Cytochrome P450 2C9 Genotyping

CPT: 81227
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  • DME Genotyping

Expected Turnaround Time

7 - 10 days

Related Documents

Specimen Requirements


Whole blood or Labcorp buccal swab kit (buccal swab collection kit contains 4 swabs and instructions for use of a buccal swab)


2 mL whole blood or one buccal swab kit (4 swabs)

Minimum Volume

1 mL whole blood or two buccal swabs


Lavender-top (EDTA) tube or yellow-top (ACD) tube or Labcorp buccal swab kit


Collect specimen in a lavender-top (EDTA) or yellow-top (ACD) tube, or use a buccal swab kit (4 swabs). Ship whole blood specimen at room temperature or frozen. Ship buccal swab kit at room temperature.

Storage Instructions

Maintain whole blood specimen at room temperature or refrigerated for 28 days or frozen for 2 years. Maintain buccal swabs at room temperature for 2 months.

Stability Requirements



Room temperature

Whole Blood: 28 days

Swabs: 2 Months


Whole Blood: 28 days

Swabs: Unstable


Whole Blood: 2 years

Swabs: Unstable

Causes for Rejection

Hemolysis; quantity not sufficient for analysis; improper container; single buccal swab; wet buccal swab; buccal swabs without outer collection envelope; severely damaged buccal swab envelope; buccal swab envelope received open; frozen glass tube

Test Details


Cytochrome P450 2C9 (CYP2C9) is a drug-metabolizing enzyme involved in the metabolism of several clinically important drugs, including warfarin, phenytoin, siponimod and some nonsteroidal anti-inflammatories. Individuals with some variant CYP2C9 alleles may experience a reduced therapeutic response and may be at risk for side effects from drugs that are metabolized by CYP2C9. CYP2C9 genotype information can be utilized to predict CYP2C9 metabolic phenotype, which can be used as an aid in determining a therapeutic strategy for drugs that are metabolized by CYP2C9. For example, CYP2C9 poor metabolizers mat experience increased concentrations of a drug with a reduced or absent therapeutic response. Warfarin metabolism is reduced by 30-50% by *2 and 90% by *3 alleles: individuals with at least one copy of *2 or *3 have an increased risk of bleeding compared to individuals without *2 or *3. In these instances, a lower warfarin maintenance dose may be required or alternative drugs may be considered.

Variation in the CYP2C9 gene can result in normal (NM), intermediate (IM) and poor (PM) drug-metabolizing phenotypes. In general, relative to the *1 allele (normal function), *2, *5, *8 and *11 alleles have decreased function, while *3, *6 and *13 alleles have no function.


The exact effect of a particular genotype on individual drugs can vary. In addition to genotype, the metabolism of drugs may be influenced by additional factors that include environmental, dietary and other medications; these factors and others should be considered prior to initialing a new therapy. All results must be interpreted in the context of other test results and clinical findings. Results do not rule out the possibility of other variant alleles in CYP2C9 or other variant alleles in other drug metabolism pathways. Patients should speak with their healthcare provider about the individual results of this test.

Molecular-based testing is highly accurate, but as in any laboratory test, rare diagnostic errors may occur.

This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.


DNA analysis is performed by allele-specific real-time polymerase chain reactions (RT-PCR) to detect single-nucleotide polymorphisms (SNPs) and deletion within the CYP2C9 gene and to assign variant CYP2C9 *2, *3, *5, *6, *8, *11 and *13 alleles. *1 denoted detection of the reference (wild-type) sequence at the assessed alleles. No other variants in tis gene are detected by this assay.


Clinical Pharmacogenetics Implementation Consortium (CPIC). Genes-Drugs. CPIC website: Accessed April 2023.
Johnson JA, Caudle KE, Gong L, et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for Pharmacogenetics-Guided Warfarin Dosing: 2017 Update. Clin Pharmacol Ther. 2017 Sep;102(3):397-404.28198005
Karnes JH, Rettie AE, Somogyi AA, et al. Clinical pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2C9 and HLA-B Genotypes and Phenytoin Dosing: 2020 Update. Clin Pharmacol Ther. 2021 Feb;109(2):302-309.32779747
Theken KN, Lee CR, Gong L, et al. Clinical Pharmacogenetics Implementation Consortium Guideline (CPIC) for CYP2C9 and Nonsteroidal Anti-Inflammatory Drugs. Clin Pharmacol Ther. 2020 Aug;108(2):191-200.32189324
US Food and Drug Adminstration (FDA). Table of Pharmacogenetic Associations. FDA website: Accessed April 2023.


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
512143 Cytochrome P450 2C9 Genotyping 512144 2C9 Genotype: 46724-1
512143 Cytochrome P450 2C9 Genotyping 512151 2C9 Metabolic Activity: 79716-7
512143 Cytochrome P450 2C9 Genotyping 512201 Director Review: 72486-4
512143 Cytochrome P450 2C9 Genotyping 512158 Interpretation: 56850-1
512143 Cytochrome P450 2C9 Genotyping 512159 CYP2C9 Information: 62364-5
512143 Cytochrome P450 2C9 Genotyping 000000 MGRM Informed Consent Review N/A

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