title: [Correlation and conversion of plasma cholinesterase activity values using three techniques].
abstract: OBJECTIVE
  To determine mathematical correlations of three quantitative techniques to measure plasma cholinesterase, using reference values already established for two populations in the department of Antioquia, Colombia.
  
  
  METHODS
  In this descriptive, cross-sectional, prospective study, two independent, representative samples of working adults (18 to 65 years old) were examined. In both samples the adults worked for businesses associated with Colombia's Social Security system. Adults in the two samples had not been exposed to cholinesterase-inhibiting pesticides. The samples were from two neighboring regions of the department of Antioquia: one sample (415 adults) was from the Aburrá Valley, and the other (412 adults) was from Oriente Antioqueño (Eastern Antioquia). Plasma cholinesterase (EC 3.1.1.8) was measured using three quantitative methods: Michel, EQM, and Monotest. Linear regression equations were developed to correlate results of these three techniques.
  
  
  RESULTS
  Six simple linear regression equations were defined to show the relationship of three measurement techniques for plasma cholinesterase. There was a moderate correlation of the three techniques (r = 0.686 to 0.771), but it increased (r = 0.744 to 0.811) when 12 (1.5%) outliers were eliminated. Associations among the three techniques were highly significant (P < 0.001). The adjusted equations for Y = a + bX are: EQM (U/mL) = 0.40773 + 1.8757 (Michel [delta pH/h]); Michel (delta pH/h) = 0.25799 + 0.33871 (EQM [U/mL]); Monotest (U/L) = 462.0 + 4 565.0 (Michel [delta pH/h]); Michel (delta pH/h) = 0.42956 + 0.00012125 (Monotest [U/L]); EQM (U/mL) = 0.75333 + 0.00031056 (Monotest [U/L]); and Monotest (U/L) = 262.0 + 2 118.0 (EQM [U/mL]).
  
  
  CONCLUSIONS
  The proposed mathematical models allow conversion of cholinesterase activity values using the Michel, EQM, and Monotest techniques. These models can be of assistance in Colombia and other countries where a variety of measurement techniques are used, and where it becomes difficult to compare the results of different studies. Having mathematical models available for conversion of established values can be beneficial whether for clinical or epidemiological purposes.
authors.affiliation: Facultad de Medicina, Grupo de Malaria, Universidad de Antioquia, Calle 62 No. 52-59, Laboratorio 610, Medellín, Colombia. jaimecarmonaf@hotmail.com
authors.forename: Jaime
authors.initials: J
authors.lastname: Carmona-Fonseca
mesh_terms: D000293:Adolescent; D000328:Adult; D002091:Butyrylcholinesterase / Q000097:blood; D002802:Cholinesterases / Q000097:blood*; D003124:Colorimetry / Q000379:methods*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011199:Potentiometry / Q000379:methods*; D011446:Prospective Studies; D012016:Reference Values; D013053:Spectrophotometry / Q000379:methods*
chemical_list: D002091:Butyrylcholinesterase; D002802:Cholinesterases