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Test Code WARFB Warfarin Sensitivity Genotype by Sequence Analysis, Blood

Useful For

Identifying patients who may require warfarin dosing adjustments(2,3) including:

-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

-Patients being started on a first prescription for warfarin

Reporting Name

Warfarin Sensitivity Genotype, B

Specimen Type

Whole Blood EDTA

Advisory Information

If patient is using drugs other than warfarin, order 2C9B / Cytochrome P450 2C9 Genotype by Sequence Analysis, Blood, which only includes testing for the CYP2C9 gene.

Specimen Required

Multiple whole blood EDTA genotype tests can be performed on a single specimen after a single extraction. See Multiple Whole Blood EDTA Genotype Tests in Special Instructions for a list of tests that can be ordered together.


Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions: Send specimen in original tube.

Specimen Minimum Volume

0.45 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Ambient (preferred)

Reference Values

An interpretive report will be provided.

Day(s) and Time(s) Performed

Monday, Thursday; 8 a.m.

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81227-CYP2C9 (cytochrome P450, family 2, subfamily C, polypeptide 9) (eg, drug metabolism), gene analysis, common variants (eg, *2, *3, *5, *6)
81355-VKORC1 (vitamin K epoxide reductase complex, subunit 1) (eg, warfarin metabolism), gene analysis, common variants (eg, -1639/3673)

LOINC Code Information

Result ID Test Result Name Result LOINC Value
36452 Warfarin Sensitivity In Process
36453 CYP2C9 Star Alleles In Process
36454 VKORC1 -1639 Result In Process
36455 Warfarin Sensitivity Interpretation 69047-9
36456 Reviewed By No LOINC Needed

Method Name

Polymerase Chain Reaction (PCR) Followed by DNA Sequence Analysis