were determined using the Limperos & Ranta colorimetric method and the potentiometric method of Michel respectively. Results: The maximum stability of the total ChE enzyme activity was achieved at -20°C for 60 days and, in the case of Acetyl-ChE, at 4°C for the time the study was conducted. A decrease of Acetyl-ChE activity was shown after 7 days at 25°C and 4 days at -20°C. Conclusion: In terms of diagnosis, we recommend that in order to measure the total ChE activity the wholeblood samples should be stored at -20°C for 30 days, whereas to measure the Acetyl-ChE activity the erythrocyte suspensions in 0.9% NaCl at 4°C for 14 days.