Test Id : 2B6Q
Cytochrome P450 2B6 Genotype, Varies
Useful For
Suggests clinical disorders or settings where the test may be helpful
Aiding in determining therapeutic strategies for drugs that are metabolized by cytochrome P450 (CYP) 2B6
Providing information relevant to bupropion, efavirenz, ketamine, methadone, and nevirapine, as well as other medications metabolized by CYP2B6
Determining the genotype if genotype-phenotype discord is encountered clinically after testing with a less comprehensive genotyping method has occurred
Identifying genotype when required for drug trials and research protocols
Method Name
A short description of the method used to perform the test
Real Time-Polymerase Chain Reaction (RT-PCR) with Allelic Discrimination Analysis
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
2B6
Bupropion metabolism
CYP2B6
Cytochrome P450 2B6 (CYP2B6) Genotyping
Efavirenz metabolism
Ketamine metabolism
Methadone metabolism
Nevirapine metabolism
Ketamine
286
Methadone
Specimen Type
Describes the specimen type validated for testing
Varies
Ordering Guidance
Testing is available as the single gene assay (this test) and as a part of a psychotropic pharmacogenomics panel.
If genotype testing for psychotropic medications is requested, order PSYQP / Psychotropic Pharmacogenomics Gene Panel, Varies.
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Submit only 1 of the following specimens:
Specimen Type: Whole blood
Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: None
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send whole blood specimen in original tube. Do not aliquot.
Specimen Stability Information: Ambient (preferred) 9 days/Refrigerated 30 days
Specimen Type: Saliva
Patient Preparation: Patient should not eat, drink, smoke, or chew gum 30 minutes prior to collection.
Supplies: Saliva Swab Collection Kit (T786)
Specimen Volume: 1 Swab
Collection Instructions: Collect and send specimen per kit instructions.
Specimen Stability Information: Ambient 30 days
Specimen Type: Extracted DNA
Container/Tube: 2 mL screw top tube
Specimen Volume: 100 mcL (microliters)
Collection Instructions:
1. The preferred volume is 100 mcL at a concentration of 50 ng/mcL.
2. Provide concentration of DNA and volume on tube.
Specimen Stability Information: Frozen (preferred) 1 year/Ambient/Refrigerated
Special Instructions
Library of PDFs including pertinent information and forms related to the test
Forms
1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
Blood: 1 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Varies | ||
Useful For
Suggests clinical disorders or settings where the test may be helpful
Aiding in determining therapeutic strategies for drugs that are metabolized by cytochrome P450 (CYP) 2B6
Providing information relevant to bupropion, efavirenz, ketamine, methadone, and nevirapine, as well as other medications metabolized by CYP2B6
Determining the genotype if genotype-phenotype discord is encountered clinically after testing with a less comprehensive genotyping method has occurred
Identifying genotype when required for drug trials and research protocols
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
The cytochrome P450 (CYP) family of enzymes is a group of oxidative/dealkylating enzymes localized in the microsomes of many tissues including the intestines and liver. CYP2B6 is wholly or partially responsible for the metabolism of several commonly prescribed drugs.
The CYP2B6 gene is highly variable with over 38 named alleles. The gene can have multiple sequence variations. Alleles thought to have an impact upon CYP2B6 enzyme function at the time that this test was developed are included in this test (see Table). Individuals without a detectable gene alteration will be reported as CYP2B6*1/*1, but it is possible that these individuals harbor unknown variants that may impact metabolism. In addition, some individuals have genes that are hybrids of CYP2B6 and the CYP2B7 pseudogene. The frequency of these hybrids is unknown, and this assay does not test for these hybrids.
Phenotyping is derived from the Pharmacogene Variation Consortium website(1), an exhaustive review of the CYP2B6 literature, the Clinical Pharmacogenetics Implementation Consortium website(2), and published guidelines.(3) CYP2B6 genotype results are used to predict metabolizer phenotypes. A CYP2B6 phenotype is predicted based upon the number of functional, partially functional, and nonfunctional alleles present in a sample. In rare instances where alleles with unknown function are present in a homozygous or compound heterozygous state, an unknown phenotype occurs. It should be noted that other laboratories may use different phenotype prediction methods as there is no consensus on this at this time. However, the method used here represents the findings of the majority of literature available.
Several medications act as substrates of CYP2B6. CYP2B6-metabolized medications with the highest quality of data for the impact of various CYP2B6 alleles on metabolism are:
-Bupropion
-Efavirenz
-Ketamine
-Methadone
-Nevirapine
Other enzymes may be involved in the metabolism of these drugs. For example, bupropion is also metabolized by CYP2D6. Efavirenz is also metabolized by CYP2A6, although CYP2B6 is the major metabolizing enzyme. Ketamine is also metabolized by CYP2A6, and nevirapine is also metabolized by CYP3A4 and CYP3A5. CYP2A6 testing is not available clinically at the time this document was written, but CYP2D6 (2D6Q / Cytochrome P450 2D6 Comprehensive Cascade, Varies), CYP3A4 (3A4Q / Cytochrome P450 3A4 Genotype, Varies), and CYP3A5 (3A5Q / Cytochrome P450 3A5 Genotype, Varies) testing is available.
