Cholinesterase Monitoring


What are employers required to do?

The rule requires employers of agricultural pesticide handlers who use toxicity class I or II organophosphate or N-methyl-carbamate pesticides to take the following steps:

  • Record the number of hours employees spend handling these pesticides.
  • Implement a medical monitoring program for workers who could meet or exceed the handling threshold of 30 or more hours in any consecutive 30-day period.
  • Identify a medical provider to provide medical monitoring services.
  • Make baseline and periodic cholinesterase testing available to employees who could meet or exceed the handling threshold.
  • Investigate work practices when a handler's red blood cell (RBC) or serum cholinesterase level drops more than 20 percent below the employee's personal baseline.
  • Remove employees from handling and other exposures to organophosphate and N-methyl-carbamate pesticides when recommended by your health care provider.
  • Provide training on cholinesterase monitoring to covered employees.
  • Report employee handling hours to the medical provider with each periodic test.
  • Maintain medical monitoring and other records for seven years.

Employer cost reimbursement

Employers may request reimbursement for the reasonable costs of training, recordkeeping, and medical expenses for cholinesterase monitoring by submitting the Cholinesterase Monitoring Reimbursement Request form along with required documentation.


What is cholinesterase?

Cholinesterase (acetyl cholinesterase) is an enzyme that removes the chemical neurotransmitter acetylcholine from the junctions between nerves cells. Cholinesterase serves as the nervous system's "off switch" and is essential to the normal function of the nervous system.

Why monitor cholinesterase levels?

Exposure to organophosphate or N-methyl-carbamate pesticides may lower the level of available cholinesterase. Without the normal protective levels of cholinesterase, nerves in the body may be overstimulated to the point of exhaustion, leading to symptoms ranging from blurred vision, diarrhea and tremors to seizures, loss of consciousness and even death.

Monitoring cholinesterase levels in the blood through simple laboratory tests can detect cholinesterase depression prior to the onset of illness. When significant cholinesterase depression is identified employers are required to evaluate their pesticide worker protection program and make corrections to prevent further over-exposure.

What are the benefits of cholinesterase monitoring?

The cholinesterase monitoring Cost Benefit Determination and Small Business Impact Statement identified the following benefits of cholinesterase monitoring:

  • Prevention of illness after over-exposure.
  • Increase hazard awareness and improve overall workplace safety related to pesticide use.
  • Improve pesticide illness diagnosis and reporting.
  • Provide greater certianty about frequency of pesticide over-exposure.
  • Decrease the risk of unintended exposures to workers families.

Additional resources

How can I get help from L&I?

The L&I office in your area has industrial hygienists who can assist with specific questions. Please call your local area L&I office and ask for a consultation supervisor.

Region 1: 425-290-1300

Island, San Juan, Skagit, Snohomish, and Whatcom counties.

Region 5: 509-454-3700 or 1-800-354-5423

Adams—west side, Asotin, Benton, Chelan, Columbia, Douglas, Franklin, Grant, Kittitas, Okanogan, Walla Walla and Yakima counties.

More help from L&I

For general information, call 1-800-423-7233.

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