title: Intraindividual stability of human erythrocyte cholinesterase activity.
abstract: 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.
authors.affiliation: US Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD 21010-5403, USA.
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Lefkowitz
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Kupina
authors.forename: Nigel L
authors.initials: NL
authors.lastname: Hirth
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Henry
authors.forename: Georgia Y
authors.initials: GY
authors.lastname: Noland
authors.forename: John Y
authors.initials: JY
authors.lastname: Barbee
authors.forename: Joey Y
authors.initials: JY
authors.lastname: Zhou
authors.forename: Coleen B
authors.initials: CB
authors.lastname: Weese
mesh_terms: D015415:Biomarkers / Q000097:blood; D002617:Chemical Industry; D002800:Cholinesterase Inhibitors / Q000009:adverse effects; D002802:Cholinesterases / Q000097:blood*; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D016014:Linear Models; D008297:Male; D016273:Occupational Exposure / Q000009:adverse effects; D009943:Organophosphorus Compounds / Q000009:adverse effects; D012016:Reference Values; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D015415:Biomarkers; D002800:Cholinesterase Inhibitors; D009943:Organophosphorus Compounds; D002802:Cholinesterases