Received on January 3, 2007
Accepted on April 17, 2007

General Clinical Chemistry

Intraindividual Stability of Human Erythrocyte Cholinesterase Activities

¹ US Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD, and Walter Reed Army Institute of Research, Silver Spring, MD
² US Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD
³ US Army Occupational Health Clinic, Bluegrass Army Depot, Richmond, KY

^* To whom correspondence should be addressed. E-mail: coleen.weese{at}us.army.mil.

Background: Erythrocyte cholinesterase (RBC-ChE) activities serve as useful and sensitive biomarkers to monitor exposure to cholinesterase-inhibiting substances, such as chemical warfare nerve agents and pesticides. Although the interindividual variation of RBC-ChE is well characterized, the magnitude of intraindividual variation for RBC-ChE remains controversial. An accurate measure of intraindividual variation is critical for establishing the appropriate frequency of RBC-ChE testing.

Methods: We retrospectively tracked the intraindividual variation of RBC-ChE activities among 46 male nerve agent workers from a single US Army depot that participated in a medical surveillance program requiring periodic RBC-ChE monitoring. All RBC-ChE analysis was performed by the same medical laboratory technician by the delta pH method.

Results: A mean of 38 and a median of 37 RBC-ChE measurements were available for each worker. The mean duration of employment for these workers was 20 years (median, 21 years). The mean CV for RBC-ChE in this set of 46 workers was 3.9%. Linear regression analysis of the data for each worker resulted in a mean slope of 0.0010 delta pH units/h per year.

Conclusions: RBC-ChE activities increased in each person by a mean of 0.01 delta pH units/h every 10 years, which is a negligible rate. These findings highlight the stability of RBC-ChE activities over time in a given individual and may have important policy implications regarding the appropriate frequency of RBC-ChE testing.