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HelpTest Code WARSQ Warfarin Response Genotype, Varies
Ordering Guidance
If patient is using medications other than warfarin, the preferred test is 2C9QT / Cytochrome P450 2C9 Genotype, Varies, which tests for only the CYP2C9 gene.
Testing is available as the single gene assay (this test) or as a part of a focused pharmacogenomics panel, which includes testing for the following genes: CYPs 1A2, 2C9, 2C19, 2D6, 3A4, 3A5, 4F2, SLCO1B1, and VKORC1. Order PGXQP / Focused Pharmacogenomics Panel, Varies if multiple pharmacogenomic genotype testing is desired.
Specimen Required
Multiple genotype tests can be performed on a single specimen after a single extraction. See Multiple Genotype Test List in Special Instructions for a list of tests that can be ordered together.
Submit only 1 of the following specimens:
Specimen Type: Whole blood
Container/Tube: Lavender top (EDTA)
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send specimen in original tube.
Specimen Stability Information: Ambient (preferred) 9 days/Refrigerated 30 days
Specimen Type: Saliva
Patient Preparation: Patient should not eat, drink, smoke, or chew gum 30 minutes prior to collection.
Supplies: Saliva Swab Collection Kit (T786)
Specimen Volume: 1 swab
Collection Instructions: Collect and send specimen per kit instructions.
Specimen Stability Information: Ambient 30 days
Specimen Type: Extracted DNA
Container/Tube: 2 mL screw top tube
Specimen Volume: 100 mcL (microliters)
Collection Instructions:
1. The preferred volume is 100 mcL at a concentration of 50 ng/mcL.
2. Include concentration and volume on tube.
Specimen Stability Information: Frozen (preferred)/Ambient/Refrigerated
Forms
1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:
-Neurology Specialty Testing Client Test Request (T732)
-Therapeutics Test Request (T831)
-Cardiovascular Test Request (T724)
Useful For
Identifying patients who may require warfarin dosing adjustments(3,4) including:
-Patients being started on a first prescription for warfarin
-Patients who have previously been prescribed warfarin and have required multiple dosing adjustments to maintain the international normalized ratio in the target range
-Patients with a history of thrombosis or bleeding when taking warfarin
Special Instructions
Method Name
Real-Time Polymerase Chain Reaction (PCR) with Allelic Discrimination Analysis
Reporting Name
Warfarin Response Genotype, VSpecimen Type
VariesSpecimen Minimum Volume
Blood: 0.4 mL
Saliva: 1 swab
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Varies | ||
Reference Values
An interpretive report will be provided.
Interpretation
An interpretive report will be provided that includes assay information, genotype, and an interpretation indicating the patient's predicted warfarin response.
The CYP2C9 and CYP4F2 genotypes, with associated star alleles, are assigned using standard allelic nomenclature as published by the Pharmacogene Variation (PharmVar) Consortium.(5)
Individuals without a detectable alteration in CYP2C9 or CYP4F2 will be designated as CYP2C9*1/*1 or CYP4F2*1/*1
For additional information regarding pharmacogenomic genes and their associated drugs, see Pharmacogenomic Associations Tables in Special Instructions. This resource also includes information regarding enzyme inhibitors and inducers, as well as potential alternate drug choices.
Individuals who have variants in 1 or more gene tested by this assay may require more frequent monitoring of international normalized ratio (INR) to maintain the INR in the target range.
Drug-drug interactions and drug/metabolite inhibition must be considered when prescribing warfarin. Warfarin metabolism may be inhibited through drug-drug interactions, including amiodarone and some statins. It is important to interpret the results of testing and dose adjustments in the context of hepatic and renal function and patient age.
Clinical Reference
1. Oldenburg J, Bevans CG, Muller CR, Watzka M: Vitamin K epoxide reductase complex subunit 1 (VKORC1): the key protein of the vitamin K cycle. Antioxid Redox Signal. 2006;8(3-4):347-353. doi: 10.1089/ars.2006.8.347
2. Watzka M, Geisen C, Bevans CG, et al: Thirteen novel VKORC1 mutations associated with oral anticoagulant resistance: insights into improved patient diagnosis and treatment. J Thromb Haemost. 2011;9(1):109-118. doi: 10.1111/j.1538-7836.2010.04095.x
3. Yuan HY, Chen JJ, Lee MT, et al: A novel functional VKORC1 promoter polymorphism is associated with inter-individual and inter-ethnic differences in warfarin sensitivity. Hum Mol Genet. 2005;14(13):1745-1751. doi: 10.1093/hmg/ddi180
4. Sconce EA, Khan TI, Wynne HA, et al: The impact of CYP2C9 and VKORC1 genetic polymorphism and patient characteristics upon warfarin dose requirements: proposal for a new dosing regimen. Blood. 2005;106(7):2329-2333. doi: 10.1182/blood-2005-03-1108
5. PharmVar: Pharmacogene Variation Consortium. Updated March 3, 2021. Accessed March 22, 2021. Available at www.pharmvar.org/gene/CYP2C9
6. Johnson JA, Caudle KE, Gong L, et al: Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for pharmacogenetics-guided warfarin dosing: 2017 update. Clin Pharmacol Ther. 2017;102(3):397-404. doi: 10.1002/cpt.668
7. Perera MA, Cavallari LH, Limdi NA, et al. Genetic variants associated with warfarin dose in African-American individuals: a genome-wide association study. Lancet. 2013;382(9894):790-796. doi: 10.1016/S0140-6736(13)60681-9
8. McDonald MG, Rieder MJ, Nakano M, Hsia CK, Rettie AE: CYP4F2 is a vitamin K1 oxidase: An explanation for altered warfarin dose in carriers of the V433M variant. Mol Pharmacol. 2009;75(6):1337-1346. doi: 10.1124/mol.109.054833
9. Warfarindosing.org. Washington University; Accessed October 14, 2020. Available at www.warfarindosing.org/Source/Home.aspx
10. U.S National Library of Medicine: DailyMed. National Institutes of Health; Accessed October 14, 2020. Available at https://dailymed.nlm.nih.gov/dailymed/index.cfm
Day(s) Performed
Monday through Friday
Report Available
3 to 10 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
0030U
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| WARSQ | Warfarin Response Genotype, V | 93196-4 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 610175 | Warfarin CYP2C9 Genotype | 46724-1 |
| 610176 | Warfarin VKORC1 Promoter Genotype | 50722-8 |
| 610560 | Warfarin CYP2C9 and VKORC1 Promoter Phenotype | 54451-0 |
| 610177 | Warfarin Resistance Variants | 50722-8 |
| 614410 | Warfarin VKORC1 Resistance Genotype | 50722-8 |
| 610178 | Warfarin CYP4F2 *3 Genotype | 93197-2 |
| 610179 | Warfarin rs12777823 Genotype | 93198-0 |
| 610180 | Interpretation | 69047-9 |
| 610181 | Additional Information | 48767-8 |
| 610182 | Method | 85069-3 |
| 610183 | Disclaimer | 62364-5 |
| 610184 | Reviewed by | 18771-6 |