Introduction

While direct measurements of the actual cholinesterase inhibitors and their metabolic byproducts in body fluids are very accurate, (Clark 2002) their usefulness is limited because

• Each test can only measure one chemical, so it is not useful if you do not know to which one the patient was exposed. (Schenker, Louie et al. 1998)
• The results are not available in time to assist in critical treatment decisions. (Mortensen 1986; Schenker, Louie et al. 1998; Clark 2002)
• Toxic levels for individual agents have not been established. (Erdman 2004)

However, when these test results are available, they can sometimes help in

• Assessing public health exposure risks to others.
• Providing forensic documentation of poisoning. (Wiener and Hoffman 2004)
• Documenting exposures as a cause of disability.

Note: if such tests are needed, state or federal public laboratories can be consulted.

Cholinesterase Inhibitors That Can Be Measured

Listed below are some of the cholinesterase inhibitors that can be measured in biological fluids.

• Sarin. (Abu-Qare and Abou-Donia 2002; Wiener and Hoffman 2004)
• Some organophosphorus pesticides.
• VX. (Wiener and Hoffman 2004)

Metabolic Byproducts That Can Be Measured

Alkyl phosphate and phenols (e.g., paranitrophenol (Durham and Hayes 1962)), which are byproducts of organophosphorus compounds

• Are sometimes used to quantitate exposure. (Mortensen 1986)
• Do not correlate with cholinesterase levels. (Namba 1971)
• May be detected for up to 48 hours in urine.
• May be positive before clinical signs appear or cholinesterase levels decrease). (Reigart and Roberts 1999)

Note: Excretion of OP compounds and metabolites is rapid while cholinesterase levels remain depressed for a longer period. (Karalliedde and Senanayake 1989)

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