Determination of blood cholinesterase activity is a valuable indicator of exposure to carbamate and organophosphorus pesticides. The activity can be measured before and after application of these pesticides. The results indicate the extent of exposure and hence provide the basis for advice on measures to be taken, particularly in the case of highly depressed activity levels. For biomonitoring purposes, determination of both erythrocyte acetylcholinesterase and plasma butyrylcholinesterase activity is recommended. In this study, reference values for plasma and erythrocyte cholinesterase activities were determined on apparently healthy Costa Rican females, males and children of both sexes, without occupational exposure to known cholinesterase-inhibitors. Kinetics methods based on Ellman's colorimetric technique were used. Plasma cholinesterase activity ranged from 3 700 to 9 700 U/L in females (17 to 75 years, n = 139); from 4 500 to 9 900 U/L in males (17 and 75 years, n = 134), in girls (6 to 13 years, n = 50) ranged from 3 820 to 9 100 UI/L and in boys (6 to 13 years, n = 50) ranged from 4 660 to 9 160 UI/L. Erythrocyte cholinesterase activity corrected for hemoglobin in females, males, girls and boys ranged (95% percentile range) from 26,1 to 40,9 UI/g Hb; 26,2 to 41,8 UI/g Hb; 24,6 at 37,7 UI/g Hb and 25,9 to 39,3 UI/g Hb, respectively. The use of these reference values for the costarrican population is recommended.

plasma cholinesterase; erythrocyte cholinesterase; reference values; plaguicides; organophosphates; carbamates