Test ID: CHED
Pseudocholinesterase, Dibucaine Inhibition, Serum
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Identifying patients who are homozygous for the atypical gene, and have low levels of pseudocholinesterase (PCHE) which are not inhibited by dibucaine
Identifying patients who are heterozygous for the atypical gene, have lower than normal levels of PCHE and varying levels of inhibition with dibucaine
Method Name A short description of the method used to perform the test
Photometric, Acetylthiocholine Substrate with Dibucaine Addition
Includes pseudocholinesterase, total.
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Dibucaine Inhibition
Serum Cholinesterase
Serum Pseudocholinesterase
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Specimen Volume: 0.5 mL
Collection Instructions: For cases of prolonged apnea following surgery, wait 24 hours before obtaining specimen.
Additional Information: Patient's age and sex are required.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild reject; Gross reject |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 7 days |
| Frozen | 7 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Serum cholinesterase, often called pseudocholinesterase (PCHE), is distinguished from acetylcholinesterase or "true cholinesterase," by both location and substrate.
Acetylcholinesterase is found in erythrocytes, in the lungs and spleen, in nerve endings, and in the gray matter of the brain. It is responsible for the hydrolysis of acetylcholine released at the nerve endings to mediate transmission of the neural impulse across the synapse.
PCHE, the serum enzyme, is also found in liver, pancreas, heart, and white matter. Its biological role is unknown.
The organophosphorus-containing insecticides are potent inhibitors of the true cholinesterase and cause depression of PCHE. Low values of PCHE are also found in patients with liver disease. In general, patients with acute hepatitis and chronic hepatitis of long duration will show a 30% to 50% decrease in PCHE values, while patients with advanced cirrhosis and carcinoma with metastases will show a 50% to 70% decrease. Essentially normal values are seen in chronic hepatitis, mild cirrhosis, and obstructive jaundice.
PCHE metabolizes the muscle relaxants succinylcholine and mivacurium, and therefore, alterations in PCHE will influence the physiologic effect of these drugs.
In normal individuals (approximately 94% of the population) certain drugs and other agents, such as dibucaine and fluoride, will almost completely inhibit the PCHE activity.
A small number of patients (<1% of the population) are homozygous for an atypical gene controlling PCHE. These individuals generally have low levels of PCHE which are not inhibited by dibucaine and fluoride, will not hydrolyze the drugs succinylcholine and mivacurium rapidly enough, and may enter a period of prolonged apnea. In addition to fluoride and dibucaine alleles, a "silent gene" has also been identified which shows little or no activity. More recently, the J and K variants also have been identified. All combinations of heterozygotes of the various alleles have been found. This is important because these atypical enzymes will show varying levels of enzyme activity and resistance to dibucaine although the patients clinically show prolonged apnea.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
DIBUCAINE INHIBITION
70-90%
Congenital deficiency: 18-20%
PSEUDOCHOLINESTERASE, TOTAL
Males: 3,100-6,500 U/L
Females
18-49 years: 1,800-6,600 U/L
> or =50 years: 2,550-6,800 U/L
Reference values have not been established for patients that are <18 years of age.
Interpretation Provides information to assist in interpretation of the test results
Patients with normal pseudocholinesterase (PCHE) activity show 70% to 90% inhibition by dibucaine, while patients homozygous for the abnormal allele show little or no inhibition (0%-20%) and usually low levels of enzyme. Heterozygous patients have intermediate PCHE levels and response to inhibitors.
The atypical gene is inherited in an autosomal recessive pattern. In a positive patient, family members should be tested.
Several reports have shown that 65% to 75% of patients who respond abnormally to succinylcholine had at least 1 abnormal gene, had low activity due to an acquired deficiency such as liver disease, or had received an inappropriate dose of drug. The remaining 25% to 35% of patients appeared to have the usual or normal genotype but nevertheless displayed long periods of apnea. Although reasons could not be established, it is possible that these cases represent unknown genotypes. Therefore, although many symptomatic patients will show moderate to significant resistance to dibucaine and low enzyme activity, not all will. In all cases, it is recommended that succinylcholine and mivacurium be avoided, or the dose greatly reduced.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
There are some homozygous and heterozygous individuals who are sensitive to succinylcholine although their total pseudocholinesterase (PCHE) values are normal. A dibucaine inhibition test is necessary in order to confirm the presence of the abnormal allele in these individuals.
Dibucaine inhibition is of no value over total PCHE in attempting to diagnose organophosphorus pesticide exposure. The same is true in liver disease.
Certain drugs and anesthetic agents may inhibit PCHE activity. Therefore, it is recommended that blood specimens be drawn 24 to 48 hours post-operatively on those patients who have experienced prolonged apnea after surgery.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Lockridge O: Genetic variants of human serum cholinesterase influence metabolism of the muscle relaxant succinylcholine. Pharm Ther 1990;47:35-60
2. McQueen MJ: Clinical and analytical considerations in the utilization of cholinesterase measurements. Clin Chim Acta 1995;237:91-105
3. Moss DW, Henderson R: Enzymes. In Tietz Textbook of Clinical Chemistry. 2nd edition. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 1994, pp 877-883
4. Nelson TC, Burritt MF: Pesticide poisoning, succinylcholine-induced apnea and pseudocholinesterase. Mayo Clin Proc 1986;61:750-752
Method Description Describes how the test is performed and provides a method-specific reference
The substrate, acetylthiocholine, is cleaved by pseudocholinesterase (PCHE) into acetate and thiocholine. The thiocholine reacts with dithiobisnitrobenzoic acid (Ellman's reagent) to form the yellow-colored 5-mercapto-2-nitrobenzoic acid which is monitored at 405 nm. The rate of color formation is directly proportional to the PCHE activity.(2)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Sunday; Continuously
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
82480-Pseudocholinesterase, total
82638-Pseudocholinesterase, dibucaine inhibition
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| PCHE | Pseudocholinesterase | 2098-2 |
| DIB | Dibucaine Inhibition | 39354-6 |
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