Cholinesterase

Test Description

There are two enzymes which hydrolyze acetylcholine (ACh): acetylcholinesterase,
or true cholinesterase, and pseudocholinesterase, or serum cholinesterase.
Acetylcholinesterase, which is present in nerve tissue, the spleen, and the gray matter
of the brain, helps with the transmission of impulses across nerve endings to
muscle fibers. Pseudocholinesterase, produced mainly in the liver, appears in small
amounts in the pancreas, intestine, heart, and white matter of the brain.


Two groups of anticholinesterase chemicals, organophosphates and muscle
relaxants, either affect or are affected by these enzymes. Organophosphates, which
inactivate acetylcholinesterase, are found in many insecticides and nerve gas.
Muscle relaxants, such as succinylcholine, are normally destroyed by pseudocholinesterase.
If, however, there is a lack of pseudocholinesterase, the patient may
experience a prolonged period of apnea if given muscle relaxants during surgery.
Thus, patients who are to receive such drugs during surgery should be pretested for
cholinesterase.
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Normal Values

7–19 U/mL 7–19 kU/L (SI units)

Possible Meanings of Abnormal Values

Decreased
Acute infections
Anemia
Chronic malnutrition
Cirrhosis with jaundice
Dermatomyositis
Hepatitis
Inability to hydrolyze muscle relaxants in surgery
Infectious mononucleosis
Metastasis
Myocardial infarction
Poisoning from organic phosphate insecticides
Tuberculosis
Uremia
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Contributing Factors to Abnormal Values

• Hemolysis of the blood sample will alter test results.
• Due to medications used during surgery, cholinesterase levels should not be checked
in the recovery room.
• Drugs which may decrease cholinesterase levels: atropine, caffeine, chloroquine
hydrochloride, codeine, cyclophosphamide, estrogens, folic acid, MAO-inhibitors,
morphine sulfate, neostigmine, oral contraceptives, phenothiazines, physostigmine,
phospholine iodine, pyridostigmine bromide, quinidine, quinine sulfate, succinylcholine,
theophylline, vitamin K.

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Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• No fasting is required before the test.
• Medications which might affect the cholinesterase level should be held for 24 hours
before the sample is drawn.
• If surgery is planned, the blood should be drawn at least 2 days prior to surgery.
Two groups of anticholinesterase chemicals, organophosphates and muscle
relaxants, either affect or are affected by these enzymes. Organophosphates, which
inactivate acetylcholinesterase, are found in many insecticides and nerve gas.
Muscle relaxants, such as succinylcholine, are normally destroyed by pseudocholinesterase.
If, however, there is a lack of pseudocholinesterase, the patient may
experience a prolonged period of apnea if given muscle relaxants during surgery.
Thus, patients who are to receive such drugs during surgery should be pretested for
cholinesterase.

Procedure

• A 5-mL blood sample is drawn in a lavender-top (EDTA) tube and 2 mL in a red-top collection
tube (no gel).
• Gloves are worn throughout the procedure.

Posttest

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.