Cytochrome P450 2C9 (CYP2C9) Genotyping

Test Code

CPT Code

Whole blood or buccal swabs

5 mL of whole blood or four buccal swabs

Minimum Volume
3 mL of whole blood or four buccal swabs

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
CYP2C9 metabolizes approximately 10% of all drugs, including warfarin, phenytoin, non-steroidal anti-inflammatory drugs (NSAIDs), and antihyperglycemic sulphonylureas.  Detecting variants of the CYP2C9 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 CYP2C9 substrates.

Alleles Detected
Active alleles: CYP2C9*1
Inactive alleles: CYP2C9*2, *3, *4, *5, *6, *8, *11, *12

Phenotype Categories

  • Extensive metabolizers (EM) represent the norm for metabolic capacity. Genotypes consistent with the EM phenotype include two active CYP2C9 alleles.
  • Intermediate metabolizers (IM) represent reduced metabolic capacity.  Genotypes consistent with the IM phenotype are those with one active and one inactive CYP2C9 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 CYP2C9 alleles.

Other variants of the CYP2C9 gene that are not detected in this assay may influence drug metabolism.  CYP2C9 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.

Real-time polymerase chain reaction with fluorescence detection.

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