When to Test?
Cholinesterase-Inhibiting Pesticides
Test if working with Class one or Class two organophosphates (O Ps) or O Ps and N methyl carbamates for greater than a total of thirty hours in thirty consecutive days.
N Methyl Carbamates
If only working with N methyl carbamates, cholinesterase testing is not likely to be beneficial.
Baseline
Baseline Determination
Obtain baseline measures prior to working with cholinesterase inhibiting pesticides. When obtaining the baseline, ensure that cholinesterase inhibiting pesticide has not been handled in the immediate thirty days prior to testing.*
Second Baseline
A second baseline is recommended for improved precision but not essential. Wait to test at least three days after the baseline, but no longer than fourteen days (O E H H A, 2017). If a second baseline is obtained, average the two values. For accuracy, ensure no pesticide exposures during this time period.
Establish baselines annually.
Working Baseline
Working baselines (baselines that are established when a thirty day period free of O Ps exposure is not possible) are likely to increase false negatives. Perform a second baseline after halting exposure (the longest practicable exposure free period available is recommended, with a one week exposure free period at a minimum).
If values differ by more than ten percent, obtain a third baseline. The highest value should be used as the baseline.
Testing
Test Types
Measure both acetylcholinesterase (red blood cell cholinesterase; R B C C h E) and butyryl cholinesterase (plasma cholinesterase; Plasma C h E). Both R B C C h E and Plasma C h E tests are recommended. If only performing one test, do Plasma C h E.
Laboratory Services
Use the same laboratory and the same methodology for all testing so that results may be accurately compared.
Post Exposure Testing
Washington state recommends testing each time a worker exceeds or reaches thirty hours of exposure within any thirty day period after the baseline is established or after last post exposure test. California state recommends testing each time a worker exceeds or reaches six days of exposure within a sliding scale thirty day period.
Medical Removal
Remove worker from cholinesterase inhibiting pesticide exposure if their R B C C h E is less than seventy percent, and or their Plasma C h E is less than sixty percent of the baseline.
Level to Return to Handling
Return to Handling
Return to handling when R B C C h E and Plasma C h E are both greater than or equal to eighty percent of baseline.
Retest for Return to Work
Days to repeat test is determined by degree of reduction in cholinesterase activity or may consider testing weekly.
For R B C C h E: calculate percent depression minus 20, then divide by zero point eight three. The resulting number equals number of days to repeat test.
For Plasma C h E: calculate percent depression minus 20, then divide by one point two. The resulting number equals number of days to repeat test.
Review of Handling Practices
Review pesticide handling practices when test results are less than eighty percent of baseline.
Cholinesterase Testing Protocol Algorithm
[Decision tree format. Answers to each question point you to the next question to consider.]
- Will the worker handle O Ps or O Ps and N methyl carbamates for thirty hours or more in thirty consecutive days (this is the Washington (W A) state recommendation. California (C A) state recommends follow up testing if worker reaches six days of exposure within a sliding thirty day schedule. At this time, W A and C A are the only states with formal cholinesterase monitoring programs with regard to pesticide exposure. Days of exposure are easier to track than hours of exposure)? If no, stop. If yes, move to question two.
- Was there exposure within the past thirty days? If no, test to obtain at least one baseline, and move to question three. If yes, obtain a working baseline. Take one test, then wait at least three days to take another test. Use the highest result as the working baseline, and move to question three.
- Did the worker exceed or reach thirty hours of exposure within thirty days since the baseline or follow up test (this is the Washington (W A) state recommendation. California (C A) state recommends follow up testing if worker reaches six days of exposure within a sliding thirty day schedule. At this time, W A and C A are the only states with formal cholinesterase monitoring programs with regard to pesticide exposure. Days of exposure are easier to track than hours of exposure)? If no, stop. No testing required. If yes, within one week, conduct follow up test, to monitor, and move to question four.
- Is the R B C C h E and or Plasma C h E greater than or equal to eighty percent of the baseline? If yes, loop back to question three. If no, retest (strongly recommended but not mandatory), review pesticide handling practices, and move to question five.
