Cytochrome P450 3A4/3A5 Genotyping

CPT: 81230; 81231
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  • CYP3A4
  • CYP3A5

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 3A4 and 3A5 (CYP3A4/3A5) are drug-metabolizing enzymes involved in the metabolism of several clinically important drugs, including the immunosuppressant tacrolimus. The CYP3A4 and CYP3A5 enzymes have a high degree of sequence similarity and metabolize largely the same set of drugs; genotype and metabolic activity for CYP3A4 and CYP3A5 may therefore be considered together when assessing possible effects on drug response. Individuals with some CYP3A4/3A5 alleles may experience a reduced therapeutic response to drugs that are metabolized by CYP3A4/3A5. CYP3A4/3A5 genotype information can be utilized to predict CYP3A4/3A5 metabolic phenotype, which can be used as an aid in determining a therapeutic strategy for drugs that are metabolized by CYP3A4/3A5. For example, the CYP3A5*3 allele confers poor metabolic activity and has a high frequency in most populations, therefore CYP3A5*3/*3 homozygotes (poor metabolizers) predominate. Treatment with tacrolimus for a poor metabolizer typically requires standard dosing, while intermediate or rapid metabolizers typically require higher starting doses.

Variation in the CYP3A4/3A5 genes can result in normal (NM), intermediate (IM) and poor (PM) drug-metabolizing phenotypes. In general, relative to the *1 allele (normal function), the CYP3A4*22 allele has decreased function whilst CYP3A5 *3, *6 and *7 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 CYP3A/3A5 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 insertions within the CYP3A4/3A5 genes and to assign variant CYP3A4 *22 and CYP3A5 *3, *6, and *7 alleles. *1 denotes detection of the reference (wild-type) sequence at the assessed alleles. No other variants in this gene are detected by this assay.


Birdwell KA, Decker B, Barbarino JM, et al. Clinical pharmacogenetics implementation consortium (CPIC) guidelines for CYP3A5 genotype and tacrolimus dosing. Clin Pharmacol Ther. 2015 Jul;98(1):19-24.25801146
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
512260 Cytochrome P450 3A4/3A5 512211 3A4 Genotype: 81139-8
512260 Cytochrome P450 3A4/3A5 512213 3A4 Metabolic Activity: 81145-5
512260 Cytochrome P450 3A4/3A5 512214 3A5 Genotype: 81140-6
512260 Cytochrome P450 3A4/3A5 512247 3A5 Metabolic Activity: 79717-5
512260 Cytochrome P450 3A4/3A5 512248 Director Review: 72486-4
512260 Cytochrome P450 3A4/3A5 505707 CYP3A4/3A5 Interpretation: 56850-1
512260 Cytochrome P450 3A4/3A5 505708 CYP3A4/3A5 Information: 62364-5
512260 Cytochrome P450 3A4/3A5 000000 MGRM Informed Consent Review N/A

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