Cholinesterase - Provider Information

Information for Medical Providers

Background and purpose

The Cholinesterase Monitoring rule (WAC 296-307-148 (7.11 MB PDF)) requires agricultural employers to provide medical monitoring for workers who handle toxicity Category I or II organophosphate or N-methyl-carbamate cholinesterase-inhibiting pesticides. The rule has been amended to reflect current program requirements, including requiring the employer to obtain a written recommendation from the health care provider for each employee test (incl. baselines) and evaluation and ensuring that the employee receives a copy. The updated rule became effective Feb. 1, 2006.

Medical monitoring provides several benefits. It provides the primary benefit of preventing over-exposure to cholinesterase-inhibiting pesticides before illness occurs. In addition, it increases employer and worker awareness of pesticide hazards and reinforces appropriate work practices. If blood testing detects cholinesterase depression, the employer is directed by the medical provider to evaluate the worker's pesticide handling practices. If cholinesterase levels fall below specified removal levels, medical monitoring facilitates case management and the employer is directed by the medical provider to remove the worker from further exposure until cholinesterase levels regenerate and it is safe for the worker to return to working with cholinesterase-inhibiting pesticides.

Medical monitoring

Medical monitoring is a surveillance program that monitors agricultural workers who handle toxicity Category I or II organophosphate or N-methyl carbamate pesticides. It consists of periodic measurements of cholinesterase activity levels in workers that are compared to measurements of exposure-free baseline cholinesterase activity levels. Workers who handle cholinesterase-inhibiting pesticides for 30 or more hours in any consecutive 30-day period are covered by the medical monitoring requirements of the rule.

L&I along with the Department of Health, University of Washington Department of Environmental Health and the Pacific Northwest Agricultural Safety & Health Center (PNASH) has produced a clinical manual titled: Cholinesterase Testing: Guidelines for Health Care Providers (576 KB PDF), which explains and interprets the state program of cholinesterase monitoring.

Laboratory testing

There is significant variation among cholinesterase testing methods and among laboratories using the same testing method; it is misleading to compare test results from one method to another or from one laboratory to another. Because of this, a laboratory approved by L&I must be used for all cholinesterase tests. The only laboratory approved by L&I to provide cholinesterase testing under WAC 296-307-148 is Pathology Associates Medical Laboratories (



Referral list

As a service to medical providers and employers, L&I is publishing a list of medical providers that are offering cholinesterase monitoring services. Please contact John Stebbins (206-515-2870 or be included in this listing.

Contact information

For questions about the cholinesterase monitoring rule and other program issues contact John Stebbins (206-515-2870 or

End of main content, page footer follows.

Access Washington official state portal

   © Washington State Dept. of Labor & Industries. Use of this site is subject to the laws of the state of Washington.

Help us improve