Assess genetic risk of abnormal drug metabolism for drugs metabolized by CYP2C19. May aid in drug selection and dose planning for drugs metabolized by CYP2C19.
- Patient Preparation
- Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
- Specimen Preparation
- Transport 3 mL whole blood. (Min: 1 mL)
- Storage/Transport Temperature
- Unacceptable Conditions
- Plasma or serum. Heparinized specimens.
- Ambient: 72 hours; Refrigerated: 2 weeks; Frozen: 1 month.
Characteristics: The cytochrome P450 (CYP) isozyme 2C19 is involved in the metabolism of many drugs such as clopidogrel, phenytoin, diazepam, R-warfarin, tamoxifen, some antidepressants, proton pump inhibitors, and antimalarials. Variants of CYP2C19 will influence pharmacokinetics of CYP2C19 substrates, and may predict non-standard dose requirements.
Inheritance: Autosomal co-dominant.
Cause: CYP2C19 gene variants result in increased, decreased, or complete deficiency in enzyme activity.
Variants Tested: (Variants are numbered according to NM_000769 transcript).
Decreased function: *9 (rs17884712, c.431G>A); *10 (rs6413438, c.680C>T).
Non-functional: *2 (rs4244285, c.681G>A), *3 (rs4986893, c.636G>A), *4 (rs28399504, c.1A>G), *6 (rs72552267, c.395G>A), *7 (rs72558186, c.819+2T>A), *8 (rs41291556, c.358T>C).
Increased function: *17 (rs12248560, c.-806C>T).
Negative: No variants detected is predictive of *1 functional alleles and normal enzymatic activity.
CYP2C19*2: African American 18.3 percent, Caucasian 14.6 percent, Middle Eastern 13.2 percent, Oceanian 54.9 percent, South Asian 34.4 percent
CYP2C19*3: African American 0.3 percent, Caucasian 0.6 percent, Middle Eastern 2.6 percent, Oceanian 13.9 percent, East Asian 8.5 percent
CYP2C19*17: African American 19.4 percent, Caucasian 21.5 percent, Oceanian 2.5 percent, South Asian 16.5 percent
Other alleles are rare, with allele frequencies of less than 1 percent in all populations studied.
Clinical Sensitivity: Drug-dependent.
Methodology: Polymerase chain reaction (PCR) and fluorescence monitoring.
Analytical Sensitivity and Specificity: Greater than 99 percent.
Limitations: Only the targeted CYP2C19 variants will be detected by this panel. Diagnostic errors can occur due to rare sequence variations. Risk of therapeutic failure or adverse reactions with CYP2C19 substrates may be affected by genetic and non-genetic factors that are not detected by this test. This result does not replace the need for therapeutic drug or clinical monitoring.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|Component Test Code*||Component Chart Name||LOINC|
- P450 2C19 Genotyping
- Treatment Resistant Antidepressant Panel