CYP2C19 Genotype (Cytochrome p450 2C19) for Drug Metabolism

Additional Information:

Epic order code: LAB5169

CPT Code(s):


Specimen Requirements:

Collect at least 3 mL of blood in:

  • EDTA: Lavender-top tube;
  • K2EDTA: Pink-top tube; or
  • ACD Solution A or B: Yellow-top tube.

Severely hemolyzed, clotted and/or frozen blood specimens, and specimens in heparin (green-top) tubes are not accepted.

Specimen Preparation: Transport 3 mL of whole blood. (minimum 1 mL)

Storage/Transport Temperature: Refrigerated

Stability (collection to initiation of testing):

  • Ambient: 72 hours
  • Refrigerated: 1 week
  • Frozen: Unacceptable


This test identifies the CYP2C19 genotype to determine the patient's rate of metabolism for drugs activated or inactivated by this pathway. It has particular importance in metabolizing the drug clopidogrel (Plavix®).



Real-time polymerase chain reaction-based/fluorescence-monitoring test


7-10 days

Reference Values:

No allelic variants detected (*1/*1)


Monday - Friday

Interpretation Data:

Analytical Interpretation: The report includes the patient's diplotype of CYP2C19 genes and is reported using star alleles as follows:

  • *1/*1 for no allelic variant present; or
  • *17/*17 for a homozygous c.991A>G genotype (which has increased function).
CYP2C19 Allelic Variants Tested
Allele Nucleotide Effect Predicted Enzyme Activity
*1 No allelic variant Normal Normal
*2 c.681G>A Splicing defect Non-functional
*3 c.636G>A New stop codon Non-functional
*4 c.1A>G Loss of initiation Non-functional
*5 c.1297C>T R433W Non-functional
*6 c.395G>A R132Q Non-functional
*8 c.358T>C W120R Non-functional
*10 c.680C>T P227L Decreased function
*17 c.991A>G Increased transcription Increased function
Clinical Interpretation: The clinical significance of the result along with recommendations for therapy will be provided.

  • Normal metabolism
  • Impaired metabolism
  • Very imparied metabolism
  • Enhanced metabolism
  • Unknown effect on metabolism
  • Indeterminate result