Pseudocholinesterase and Dibucaine Number

Synonym/acronym: CHS, PCHE, AcCHS.

Common use

To assess for pseudocholinesterase deficiency to assist in diagnosing a congenital deficiency. Special attention must be given to results for preoperative patients because positive results indicate risk for apnea with use of succinylcholine as an anesthetic agent.

Specimen

Plasma (1 mL) collected in a lavender-top (EDTA) tube. Serum (1 mL) collected in a red-top tube is also acceptable.

Normal findings

(Method: Spectrophotometry, kinetic)

Test	Conventional Units
Pseudocholinesterase
Males	3,334–7,031 IU/L
Females	2,504–6,297 IU/L

Dibucaine Number	Fraction (%) of Activity Inhibited
Normal homozygote	79%–84%
Heterozygote	55%–70%
Abnormal homozygote	16%–28%

Description

There are two types of cholinesterase: acetylcholinesterase (AChE), or “true cholinesterase” which is found in red blood cells, lung, and brain (nerve) tissue (see monograph titled “Red Blood Cell Cholinesterase”); and pseudocholinesterase, which is found mainly in the plasma, liver, and heart. Pseudocholinesterase is a nonspecific enzyme that hydrolyzes acetylcholine and noncholine esters. Carbamate and organophosphate insecticides (e.g., parathion, malathion) inhibit its activity.

Patients with inherited pseudocholinesterase deficiency are at risk during anesthesia if succinylcholine is administered as an anesthetic. Succinylcholine, a short-acting muscle relaxant, is a reversible inhibitor of acetylcholinesterase and is hydrolyzed by cholinesterase. Succinylcholine-sensitive patients may be unable to metabolize the anesthetic quickly, resulting in prolonged or unrecoverable apnea. Abnormal genotypes of pseudocholinesterase are detected using the dibucaine and fluoride inhibition tests because, in normal individuals, these chemicals inhibit pseudocholinesterase activity. The prevalence of succinylcholine sensitivity is 1 in 2,000 to 4,000 homozygote and 1 in 500 heterozygote patients. There are more than 15 identified phenotypes; A, AS, S1, S2, F, AF, and FS are associated with prolonged apnea following the use of succinylcholine. Widespread preoperative screening is not routinely performed.

This procedure is contraindicated for

N/A

Indications

Assist in the evaluation of liver function
Screen for abnormal genotypes of pseudocholinesterase in patients with a family history of succinylcholine sensitivity who are about to undergo anesthesia using succinylcholine

Potential diagnosis

Increased in

Increased levels are observed in a number of conditions without specific cause.
Diabetes
Hyperthyroidism
Nephrotic syndrome
Obesity

Decreased in

The enzyme is produced in the liver, and any condition affecting liver function may result in decreased production of circulating enzyme.

(organic phosphate exposure decreases enzyme activity)

(possibly related to decreased availability of transport proteins; condition associated with decreased enzyme activity)

(iatrogenic cause)

(this chemical is a trigger in susceptible individuals)

(chronic infection is known to decrease enzyme activity)

(pathological condition known to decrease enzyme activity)

Critical findings

A positive result indicates that the patient is at risk for prolonged or unrecoverable apnea related to the inability to metabolize succinylcholine. Note and immediately report to the health-care provider (HCP) any critically increased values and related symptoms.
Notify the anesthesiologist if the test result is positive and surgery is scheduled.

Interfering factors

Drugs and substances that may decrease pseudocholinesterase levels include ambenonium, bambuterol, barbiturates, chlorpromazine, cyclophosphamide, echothiophate, edrophonium, esmolol, estrogens, fluorides, glucocorticoids, hexafluorenium, ibuprofen, iodipamide, iopanoic acid, isoflurophate, metoclopramide, monoamine oxidase inhibitors, neostigmine, pancuronium, parathion, phenelzine, physostigmine, procainamide, pyridostigmine, oral contraceptives, and tetrahydroaminacrine.
Drugs that may increase pseudocholinesterase levels include carbamazepine, phenytoin, and valproic acid.
Plasmapheresis decreases pseudocholinesterase levels.
Pregnancy decreases pseudocholinesterase levels by about 30%.
Improper anticoagulant; fluoride interferes with the measurement and causes a falsely decreased value.

Nursing Implications and Procedure

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this test can assist in evaluating for enzyme deficiency.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex. Particularly important to report is exposure to pesticides causing symptoms including blurred vision, muscle weakness, nausea, vomiting, headaches, pulmonary edema, salivation, sweating, or convulsions.
Obtain a history of the patient’s hepatobiliary and musculoskeletal systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

Potential complications: N/A
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
The patient with decreased values should be observed for signs of fluid volume excess related to compromised regulatory mechanisms, decreased cardiac output related to decreased myocardial contractility or arrhythmias, and pain related to inflammation or ischemia.
Social and Cultural Considerations Recognize anxiety related to test results, and be supportive of impaired activity related to weakness and fear of shortened life expectancy. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to genetic counseling services and screening tests for other family members. Educate the patient regarding the use of a medic-alert bracelet to notify health-care workers of increased risk from exposure to medications that may lower pseudocholinesterase activity.
Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include ALT, AST, and red blood cell cholinesterase.
Refer to the Hepatobiliary and Musculoskeletal systems tables at the end of the book for related tests by body system.