- Is the R B C C h E less than seventy percent, and or the Plasma C h E less than sixty percent of the baseline? If no, loop back to question three. If yes, remove the worker from workplace pesticide exposure and repeat testing at scheduled intervals (see following) to follow recuperation, and move to question six. For R B C C h E: Calculate percent depression minus twenty. Divide the result by zero point eight three. This equals the number of days to repeat test. For Plasma C h E: Calculate percent depression minus twenty. Divide the result by one point two. This equals the number of days to repeat test.
- Is the R B C C h E and or Plasma C h E greater than or equal to eighty percent of the baseline? If no, loop back to question five’s yes response of repeating testing at scheduled intervals to follow recuperation. If yes, worker can return to handling O Ps or O Ps and N methyl carbamates. Then loop back to question three.
Threshold exposure level
When the worker exceeds or reaches thirty hours of exposure in a thirty day period.
- O Ps: Class one or Class two organophosphates.
- R B C C h E: Acetylcholinesterase, also known as red blood cell cholinesterase.
- Plasma C h E: Butyryl cholinesterase, also known as plasma cholinesterase.
Notes
- Obtain baseline prior to pesticide work or after thirty days of worker being exposure free.
- When testing, it is recommended to get both R B C C h E and Plasma C h E. But if only performing one test, then do Plasma C h E.
- A second baseline is recommended for improved precision but not essential.
- N methyl carbamates do inhibit cholinesterase, but the cholinesterase reactivates quickly, making testing unreliable in predicating overexposure.
[The Fine Print]
Acknowledgements
National Farm Medicine Center, AgriSafe Network, and Migrant Clinicians Network. Matthew Keifer, M D, M P H and Carolyn Sheridan, R N, B S N served as the lead authors with support from Amy K. Liebman, M P A, M A.
Revised on February 16, 2023 by Steven Kirkhorn, M D, M P H and Matthew Keifer, M D, M P H, National Farm Medicine Center external scientific advisor.
Resources
Brown, A., Miller, M., and Keifer, M. (2013). Number Thirty: Cholinesterase monitoring: A guide for the health professional. Pesticide information leaflet. University of Maryland Extension. pesticide.umd.edu/uploads/1/3/5/6/13565116/pil30_che-hcps_1999-2013.pdf.
Furman, J. (2010). Cholinesterase monitoring for agricultural pesticide handlers: Guidelines for health care providers in Washington state. Washington State Department of Labor and Industries: Division of Occupational Safety and Health. lni.wa.gov/ safety-health/docs/Providers Guidelines 1.pdf.
The Office of Environmental Health Hazard Assessment. (2017). Guidelines for physicians who supervise workers exposed to cholinesterase inhibiting pesticides (sixth edition). California Environmental Protection Agency. oehha.ca.gov/ pesticides/california-medical-supervision-program.
Roberts, J. and Routt Reigart, J. (2013). Recognition and management of pesticide poisonings (sixth edition). U. S. Environmental Protection Agency: Office of Pesticide Programs. epa.gov/sites/default/ files/2015- 01/documents/rmpp_6thed_final lowresopt.pdf.
Disclaimer
This material was produced, in part, under Assistance Agreement Number X 8 8 3 4 8 7 6 0 1 awarded by the U. S. Environmental Protection Agency. It has not been formally reviewed by E P A. E P A does not endorse any products or commercial services mentioned in this product. This material was produced, in part, under grant S H 2 2 2 8 4 1 1 6 0 F 19 from the Occupational Safety and Health Administration, U. S. Department of Labor. It does not necessarily reflect the views or policies of the U. S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U. S. Government. The project described was supported by Grant Number U 3 0 C S 0 9 7 4 2 from Health Resources and Services Administration. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Health Resources and Services Administration.
Logos and Developed By
- AgriSafe Network, Protecting the People Who Feed the World.
- MCN, Migrant Clinicians Network.
- National Farm Medicine Center.
- Ag Health and Safety Alliance