Rationale:

• Blood cholinesterase activity levels are surrogate markers for the tissue cholinesterase activity level, which cannot be measured.
• Activity level does not, however, directly correlate with the presence of symptoms.
• Cholinesterase activity levels rarely will be available rapidly enough to aid in the acute management of the patient but may be helpful for purposes of confirming the diagnosis and follow-up; the test is most useful when a preexposure baseline cholinesterase activity level is known.

Evidence:

• After vapor exposure, early symptoms are due to local effect and no correlation with measured cholinesterase activity is noted. Sarin and VX seem to preferentially inhibit erythrocyte cholinesterase over plasma cholinesterase (18).
• In a case series of patients exposed to sarin vapor, miosis was a more sensitive index of exposure than the erythrocyte cholinesterase activity level (19).

Comments:

• None.