There is a variable degree of substrate specificity exhibited by CYP2B6 alleles on these medications. This means that the same allele (ie, *6) may not metabolize all substrates at exactly the same rate.
Drugs that are metabolized by CYP2B6 may require dosage adjustment based on the individual patient's genotype. For example, patients who are poor metabolizers may require much lower than usual doses to achieve optimal response in the case of drugs that are inactivated by the CYP2B6 enzyme. Alternatively, patients who are ultrarapid metabolizers may benefit from increased doses in the case of drugs that are inactivated by CYP2B6 enzyme. In the absence of clear guidance from the US Food and Drug Administration on dosing for various metabolizer phenotypes, patients with either ultrarapid or poor metabolism may benefit by switching to comparable alternate medications that are not primarily metabolized by CYP2B6 or by therapeutic drug monitoring where applicable.
Table. Enzyme Activity of Individual Star Alleles
| Enzyme activity | Examples of CYP2B6 star alleles |
| Normal (extensive) activity | *1, *5 |
| Increased activity | *4, *22 |
| Decreased activity | *6, *7, *9, *11, *14, *15, *19, *20, *26, *27, *36 |
| No or null activity | *8, *12, *13, *16 (also known as *18.002), *18, *35, *38 |
| Unknown activity | *27 |
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.
An interpretive report will be provided.
Interpretation
Provides information to assist in interpretation of the test results
An interpretive report will be provided.
The genotype, with associated star alleles, is assigned using standard allelic nomenclature as published by the Pharmacogene Variation (PharmVar) Consortium.(1)
For additional information regarding pharmacogenomic genes and their associated drugs, see Pharmacogenomic Associations Tables. This resource also includes information regarding enzyme inhibitors and inducers, as well as potential alternate drug choices.
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Rare variants may be present that could lead to false-negative or false-positive results.
Samples may contain donor DNA if obtained from patients who received heterologous blood transfusions or allogeneic hematopoietic stem cell transplantation. Results from samples obtained under these circumstances may not accurately reflect the recipient's genotype. For individuals who have received blood transfusions, the genotype usually reverts to that of the recipient within 6 weeks. For individuals who have received allogeneic hematopoietic stem cell, a pretransplant DNA specimen is recommended for testing.
Genetic test results in patients who have undergone liver transplantation may not accurately reflect the patient's genetic status for the genes on this panel.
This test is not designed to provide specific dosing recommendations and is to be used as an aid to clinical decision making only. Drug-label guidance should be used when dosing patients with medications regardless of the predicted phenotype.(4)
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1. PharmVar. Pharmacogene Variation Consortium. Updated March 3, 2021. Accessed March 22, 2021. Available at www.pharmvar.org/
2. Clinical Pharmacogenetics Implementation Consortium (CPIC). Accessed October 14, 2020. Available at https://cpicpgx.org/
3. Desta Z, Gammal RS, Gong L, et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2B6 and Efavirenz-Containing Antiretroviral Therapy. Clin Pharmacol Ther. 2019;106(4):726-733. doi:10.1002/cpt.1477
4. U.S National Library of Medicine: DailyMed. National Institutes of Health. Accessed October 14, 2020. Available at https://dailymed.nlm.nih.gov/dailymed/index.cfm
Method Description
Describes how the test is performed and provides a method-specific reference
Genomic DNA is extracted from whole blood or saliva. Genotyping for each allele is performed using a polymerase chain reaction (PCR)-based 5'-nuclease assay. Fluorescently labeled detection probes anneal to the target DNA. PCR is used to amplify the section of DNA that contains the variant. If the detection probe is an exact match to the target DNA, the 5'-nuclease polymerase degrades the probe, the reporter dye is released from the effects of the quencher dye, and a fluorescent signal is detected. Genotypes are assigned based on the allele-specific fluorescent signals that are detected.(Unpublished Mayo method)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.
Monday through Friday
Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.
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
Indicates the location of the laboratory that performs the test
Fees :
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.
- Authorized users can sign in to Test Prices for detailed fee information.
- Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
- Prospective clients should contact their account representative. For assistance, contact Customer Service.
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 instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.
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 Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
CPT codes are provided by the performing laboratory.
CPT codes are provided by the performing laboratory.
81479
LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| 2B6Q | CYP2B6 Genotype, V | 72511-9 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| 610082 | CYP2B6 Genotype | 72882-4 |
| 610083 | CYP2B6 Phenotype | 79720-9 |
| 610566 | CYP2B6 Activity Score | 104666-3 |
| 610084 | Interpretation | 69047-9 |
| 610085 | Additional Information | 48767-8 |
| 610086 | Method | 85069-3 |
| 610087 | Disclaimer | 62364-5 |
| 610088 | Reviewed by | 18771-6 |