Cholinesterase Inhibition Thresholds and Neurobehavioral Impairment in Agricultural Workers Exposed to Organophosphate Pesticides

Abstract Objective To evaluate whether the cholinesterase inhibition thresholds identify neurobehavioral impairment during the spraying season among agricultural workers occupationally exposed to organophosphate pesticides. Methods We analyzed erythrocyte acetylcholinesterase (AChE) and plasma butyrylcholinesterase (BChE) activities in 78 agricultural workers before and during the spraying season. Neurobehavioral performance was assessed using a multidomain test battery, and global neurobehavioral impairment was defined using a predefined algorithm. Sensitivity, specificity, predictive values, and receiver operating characteristic (ROC) curves were used to evaluate the classification performance of predefined cholinesterase inhibition thresholds. Results The prevalence of global neurobehavioral impairment increased from 22% before spraying to 31% during the spraying season. The current 30% threshold showed low sensitivity for detecting impairment (29.2% for AChE; 8.3% for BChE). Lowering the inhibition threshold produced only modest gains in AChE sensitivity (33.3% at 20% and 37.5% at 10%) and larger gains for BChE, but these were accompanied by progressive reductions in specificity. ROC analysis showed limited discriminative capacity for continuous relative activity-change values (AUC: 0.56 for AChE; 0.46 for BChE). Conclusions The current 30% cholinesterase inhibition threshold showed low sensitivity for identifying neurobehavioral impairment in this sample of agricultural workers. Lowering the predefined inhibition threshold did not provide a threshold with both adequate sensitivity and specificity, consistent with the poor discrimination observed in ROC analysis. These findings suggest that adjustment of the cholinesterase inhibition threshold alone may be insufficient for identifying neurobehavioral impairment in occupational surveillance.