Cholinesterase Testing Procedures

April, 2022

Dear Stakeholders:

You are receiving this message because you are part of the agricultural community, or are a health care provider involved with cholinesterase testing associated with the application of organophosphate or N-methyl-carbamate pesticides in Washington State.

As part of the Washington State Department of Labor & Industries (L&I), the Division of Occupational Safety and Health (DOSH) is the state regulator of worker safety and health. DOSH enforces the cholinesterase monitoring requirements of WAC 296-307-148, which protects agricultural pesticide handlers who apply organophosphate and carbamate pesticides, ensuring those chemicals are used safely at work. As part of administering these regulations, L&I approves laboratories that analyze serum (butyryl) and red-blood cell (RBC) (acetyl) cholinesterase samples.

Currently, in the state of Washington, the only laboratory approved to conduct these tests to meet the obligations of the cholinesterase monitoring rule is LabCorp. LabCorp has informed DOSH that they are not currently able to carry out RBC acetylcholinesterase testing because their supplier of the acetylcholinesterase reagent necessary to perform the test has stopped making the required product.

At this point, serum (butyryl) cholinesterase testing must continue, as described by the rule, including getting baseline levels and follow-up samples for those who are conducting spraying activities within the scope of the regulation. When ordering the test, the instruction from LabCorp is to use a new profile with only the serum test (see below).

New profile 123029 WA Pesticide Monitoring Prof. was created, which includes 007211 Cholinesterase, Serum and 123003 CHE, Serum.

This profile will be used instead of 123008 WA Pesticide Monitoring Prof. that was made non-orderable on March 21, 2022, due to 007286 Cholinesterase, RBC being discontinued.

To get further information on the protocol, please contact:

Darrin Schmidt at LabCorp

LabCorp is working on identifying a new source of test materials to resume providing RBC acetylcholinesterase testing for occupational surveillance in Washington. At the same time, DOSH is examining options for addressing the lack of availability of RBC acetylcholinesterase testing. As additional options become available, DOSH will provide guidance on resuming RBC testing.

We have been made aware that some employers may have been advised to use other labs in order to get RBC acetylcholinesterase testing. If so, be aware that all follow up testing for those workers must be done through the other lab. Cholinesterase results from different labs may not be comparable. Our understanding is that these other labs likely will not be able to continue with the testing through the growing season.

During the period RBC acetylcholinesterase testing cannot be obtained from any Washington-State-approved laboratories, employers will not be cited for their inability to make RBC acetylcholinesterase testing available per WAC 296-307-148.

If you have any questions or feedback regarding this communication, please contact Dr. Nicholas Reul (