CYP 2C19

Cytochrome P450 2C19 (CYP2C19) Genotyping

Test Code
Cytochrome P450 2C19 (CYP2C19) 

CPT Code
81225 

Specimen
Whole blood or buccal swabs 

Volume
5 mL of whole blood or four buccal swabs 

Minimum Volume
3 mL of whole blood or four buccal swabs 

Container
Lavender-stopper (EDTA) tube or paper envelope for dried buccal swabs 

Storage Instructions
Maintain at room temperature or refrigerate 

Cause for Rejection
Hemolyzed specimen; quantity not sufficient

General Purpose and Use
CYP2C19 metabolizes approximately 10-15% of all drugs, including clopidogrel, citalopram, diazepam, and many of the proton pump inhibitors.  Detecting variants of the CYP2C19 gene that cause altered enzymatic activity can identify patients who may be at increased risk of having adverse drug reactions or therapeutic failure to standard dosages of CYP2C19 substrates.

Alleles Detected:
Active alleles: *1
Increased activity allele: *17
Inactive alleles: *2, *3, *4, *5, *6, *7, *8, *9, *10

Phenotype Categories

  • Extensive metabolizers (EM) represent the norm for metabolic capacity. Genotypes consistent with the EM phenotype include two active CYP2C19 alleles.
  • Ultra-rapid metabolizers (UM) represent greater than normal metabolic capacity. Genotypes consistent with the EM phenotype include *1/*17 and *17/*17.
  • Intermediate metabolizers (IM) represent reduced metabolic capacity.  Genotypes consistent with the IM phenotype are those with one active or increased activity allele and one inactive CYP2C19 allele.
  • Poor metabolizers (PM) are at increased risk of drug-induced side effects due to diminished drug elimination or lack of therapeutic effect resulting from failure to generate the active form of the drug. Genotypes consistent with the PM phenotype are those with no active CYP2C19 alleles.

Limitations
Other variants of the CYP2C19 gene that are not detected in this assay may influence drug metabolism.  CYP2C19 metabolic capacity is also influenced by concomitant medications, inhibitors, inducers, diet and various disease states.  All factors should be considered as part of the overall patient management strategy.

Methodology
Hybridization capture array technology with automated detection of multiplex PCR products or real-time polymerase chain reaction with fluorescence detection.

Informed Consent
Informed consent for CYP2C19 genotyping is required for patients residing in New York State. The informed consent must be completed along with the test requisition form for these patients.

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