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Test ID 2C9B Cytochrome P450 2C9 Genotype by Sequence Analysis, Blood

Useful For

Identifying individuals who may be at risk for altered metabolism of drugs that are modified by CYP2C9

Method Name

Polymerase Chain Reaction (PCR) Followed by DNA Sequence Analysis

Reporting Name

CYP2C9 Genotype, B

Specimen Type

Whole Blood EDTA

Multiple whole blood EDTA genotype tests can be performed on a single specimen after a single extraction. See Multiple Whole Blood EDTA Genotype Tests in Special Instructions for a list of tests that can be ordered together.

 

Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions: Send specimen in original tube.

Forms:

1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. If not ordering electronically, complete, print, and send a Neurology Test Request Form-General (T732) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/neurology-request-form.pdf)

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Ambient (preferred)
  Refrigerated 

Clinical Information

Primary metabolism of many drugs is performed by cytochrome P450 (CYP450), a group of oxidative/dealkylating enzymes localized in the microsomes of many tissues including the intestines and liver. One of these CYP450 enzymes, CYP2C9, participates in the metabolism of a wide variety of drugs including warfarin and phenytoin.

 

CYP2C9-mediated drug metabolism is variable among individuals. Some individuals have CYP2C9 genetic variants that lead to severely diminished or absent CYP2C9 catalytic activity (ie, poor metabolizers). These individuals may metabolize various drugs at a slower rate than normal and may require dosing adjustments to prevent adverse drug reactions.

 

A number of specific CYP2C9 variants have been identified that result in enzymatic deficiencies. The following information outlines the relationship between the variants detected in the assay and their effect on enzyme activity:

 

CYP2C9 Allele

cDNA Nucleotide Change

Effect on Enzyme Metabolism

*1

None (wild type)

Extensive metabolizer (normal)

*2

430C->T

Reduced activity

*3

1075A->C

No activity

*4

1076T->C

Reduced activity

*5

1080C->G

Reduced activity

*6

818delA

No activity

*8

449G->A

Substrate specific

*9

752A->G

Reduced activity

*11

1003C->T

Reduced activity

 

CYP2C9 drug metabolism is dependent on the specific genotype detected, and also on the number and type of drugs administered to the patient. Individuals without a detectable CYP2C19 variant will have the predicted phenotype of an extensive drug metabolizer and are designated as CYP2C19 *1/*1. If an individual is homozygous or compound heterozygous for an allele with no activity, the individual is predicted to be a poor metabolizer. If an individual is heterozygous for an allele with no activity, the individual is predicted to be an intermediate metabolizer. In some cases, a range of potential phenotypes may be given, depending on the combination of alleles identified.

 

Patients who are poor metabolizers may benefit from dose alteration or selection of a comparable drug that is not primarily metabolized by CYP2C9. It is important to interpret the results of testing in the context of other coadministered drugs.

Reference Values

An interpretive report will be provided.

Cautions

Rare genetic variants, if present, could lead to false-negative or false-positive results. If results obtained do not match the clinical findings (phenotype), additional testing should be considered.

 

If the patient has had an allogeneic blood or marrow transplant or a recent (ie, <6 weeks from time of sample collection) heterologous blood transfusion, these results may be inaccurate due to the presence of donor DNA.

                 

CYP2C9 genetic test results in patients who have undergone liver transplantation may not accurately reflect the patient's CYP2C9 status.

 

This method may not detect all variants that result in altered CYP2C9 activity. Therefore, absence of a detectable gene variant does not rule out the possibility that a patient has an altered CYP2C9 metabolism due to other CYP2C9 variants that cannot be detected with this method. Furthermore, when 2 or more gene variants are identified, the cis-/trans- status (whether the variants are on the same or opposite chromosomes) is not always known.  

 

This test detects only the specified genetic variants. Additional findings, such as small insertions and deletions or novel variants, will be reported if determined to be of potential clinical relevance.

Day(s) Performed

Monday, Thursday; 8 a.m.

Report Available

5 days (Not reported Saturday or Sunday)

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81227-CYP2C9 (cytochrome P450, family 2, subfamily C, polypeptide 9) (eg, drug metabolism), gene analysis, common variants (eg, *2, *3, *5, *6)

NY State Approved

Conditional