Acetylcholinesterase

Alternative names
Serum cholinesterase; RBC (or erythrocyte) cholinesterase; Pseudocholinesterase; Plasma cholinesterase; Butyrylcholinesterase

Definition

This is a test for the enzymes acetylcholinesterase (also known as RBC cholinesterase) and pseudocholinesterase (also known as butyrylcholinesterase or plasma cholinesterase) which act to break down acetylcholine, a chemical critical 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

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to 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.

For an 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
No special preparation is necessary for this test.

For infants and children:
The preparation you can provide for this test depends on your child’s age and previous experiences. For specific information regarding how you can prepare your child, see the following topics:

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.

Normal Values

The normal value of acetylcholinesterase and pseudocholinesterase depends on the technique, and should be determined by the laboratory performing the test. Typically, normal pseudocholinesterase values range between 8 and 18 U/ml.

Note: U/ml = units per milliliter

What abnormal results mean
Decreased pseudocholinesterase levels may be seen in:

     
  • congenital deficiency  
  • poisoning with organophosphates  
  • liver damage  
  • acute infection  
  • chronic malnutrition  
  • metastasis  
  • myocardial infarction  
  • obstructive jaundice

Smaller decreases are seen during:

     
  • pregnancy  
  • use of oral contraceptives

What the risks are
Risks associated with having blood drawn are slight:

     
  • excessive bleeding  
  • fainting or feeling light-headed  
  • hematoma (blood accumulating under the skin)  
  • infection (a slight risk any time the skin is broken)  
  • multiple punctures to locate veins

Special considerations
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Johns Hopkins patient information

Last revised: December 7, 2012
by Sharon M. Smith, M.D.

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