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Tests for the enzymes acetylcholinesterase (also known as RBC cholinesterase) and pseudocholinesterase (also known as butyrlcholinesterase or plasma cholinesterase) which act to break down acetylcholine.

Acetylcholine is a critical chemical in the transmission of nerve impulses. Acetylcholinesterase is found in nerve tissue and red blood cells, and pseudocholinesterase is found primarily in the liver.

How the Test is Performed

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

The sample is then taken to the laboratory for evaluation.

How to Prepare for the Test

Adults:
No special preparation is necessary for this test.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

infant test or procedure preparation (birth to 1 year)

toddler test or procedure preparation (1 to 3 years)

preschooler test or procedure preparation (3 to 6 years)

schoolage test or procedure preparation (6 to 12 years)

adolescent test or procedure preparation (12 to 18 years)

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the Test is Performed

Testing for these enzymes is performed to identify exposure to a group of chemicals known as organophosphates (used as pesticides). These chemicals inactivate cholinesterases, and the level of these enzymes serves as an indicator of exposure and risk of toxicity.

A pseudocholinesterase level is also used, although infrequently, to identify liver disease.

This test may also be performed prior to anesthesia with succinylcholine, a paralyzing agent that is eliminated by these enzymes, to exclude a genetic deficiency of these enzymes. This is often done in individuals who have a family history of a prolonged drug effect during anesthesia. Succinylcholine is one agent used before electroconvulsive therapy (ECT) to prevent a full blown seizure during treatment. Your health care provider can determine your potential response to succinylcholine with this test.

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